System and method for measuring microbial activity

Abstract

A system for measuring microbial activity comprises a support comprising a plurality of locations, each location being configured to accommodate the plug of at least one reactor, an agitator device positioned below the support, a transducer positioned above the support, and a movement device configured to move the transducer.

Description

SYSTEM AND METHOD FOR MEASURING ACTIVITY MICROBIAL FIELD OF THE INVENTION

[0001] The present invention relates to a system for measuring microbial activity and more specifically for measuring biodegradability. STATE OF THE ART

[0002] One of the major industrial challenges is producing safe substances with a good ecological profile. Professionals in the chemical, food, cosmetics, and medical sectors must therefore assess the ecological risks that may arise from their substances, particularly by measuring microbial activity. These measurements are also defined by standards.

[0003] However, known systems and procedures for measuring microbial activity are not satisfactory.

[0004] Indeed, most microbial activity measurements are carried out manually with bulky and expensive devices.

[0005] Some systems offer automation of the measurement procedure. However, these systems require human intervention for certain steps of the process. Furthermore, these processes require the reactors to be opened to allow the sensors to perform measurements. This creates exchanges between the outside air and the air contained in the reactor, which fundamentally alters the kinetics of microbial activity and leads to measurement biases. Finally, known systems do not necessarily meet the testing standards imposed by regulations.

[0006] US Patent 9,803,169 discloses a microbial activity measurement system comprising a multi-well plate in which samples are directly into the wells. However, this system is not satisfactory. Indeed, when at least one of the wells is used or defective, the entire plate must be discarded, which increases costs and, in some cases, involves interrupting the measurement of other samples. In addition, all the wells in a plate have fixed volumes determined at the time of manufacture. Thus, the reactor volumes cannot be chosen independently by the user at the time of measurement.

[0007] US patent application US 2014 / 038276 discloses a cylindrical, hermetic reactor comprising a detachable base for opening and closing the reactor. A sensor is arranged on the detachable base. However, since the base is a small element, it is the most sensitive element of the reactor. Therefore, modifying this detachable base to integrate the sensor involves a risk of degradation of the base and therefore a risk of leakage.

[0008] There is therefore a need for a system and method for measuring microbial activity that are automated in order to increase the speed of tests and that allow reliable and accurate measurement of microbial activity without altering the kinetics. In addition, the method must comply with current regulations. Preferably, there is also a need for a system that can contain one or more samples hermetically in volumes chosen by a user while ensuring continuity of measurement even in the event of degradation of one of the samples.

[0009] The aim of the invention is therefore to provide a system for measuring microbial activity comprising: at least one support, each support comprising a plurality of locations configured to accommodate a reactor, at least one stirring device, at least one transducer configured to interact with a point sensor positioned inside a reactor and a device for moving the at least one transducer. SUMMARY

[0010] For this purpose, the present invention relates to a system for measuring microbial activity comprising: At least one support, each support comprising a plurality of upwardly open locations, each location being configured to accommodate a reactor, each reactor comprising a cap adapted to be arranged in the location, preferably each location is upwardly open so as to position the bottom of the reactor above the reactor cap, each reactor being adapted to hermetically contain a sample, each location comprising a center defining a measurement axis perpendicular to the support; At least one stirring device positioned under the support, each stirring device being capable of stirring the sample in a reactor; At least one transducer positioned above the support, each transducer being configured, when aligned with the measurement axis of one of the locations of the support, to interact with a point sensor positioned inside a reactor placed in said location, the point sensor then being aligned with the measurement axis, the point sensor being configured to measure at least one marker of microbial activity; and A moving device configured to move the at least one transducer to successively align it with the measurement axis of several locations of the support.

[0011] Indeed, this system allows measurement of microbial activity without removing the reactor cap. Thus, the reactor remains airtight throughout the incubation period. Consequently, the kinetics of microbial activity are not altered during the measurement, which reduces measurement bias.

[0012] In addition, the reactor cap does not need to be modified to allow the insertion of measuring tools inside the reactor. The cost of setting up the system is therefore reduced and the reactor remains perfectly sealed and safe because the absence Changing the cap also results in a reduction in the risk of damage to the cap or reactor.

[0013] In addition, the reactor is independent of the support and is unique for each sample (it can therefore only contain one sample). This allows the use of reactors with a simple structure, i.e., those that are not manufactured specifically for use in a particular microbial activity measurement system. The simplicity of the reactor ensures better hermeticity. The uniqueness of the reactor allows one of the reactors to be easily replaced if it is defective without stopping the measurement of samples placed in other reactors. Finally, the use of unique and independent reactors allows for greater flexibility in terms of reactor volume.

[0014] Furthermore, incubation and microbial activity measurements can take place in a single system without the need for handling or logistics to transport reactors from an incubation system to a measurement system.

[0015] Positioning the stirring devices below the support and the transducer above the support allows the transducer to be moved in a two-dimensional plane without being hindered by the presence of the stirring devices.

[0016] Finally, the positioning of the caps in the open-topped holder means that the reactors have their bottoms facing upwards. Thus, the transducer can be moved as close as possible to the point sensor of each reactor while remaining in a plane, without the need for complex three-dimensional movements - for example, raising and lowering the transducer for each reactor to avoid reactor plugs with each movement. Furthermore, in the event of a reactor leak, placing the transducer and displacement device above the holder prevents damage to the transducer and displacement device from sample flow in the direction of gravity.

[0017] This therefore implies a reduction in the cost of the system which is all the greater the more automated the system is. Thus, a system comprising a single transducer only requires a displacement device in one plane (in two dimensions).

[0018] According to one embodiment, each stirring device comprises a mobile magnetic attractor positioned under a location and capable of cooperating with a magnetic stirrer arranged inside the reactor placed in this location, the mobilization of the magnetic attractor making it possible to mobilize the magnetic stirrer in the reactor.

[0019] The positioning of the stirring device under the support and the cap of each reactor downwards allows, in the case of stirring by magnetization, to position the magnetic stirrer completely in the liquid and as close as possible to the magnetic attractor.

[0020] According to one embodiment, the transducer allows interaction by fluorescence.

[0021] According to one embodiment, at least one of the microbial activity markers is selected from the amount of oxygen, the amount of carbon dioxide, the amount of methane, the concentration of a predetermined chemical molecule, and / or the pressure inside the reactor.

[0022] According to one embodiment, the microbial activity measurement system further comprises an enclosure configured to protect the at least one transducer from external disturbances.

[0023] According to one embodiment, the microbial activity measurement system further comprises a fluid recovery tank between the support and the stirring device.

[0024] This protects the stirring device in the event of a leak from one or more reactors.

[0025] The present invention also relates to a reactor capable of hermetically containing a sample, the reactor having a side wall, a bottom and a ring on which a stopper fits, the ring being opposite the bottom, the ring having an alignment axis, a point sensor being arranged inside the reactor, on the bottom of the reactor and placed on the alignment axis, the point sensor being configured to measure at least one microbial activity marker, the reactor being capable of being accommodated in a location of a support of the system described above so that the cap fits into the location and the alignment axis overlaps with the measurement axis of said location.

[0026] Indeed, the reactor that can be used in the system of the invention is advantageously a readily commercially available reactor that does not require any structural adaptation. Only the point sensor needs to be fixed in the bottom of the reactor. This allows for a less expensive and easy-to-use system and operation compared to known systems.

[0027] The reactor according to the invention is advantageous in the context of using the system described above because it allows the sensor to be placed as close as possible to the transducer while avoiding modifying the reactor cap to integrate the sensor. Indeed, the caps are the most sensitive elements of the reactors because they present the greatest risk of leakage. Thus, not modifying the cap ensures the hermeticity of the reactor.

[0028] The point sensor can, for example, be pre-calibrated, which eliminates the need for a sensor calibration step before using the reactor.

[0029] According to one embodiment, the bottom has a thickness of between 2 mm and 6 mm.

[0030] According to one embodiment, the bottom has a curvature of between 600 mm and 3000 mm.

[0031] The present invention also relates to an applicator for placing a point sensor on the bottom of a reactor in order to prepare a reactor as described above, the applicator comprising an adjustable centering element on the reactor ring and a positioning element for placing the point sensor on the bottom of the reactor and on the alignment axis.

[0032] The present invention also relates to a method of using a microbial activity measurement system as described above, the method comprising the steps of: Providing at least one reactor, the reactor having a wall comprising a side wall, a bottom and a ring onto which a plug fits, the ring being opposite the bottom, the ring having an alignment axis; For each reactor: ■ Placing at least one point sensor configured to measure at least one microbial activity marker inside the reactor, on the bottom of the reactor and on the alignment axis; ■ Introduction of a sample into the reactor; ■ Closing the reactor with a cap; ■ Placing the reactor in the support by adjusting the plug in one of the locations of the support, such that the alignment axis overlaps with the measurement axis of said location, the bottom of the reactor being positioned above the ring; Stirring the sample using the stirring device; Aligning at least one of the transducers with at least one of the measuring axes using the displacement device; Interaction of said transducer with the point sensor in order to measure at least one marker of microbial activity.

[0033] According to one embodiment, the reactor is placed in the support, by adjusting the plug in one of the locations of the support.

[0034] According to one embodiment, the bottom of the reactor is positioned above the ring during placement of the reactor in the support.

[0035] According to one embodiment, the alignment and interaction steps are repeated at predetermined time intervals for at least one reactor.

[0036] According to one embodiment, the method further comprises, before placing the sample in the reactor, a step of calibrating the point sensor.

[0037] According to one embodiment, the method of use allows the measurement of the biodegradability of the sample, the sample comprising a microbial inoculum.

[0038] According to one embodiment of the method of use, the point sensor is configured to measure the amount of oxygen within the reactor.

[0039] According to one embodiment of the method of use, the transducer interacts with the point sensor by fluorescence. DEFINITIONS

[0040] In the present invention, the terms below are defined as follows:

[0041] “Sample” means a liquid comprising at least one substance for which a measurement of microbial activity – for example, a measurement of biodegradability or biodegradation – is carried out. This substance may be soluble in the liquid, dispersed in the liquid or volatile.

[0042] “Substance” means any molecule, polymer, or mixture of molecule and polymer. DESCRIPTION OF FIGURES

[0043] Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate exemplary embodiments thereof which are not limiting in nature.

[0044] Figure 1 represents the microbial activity measurement system according to one embodiment.

[0045] Figure 2 shows the system in use. The transducer is successively positioned above each reactor using the displacement device in order to interact with the corresponding point sensor.

[0046] Figure 3 shows the reactor support according to an embodiment comprising six locations.

[0047] Figure 4 shows a set of eight reactor holders according to an embodiment in which each holder includes six locations. Reactors are placed in six of the eight holders.

[0048] Figure 5 shows a reactor and its cap according to one embodiment. A point sensor is placed at the bottom of the reactor.

[0049] Figure 6 shows an applicator according to one embodiment.

[0050] Figure 7 shows the application of the point sensor in the bottom of the reactor using the applicator of Figure 6.

[0051] Figure 8 shows the agitation according to one embodiment.

[0052] Figure 9 shows a set of stirring devices according to one embodiment.

[0053] Figure 10 shows a reactor placed in a location with the cap at the bottom just above a stirring device.

[0054] Figure 11 shows the evolution of the oxygen rate C (in percent) over time T (in days) for each of the six reactors in the example. DETAILED DESCRIPTION

[0055] The present invention relates to a system 100 for measuring microbial activity. The system 100 is capable of measuring any type of microbial activity in a sample. For example, the system 100 makes it possible to determine the biodegradability of certain chemical substances by measuring the oxygen consumption by the microbial inoculum present in the sample. In another example, the system 100 makes it possible to determine the activity of fermentation starter strains (or starter cultures) allowing the acceleration of fermentation processes in agri-food, pharmaceutical, biotechnological and renewable energy processes. In yet another example, the system 100 makes it possible to measure the effect of an active ingredient - for example an antibiotic - or a molecule on the growth of bacteria or fungi in medicine or cosmetics.

[0056] System 100 allows in particular the implementation of the 301 AF methods for measuring ready biodegradability according to the OECD Guidelines for the Testing of Chemicals (adopted in 1992 and amended in 2013). In these methods, the sample is placed in a filled and hermetically sealed bottle. The bottles are incubated at constant temperature and in the dark for 28 days. A marker of microbial activity is measured, for example dissolved organic carbon (301 A and 301 E), CO2 released (301 B), oxygen consumption (301 C and 301 F), or dissolved oxygen (301 D), making it possible to estimate the biodegradation that has taken place in the sample. The measurement can also relate to a quantity derived from or correlated with one of these markers.

[0057] In order to be able to carry out microbial activity measurements, in particular in the case of tests using OECD 301 AF methods, the system 100, shown in Figures 1 and 2, comprises: At least one 120 support; At least one stirring device 140 positioned under the support 120; At least one transducer 160 positioned above the support 120; and A moving device 165 configured to move F at least one transducer 160.

[0058] Each support 120 includes a plurality of upwardly open locations 125 as shown in Figure 3. In the present disclosure, the terms "up" and "down" are defined according to the direction of gravity when the system or element is in a position of use. The "top" is therefore above the "bottom" in the direction of gravity.

[0059] Preferably, each support 120 comprises 2x3 locations 125. Each location 125 comprises a center defining a measurement axis Al perpendicular to the support 120.

[0060] Each location 125 is configured to accommodate a reactor 180 as shown in Figure 4. This Figure 4 represents a system 100 comprising eight supports 125, each support comprising 2x3 locations 125 allowing automatic measurement of up to 48 reactors 180.

[0061] The reactors 180 are independent elements of the support 120. Indeed, the support 120 is not configured to directly accommodate a sample. The sample will be placed in the reactor 180 which will be arranged in the support 120. In other words, a support comprising wells which can be closed and in which a sample is placed is not considered to be a reactor 180 within the scope of the present disclosure.

[0062] The reactors 180 that can be accommodated in the system 100 can be of any type. For example, the reactors 180 can be round laboratory bottles with screw caps of the Duran Schott brand (registered trademark) with a volume of between 50 mL and 1 L. Preferably, the reactors 180 have a volume of between 100 mL and 250 mL. The volume of 133 mL is a good compromise between the space saving required for 48 tests and the volume of air required for microbial activity.

[0063] A reactor 180 by definition has a wall and a ring on which a cap 182 fits. Thus, the reactors have a simple structure, that is to say that the reactors are not manufactured specifically for use in a particular microbial activity measurement system. Thanks to the simple structure of the reactor without gas inlet / outlet or internal stirring device, the hermeticity of the reactor is more easily controlled. The reactor is a single-use consumable: once used, it can be discarded instead of being sterilized. In addition, the samples are placed in independent reactors. Thus, if one of the reactors is defective, it can be replaced without stopping the measurement of samples placed in the other reactors. In addition, the use of single and independent reactors allows for greater flexibility in terms of reactor volumes, which can be different and chosen according to need. All these advantages cannot be achieved by using multi-well plates in which a sample is directly deposited. Indeed, in known systems using a multi-well plate, when at least one of the wells is used or defective, the entire plate must be discarded. In addition, all the wells in a plate have fixed volumes determined at the time of manufacture. Thus, the reactor volumes cannot be chosen independently by the user at the time of measurement.

[0064] The ring is the upper part of the reactor 180 on which the cap 182 is positioned. The ring therefore corresponds to the edge of the wall. In the present disclosure, the terms “upper part of the reactor 180” and “lower part of the reactor 180” are defined according to the direction of gravity when the reactor 180 is in an installation position, that is to say in a position which allows the injection of the sample into the reactor 180 before the use of the reactor 180 in the system 100. In other words, the ring defining an opening allowing access to the interior of the reactor 180, the upper part of the reactor 180 is therefore the part comprising the ring and on which the cap 182 is fitted. The ring may comprise a thread onto which the cap 182 is screwed or a ring onto which the cap 182 is clipped. When the plug 182 is not positioned on the ring, the latter allows access to the interior of the reactor 180.An example of a reactor shape 180 is shown in Figure 5. However, the morphology of the wall of the reactor 180 is of little importance. The wall may be transparent, preferably made of glass, for example borosilicate glass. The glass ensures sufficient sealing against gas diffusion. The wall comprises a side wall 184a and a bottom 184b. The bottom 184b is arranged in the lower part of the reactor 180. In other words, the bottom 184b is opposite the ring onto which a plug 182 fits. The bottom 184b is therefore opposite the plug 182 when the latter is fitted onto the ring. The bottom 184b and the plug 182 are not necessarily parallel to each other. The bottom 184b may have a thickness of between 2 mm and 6 mm, preferably between 3.5 mm and 4.5 mm. The 184b bottom, even though it may be flat, can. also have a radius of curvature between 600 mm and 3000 mm, preferably between 900 mm and 1250 mm. The ring comprises a center defining an alignment axis A2 extending between the ring and the bottom 184b.

[0065] Thus, more precisely, each location 125 is configured to accommodate a plug 182. Preferably, each location 125 is configured so that its shape is adjusted to the shape of the plug 182 that will be accommodated. By "adjusted" it should be understood that the plug can be inserted into the location but that it is placed there in such a way as to avoid any movement and therefore any change in position of the reactor 180. Alternatively, the reactors 180 are chosen so that their plugs fit into the locations 125. Thus, this makes it possible to maintain the reactor 180 vertically "upside down" so that the plug 182 is positioned under the bottom 184b in the direction of gravity. Thus, in use, the upper part of the reactor 180 is positioned downwards and therefore below the lower part of the reactor 180 which is positioned upwards.Preferably, the plug 182 is fitted in the location 125 so that the alignment axis A2 overlaps with the measurement axis A1 of said location 125.

[0066] Each reactor 180 is capable of hermetically containing a sample. The hermetic nature of the reactor 180 is very important because it allows for precise measurement of microbial activity isolated from external parameters. The environment inside the reactor is therefore controlled. The simplicity of the structure of the reactors 180 makes it possible to guarantee their hermeticity even when they are placed "upside down". Indeed, reactors comprising an internal stirring system and / or gas inlets / outlets cannot be used "upside down" unless additional sealing elements are integrated, which reduces the hermeticity of the reactor and therefore increases the risk of leakage.

[0067] The sample preferably contains a microbial inoculum, i.e. a set of microorganisms (for example bacteria, fungi or protists) whose activity will be measured over time. But the system 100 can also use a single species of microorganisms. The activity of the microbial inoculum is measured by a point sensor 150 (spot sensor in English) placed inside the reactor 180, on the bottom 184b of the reactor 180. The placement of the point sensor 150 in the bottom of the reactor positioned "head down" (and therefore the bottom directed towards the transducer 160 arranged above the support) is advantageous in the context of the use of the reactor 180 in the system described here because this makes it possible to place the sensor as close as possible to the transducer 160 while avoiding modifying the reactor cap 182 to integrate the sensor 150. Indeed, the caps are the most sensitive elements of the reactors because they present the greatest risk of leakage. Thus, not modifying the cap 182 makes it possible to guarantee the hermeticity of the reactor 180. The point sensor 150 is preferentially placed on the alignment axis A2. Thus, when the cap 182 is received in the location 125, the point sensor 150 is aligned with the measurement axis A1.

[0068] In order to facilitate the repeatability of the alignment of the point sensor on the alignment axis A2, an applicator 190 may be used. An example of an applicator is shown in FIG. 6. The applicator 190 comprises a centering element 192 adjustable on the ring of the reactor 180. For example, if the ring comprises a thread for screwing the cap 182, the centering element 192 may also comprise a thread in order to screw it onto the ring in the same manner as the cap 182. The applicator 190 further comprises a positioning element 194 for placing the point sensor 150 on the bottom 184b of the reactor 180 and on the alignment axis A2.

[0069] The application of the point sensor 150 using this applicator 190 is shown in Figure 7. The centering element 192 is fitted onto the ring and the positioning element 194 has a length enabling the point sensor 150 to be fixed to the bottom 184b. The fixing of the point sensor 150 can for example be carried out by gluing. After fixing the sensor 150, the applicator 190 is removed from the reactor. The applicator 190 can advantageously be reused for all reactors of the same format.

[0070] The point sensor 150 is preferably configured to measure at least one marker of microbial activity, for example, the rate or quantity of carbon dioxide CO2, the rate or quantity of methane CEE, the pressure, the concentration of a predetermined chemical molecule and / or the temperature in the reactor 180. Preferably, the marker of microbial activity is the rate or quantity of oxygen dissolved (OECD 301 D method). Indeed, during the biodegradation of substances, the microbial inoculum consumes oxygen to oxidize said substances. Thus, the quantity of dissolved oxygen consumed, also called biochemical oxygen demand (BOD), makes it possible to quantify the quantity of materials that can be degraded and therefore the biodegradability of the sample.

[0071] These microbial activity markers can be measured directly in the sample. These microbial activity markers are preferably measured in the atmosphere of the reactor 180, i.e. above the surface of the sample. The point sensor 150 can advantageously be pre-calibrated. This makes it possible to avoid a step of calibrating the point sensor 150 before using each reactor 180.

[0072] As mentioned above, the system 100 comprises a stirring system 140 positioned under the support 120. The stirring system 140 is therefore external to the reactor 180. Each stirring device 140 of the system 100 is capable of stirring (mixing) the sample in a reactor 180. Mixing the sample is advantageous because this allows for homogeneous activity of the microbial inoculum throughout the sample. The stirring device 140 is preferably configured to stir the sample without opening the cap 182 of the reactor 180. The placement of the stirring system 140 under the support 120 is advantageous because, under the effect of gravity, the sample is placed at the bottom of the reactor 180. Thus, the stirring system 140 is as close as possible to the sample.

[0073] The stirring device may, for example, be a vibrating or rotating platform on which the support(s) are placed.

[0074] Preferably, each stirring device 140 comprises a mobile magnetic attractor 144 positioned under a location 125 and capable of cooperating with a magnetic stirrer 148 arranged inside the reactor 180 housed in this location 125. The magnetic stirrer 148 may for example be a magnetic bar. The mobilization of the magnetic attractor 144 therefore makes it possible to mobilize the magnetic stirrer 148 in the reactor 180. For example, the mobilization of the magnetic attractor 144 is an actuation or movement of this attractor 144, for example using an actuator 146 such as a motor. In Figure 8, the motor 146 makes it possible, for example, to rotate in a direction F1 a propeller 142 comprising two magnets forming the magnetic attractor 144. The rotation of the two magnets involves the rotation in the direction F2 of the magnetic stirrer 148 thanks to the magnetic attraction force. The movement of the magnetic stirrer 148 allows the stirring of the sample included in the reactor 180. An example of a set of magnetic attractors 144 is shown in Figure 9. In this figure, the magnetic attractors 144 are positioned in a base which advantageously makes it possible to match the position of the magnetic attractors 144 with the locations 125 of support 120 as shown in Figure 3.

[0075] The positioning of the reactor 180 "upside down" advantageously allows the movement of the magnetic stirrer 148, which is placed by gravitational attraction in the cap 182, without risk of damage to the point sensor 150 fixed on the bottom 184b. In addition, in this configuration, the magnetic stirrer 148 can be completely immersed in the sample, which allows for better mixing efficiency. Finally, the positioning of the magnetic stirrer 148 in the cap of the reactor 180 allows it to be brought closer to the magnetic attractor 144 and to further improve the mixing thanks to the greater magnetic attraction force between these two elements.

[0076] Advantageously, the system 100 may further comprise a fluid recovery tank positioned between the support 120 and the stirring devices 140. This makes it possible to recover the fluid (sample) in the event of a leak from the reactors 180 and to avoid damaging the actuators 146.

[0077] Each transducer 160 of the system 100 is configured, when aligned with the measurement axis A1 of one of the locations 125, to interact with a point sensor 150 of a reactor 180 accommodated in this location 125. The interaction allows the transmission of the measurement carried out by the point sensor 150 to the transducer 160 and / or the sending of an instruction signal from the transducer 160 to the point sensor 150. Thus, the measurement carried out in situ is read through the wall of each reactor 180 without opening the cap 182. The reactor 180 then remains hermetically sealed throughout the incubation and measurement period, which makes it possible not to alter the kinetics of the microbial activity. In the same way, this makes it possible not to modify the cap or the wall of the reactors 180 to insert measuring elements. Thus, the reactors 180, which are consumables, can be reactors 180 commonly found commercially and therefore less expensive. In addition, the absence of modification of the cap or the wall maintains the safety of use of the reactors 180.

[0078] The glass wall of the reactor 180 advantageously allows the passage of the measurement or instruction signal using a wavelength between 0.38 pm and 0.78 pm. For example, the interaction between the transducer 160 and the point sensor 150 is carried out by fluorescence. For example, the transducer 160 used is the Electro-Optical Module EOM-O2-FOM from Presens associated with point sensors 150 PSt3 from Presens.

[0079] In the context of a fluorescence measurement, the point sensor 150 contains a fluorescent marker whose fluorescence yield is linked to the concentration of a molecule in the sample. Thus, after equilibrium has been reached between the sample and the point sensor 150 - this equilibrium being rapid with respect to the characteristic time of evolution of the sample - the fluorescence intensity of the point sensor is an indirect measurement of the concentration of said molecule, for example a marker of microbial activity. It should be noted that the measurement can be very indirect. Thus, the point sensor 150 can be sensitive to the oxygen concentration in the reactor headspace, this concentration of oxygen gas itself being in equilibrium with the dissolved oxygen whose concentration is to be measured.

[0080] An exemplary configuration of the system 100 in which a single location 125 is represented is shown in FIG. 10 with the magnetic attractor 144 positioned below the location closest to the reactor cap 180 and the transducer 160 positioned above the bottom 184b of the reactor 180 closest to the point sensor 150. The measurement axis A1 is then aligned with the alignment axis A2.

[0081] In order to align the transducer 160 with the measurement axis A1, the system 100 comprises a displacement device 165. The positioning of the reactor 180 “upside down” and the fixing of the point sensor 150 on the bottom 184b advantageously makes it possible to successively position the transducer 160 as close as possible to each of the sensors 150 in a simple movement in a plane. The displacement device 165 thus does not necessarily have to be configured to perform an up-and-down movement each time it passes from one reactor 180 to the other. The precision with regard to the positioning of the transducer 160 is preferably of the order of a millimeter. In order to achieve such precision, a technology based on CNC (Computer Numerical Control) can be used.

[0082] Advantageously, the system 100 may further comprise an enclosure configured to protect the at least one transducer from external disturbances.

[0083] The system presented above advantageously allows for reducing measurement bias.

[0084] The invention also relates to a method of using the microbial activity measurement system 100 presented above. The method comprises the steps of: - Supply of at least one 180 reactor; - For each reactor 180: ■ Placement of at least one point sensor 150 inside the reactor 180, on the bottom 184b of the reactor 180 and on the alignment axis A2; ■ Introduction of a sample into the reactor 180, preferably via the opening defined by the ring; ■ Closing of reactor 180 with cap 182; ■ Placing the reactor 180 in one of the locations 125 of the support, such that the alignment axis A2 overlaps with the measurement axis Al of the location 125, the bottom 184b of the reactor 180 being positioned above the ring; Stirring the sample using the stirring device 140; Alignment of at least one of the transducers 160 with at least one of the measuring axes A1 using the displacement device 165; Interaction of transducer 160 with point sensor 150.

[0085] The alignment and interaction steps may be repeated at predetermined time intervals for at least one reactor 180.

[0086] The method may further comprise, before placing the sample in the reactor 180, a step of calibrating the point sensor 150. The calibration may comprise a step of calibrating the signal as a function of the material, the thickness and the curvature of the bottom 184b of the reactor 180. The calibration may comprise, alternatively or in combination, a step of calibrating the point sensor 150 itself, for example if this point sensor 150 is not pre-calibrated. EXAMPLE

[0087] The present invention will be better understood by reading the following example which illustrates, without limitation, the use of the system.

[0088] In this example, the system 100 includes a support 120 comprising 2x3 locations 125, six magnetic stirring devices 140 positioned below the support 120, a transducer 160 positioned above the support 120 and a displacement device 165.

[0089] Each location 125 accommodates a reactor 180. The reactors 180 are round laboratory flasks made of borosilicate glass with a screw cap of the Duran Schott brand (registered trademark) with a volume of 133 mL. The reactors 180 are positioned vertically "upside down" so that the cap 182 is positioned under the bottom 184b.

[0090] Three test reactors 180 (RI, R2, R3) are filled with a sample containing a microbial inoculum and sodium acetate. The other three reactors 180 serve as controls. Two of them (R4, R5) contain only the same inoculum. microbial than the 180 test reactors while the third (R6) contains only sodium acetate (in the same quantity and concentration as RI, R2 and R3) in an abiotic medium.

[0091] The point sensor 150 present in each of the reactors 180 is configured to measure the oxygen level O2.

[0092] The interaction between the transducer 160 and the point sensor 150 is carried out by fluorescence. The transducer 160 used is the Electro-Optical Module E0M-02-FOM from Presens while the point sensor 150 is the PSt3 from Presens whose fluorescence intensity is linked to the dissolved oxygen concentration. The alignment of the transducer 160 and the reading of the oxygen level by fluorescence for each of the reactors 180 are carried out at regular intervals for nearly 4 days.

[0093] Figure 11 shows the evolution of the oxygen rate C (in percent) in the sample over time T (in days) for each of the reactors 180 (R1-R6).

[0094] First, we note that the oxygen level of the 180 control reactors (R4, R5, R6) remains stable (variation less than 2%) during the measurements. This clearly shows that the system according to presents a great stability which reduces the measurement bias.

[0095] Secondly, it is noted that the oxygen C level decreases in the three test reactors 180 (RI, R2, R3) around 1.5 days, 1.7 days and 2.3 days respectively. This decrease lasts between 0.2 days and 0.3 days. Then, the oxygen C level remains stable. This shows that sodium acetate is degraded quickly, the system according to the invention making it possible to obtain a precise and reliable measurement of the evolution of the oxygen C level and to precisely deduce the biodegradability of the sodium acetate sample. DIGITAL REFERENCES 100 - System / / 120 - Support / / 125 - Location / / 140 - Stirring Device / / 142 - Propeller / / 144 - Magnetic Attractor / / 146 - Actuator / / 148 - Magnetic Stirrer / / 150 - Point Sensor / / 160 - Transducer / / 165 - Stirring Device displacement / / 180 - Reactor / / 182 - Cap / / 184a - Side wall / / 184b - Bottom / / 190 - Applicator / / 192 - centering element / / 194 - positioning element / / F 1 - Propeller rotation / / F2 - Magnetic attractor rotation / / Al - Measuring axis / / A2 - Alignment axis UC - Oxygen level / / R1-R6 - Six different reactors for biodegradability measurement / / T - Time.

Claims

CLAIMS 1. A system (100) for measuring microbial activity comprising: At least one support (120), each support (120) comprising a plurality of locations (125) open upwards, each location (125) being configured to accommodate a reactor (180), each reactor (180) comprising a cap (182) adapted to be arranged in the location (125), preferably each location (125) is open upwards so as to position the bottom (184b) of the reactor (180) above the cap (182) of the reactor (180), each reactor (180) being adapted to hermetically contain a sample, each location (125) comprising a center defining a measurement axis (Al) perpendicular to the support; At least one stirring device (140) positioned under the support (120), each stirring device (140) being capable of stirring the sample in a reactor (180); At least one transducer (160) positioned above the support (120), each transducer (160) being configured, when aligned with the measurement axis (A1) of one of the locations (125) of the support, to interact with a point sensor (150) positioned inside a reactor (180) placed in said location (125), the point sensor (150) then being aligned with the measurement axis (A1), the point sensor (150) being configured to measure at least one marker of microbial activity; and A moving device (165) configured to move the at least one transducer (160) in order to successively align it on the measuring axis (Al) of several locations (125) of the support.

2. The microbial activity measurement system (100) according to claim 1, wherein each stirring device (140) comprises a movable magnetic attractor (144) positioned under a location (125) and capable of cooperating with a magnetic stirrer (148) disposed inside the reactor (180) placed in this location (125), the mobilization of the magnetic attractor (144) making it possible to mobilize the magnetic stirrer (148) in the reactor (180).

3. The microbial activity measurement system (100) according to any one of claims 1 to 2, wherein the transducer (160) allows interaction by fluorescence.

4. The microbial activity measurement system (100) according to any one of claims 1 to 3, wherein at least one of the microbial activity markers is chosen from the amount of oxygen, the amount of carbon dioxide, the amount of methane, the concentration of a predetermined chemical molecule, and / or the pressure inside the reactor (180).

5. A reactor (180) capable of hermetically containing a sample, the reactor (180) having a side wall (184a), a bottom (184b) and a ring on which a cap (182) fits, the ring being opposite the bottom (184b), the ring having an alignment axis (A2), a point sensor (150) being arranged inside the reactor (180), on the bottom (184b) of the reactor (180) and placed on the alignment axis (A2), the point sensor (150) being configured to measure at least one marker of microbial activity, the reactor (180) being capable of being accommodated in a location (125) of a support of the system (100) according to any one of claims 1 to 4 so that the cap (182) fits in the location (125) and so that the alignment axis (A2) overlaps with the measuring axis (Al) of said location (125).

6. The reactor (180) of claim 5, further comprising a magnetic stirrer (148) disposed within the reactor (180).

7. The reactor (180) according to claim 5 or 6, in which the bottom (184b) has a thickness of between 2 mm and 6 mm.

8. The reactor (180) according to any one of claims 5 to 7, in which the bottom (184b) has a curvature of between 600 mm and 3000 mm.

9. An applicator (190) for placing a point sensor (150) on the bottom (184b) of a reactor (180) in order to prepare a reactor (180) according to any one of claims 5 to 8, the applicator (190) comprising a centering element (192) adjustable on the ring of the reactor (180) and a positioning element (194) for placing the point sensor (150) on the bottom (184b) of the reactor (180) opposite the ring and on the alignment axis (A2).

10. A method of using a system (100) for measuring microbial activity according to any one of claims 1 to 4, the method comprising the steps of: Providing at least one reactor (180), the reactor (180) having a wall comprising a side wall (184a), a bottom (184b) and a ring onto which a plug (182) fits, the ring being opposite the bottom (184b), the ring having an alignment axis (A2); For each reactor (180): ■ Placement of at least one point sensor (150) configured to measure at least one microbial activity marker inside the reactor (180), on the bottom (184b) of the reactor and on the alignment axis (A2); ■ Introduction of a sample into the reactor (180); ■ Closing the reactor (180) with a cap (182); ■ Placing the reactor (180) in the support (120) by adjusting the plug (182) in one of the locations (125) of the support, such that the alignment axis (A2) overlaps with the measurement axis (Al) of said location (125), the bottom (184b) of the reactor (180) being positioned above the ring; Stirring the sample using the stirring device (140); Alignment of at least one of the transducers (160) with at least one of the measuring axes (Al) using the displacement device (165); Interaction of said transducer (160) with the point sensor (150) in order to measure at least one marker of microbial activity.

11. The method of use according to claim 10, wherein the reactor (180) is placed in the support (120), by fitting the plug (182) into one of the locations (125) of the support (120).

12. The method of use according to claim 11, wherein the bottom (184b) of the reactor (180) is positioned above the ring during placement of the reactor (180) in the holder (120).

13. The method of use according to any one of claims 10 to 12, wherein the alignment and interaction steps are repeated at predetermined time intervals for at least one reactor (180).

14. The method of use according to any one of claims 10 to 13, further comprising, before placing the sample in the reactor (180), a step of calibrating the point sensor (150).

15. The method of use according to any one of claims 10 to 14 allowing the measurement of the biodegradability of the sample, the sample comprising a microbial inoculum.

16. The method of use according to claim 15, wherein the point sensor (150) is configured to measure the amount of oxygen within the reactor (180).

17. The method of use according to claim 15 or 16, wherein the transducer (160) interacts with the point sensor (150) by fluorescence.

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