Control of metabolic pathways in a biological reactor

Abstract

The invention relates to a method for producing at least one molecule of interest by microbial communities which are placed in a bioreactor, the molecule of interest being produced by the consumption of carbon dioxide and dihydrogen by the microbial communities, the method comprising the following steps: • introducing an amount of carbon dioxide and an amount of dihydrogen into the bioreactor, the carbon dioxide being introduced at a first concentration enabling activation of a metabolic pathway for producing a first molecule of interest by at least one first microbial community; • determining a change in a concentration of carbon dioxide dissolved in the liquid phase; • adapting the amount of carbon dioxide introduced into the bioreactor on the basis of the change in the concentration of carbon dioxide dissolved in the liquid phase and on the basis of the molecule of interest which is to be produced.

Description

Control of metabolic pathways in a biological reactor

[0001] The invention relates to the production of organic molecules of interest in a bioreactor, more particularly by consumption of carbon dioxide and dihydrogen.

[0002] Methods for producing molecules of interest by microbial communities through the biological transformation of carbon dioxide corresponding to a set of biochemical reactions are already known in the state of the art. These reactions enable carbon dioxide and dihydrogen to be converted into several molecules of interest such as methane, volatile fatty acids (for example acetate), ethanol, or any other organic molecule comprising between one and eight carbon atoms.This biological process can be complex if the choice of using a mixed culture, i.e. a culture comprising several different microorganisms, is retained because: a set of microbial communities are present, whose metabolic pathways can produce a set of unwanted molecules and therefore reduce the performance of the production process, the ecological balance and kinetics of these microbial communities strongly depend on the operating conditions applied in the biological process such as temperature, pH, bioreactor feeding mode and substrate distribution, and a balance must be found between the different microbial communities in order to produce the targeted molecule of interest. It should be noted that these groups of microorganisms are in interaction with each other, with competition phenomena with regard to the availability of carbon dioxide and dihydrogen.

[0003] In a mixed culture methanation process, three reaction pathways (using carbon dioxide for the first two of them) are particularly known: the hydrogenotrophic pathway, allowing the production of methane and water by consumption of carbon dioxide and dihydrogen, the homoacetogenic pathway, allowing the production of acetate and water by consumption of carbon dioxide and dihydrogen, and the acetoclastic pathway allowing the production of methane and water by consumption of acetate from the homoacetogenic pathway.

[0004] In order to improve the production of a molecule of interest, several options have already been considered, namely: Improving gas transfer: this involves improving the solubility of dihydrogen, for example by carrying out significant bubbling in the bioreactor in addition to the application of high pressure in the bioreactor enclosure. This would maximize the gas / liquid transfer of dihydrogen. However, such a solution to improve gas transfer does not allow for the control of microbial communities. Indeed, no management of metabolic pathways is carried out and, if the operating conditions are favorable, several unwanted molecules can be produced at the same time and therefore reduce the production yields for a target molecule. Using a pure culture: in order to ensure optimal production of a targeted molecule of interest, the use of a pure culture (i.e.culture comprising only one type of microorganism) can be applied. For this, several species have been selected such as Methanothermobacter thermoautotrophicus in the case of a thermophilic process for the production of methane, or Acetobacterium woodii for the production of acetate. However, and although this method is effective in avoiding competition between microbial communities for access to carbon dioxide and dihydrogen, it leads to the need to work in sterile conditions with a higher risk of contamination. In addition, the process is often not very robust, not very flexible, and generally costs more. The establishment and indirect control of a ratio of the partial pressure of dihydrogen and carbon dioxide greater than 5: 1 by controlling the volume of injected gas. This is to obtain, in the bioreactor, optimal conditions for the production of a molecule of interest.However, this solution does not allow for a certain flexibility in the production of molecules of interest. In addition, the monitoring of the process performance and in particular the consumption of dihydrogen and carbon dioxide is carried out by measuring the gas mixture at the outlet of the bioreactor. This measurement does not allow us to know the actual state of the bioreactor at the time of the measurement, but its past state. Therefore, it is dangerous to control the production of a molecule of interest, because the supply of dihydrogen and carbon dioxide to the bioreactor, if it takes place, is based on a measurement that does not reflect the current state of the bioreactor.

[0005] In the event of a bioreactor drift, it is difficult to rebalance it. The latter is then stopped, either to allow it to stabilize (this can take several days), or to completely restart the operation of producing a molecule of interest.

[0006] The invention aims in particular to provide a method for producing molecules of interest by microbial communities in mixed culture placed in a bioreactor, making it possible to finely control the production of molecules of interest by at least one bacterial community, while offering the possibility of easy transition from the production of one molecule of interest to another.

[0007] To this end, the subject of the invention is a method for producing at least one molecule of interest by microbial communities placed in a bioreactor comprising a liquid phase, the production of the molecule of interest being obtained by consumption of carbon dioxide and dihydrogen by the microbial communities, the method comprising the following steps: introduction of a quantity of carbon dioxide and a quantity of dihydrogen into the bioreactor, the carbon dioxide being introduced at a first concentration allowing activation of a metabolic pathway for the production of a first molecule of interest by at least one first microbial colony, determination of a change in a concentration of carbon dioxide dissolved in the liquid phase,adaptation of the quantity of carbon dioxide introduced into the bioreactor according to the evolution of the concentration of carbon dioxide dissolved in the liquid phase and according to the molecule of interest whose production is desired.,

[0008] Using such a method, it is possible to very precisely control the carbon dioxide concentration in the bioreactor by directly measuring the carbon dioxide dissolved in the liquid phase. This measurement, reflecting the state of the bioreactor at time T, makes it possible to control the introduction of carbon dioxide to obtain an optimal concentration for the activation of a microbial community for the production of a molecule of interest (the activation of a microbial community depends at least in part on the carbon dioxide concentration of the liquid phase). This results in a reliable and robust production process over the duration of the production process.

[0009] Furthermore, and by having precise knowledge of the carbon dioxide concentration in the bioreactor, it is possible, and easy, to quickly vary the carbon dioxide concentration in the bioreactor so as to switch from the production of a first molecule of interest by a first microbial community to that of a second molecule of interest by a second microbial community. This results in a flexible process in terms of adapting the bioreactor to the production of different molecules of interest.

[0010] The production method according to the invention may further comprise at least one of the following characteristics: the quantity of carbon dioxide introduced into the bioreactor as a function of the change in a concentration of carbon dioxide dissolved in the liquid phase is determined so as to substantially ensure maintenance of the first concentration of carbon dioxide in the bioreactor; the first concentration of carbon dioxide is greater than 2 mmol / L; the quantity of carbon dioxide introduced into the bioreactor as a function of the change in a concentration of carbon dioxide dissolved in the liquid phase is determined so as to obtain a second concentration of carbon dioxide dissolved in the liquid phase, the second concentration of carbon dioxide dissolved in the liquid phase allowing activation of a metabolic pathway for the production of a second molecule of interest by at least a second microbial community;the second carbon dioxide concentration is less than or equal to 2 mmol / L; the molecules of interest are chosen from methane, volatile fatty acids, for example acetate, propionate, butyrate, isobutyrate, 2-methylbutyrate, valerate, isovalerate, caproate, caprylate, butanol, isobutanol; the microbial communities are present in the liquid phase and / or on at least one membrane forming a biofilm support; carbon monoxide is introduced into the bioreactor in addition to the introduction of carbon dioxide and dihydrogen; bubbles are generated during the introduction of carbon dioxide and dihydrogen; sodium bicarbonate is introduced into the bioreactor; at least one of the following parameters is monitored: pH of the liquid phase, gaseous composition at the bioreactor outlet, electrical conductivity of the dissolved phase;the production method comprises a step of separating suspended matter from the liquid phase, for example by a granulometric and / or gravimetric separation device; andthe production method comprises a step of separating volatile fatty acids by electrodialysis, reverse or direct osmosis, and / or removal of water by distillation under vacuum or not.;

[0011] The invention also relates to a device for producing at least one molecule of interest by microbial communities, the production of molecules of interest being obtained by consumption of carbon dioxide and dihydrogen by the microbial communities, the device comprising:A bioreactor configured to accommodate a liquid phase and several microbial communities,at least one member for introducing a quantity of carbon dioxide and a quantity of dihydrogen into the bioreactor configured to introduce the carbon dioxide at at least a first concentration allowing activation of a metabolic pathway for producing a first molecule of interest by at least a first microbial community,at least one member for determining the evolution of a concentration of carbon dioxide dissolved in the liquid phase,at least one member for determining a quantity of carbon dioxide introduced into the bioreactor by the introduction member as a function of the change in a concentration of carbon dioxide dissolved in the liquid phase and as a function of the molecule of interest whose production is desired.,

[0012] The production device according to the invention may further comprise at least one of the following characteristics: the production device comprises separate devices for introducing carbon dioxide and dihydrogen; the introduction member is configured to obtain a second concentration of carbon dioxide in the bioreactor, the second concentration of carbon dioxide dissolved in the liquid phase allowing activation of a metabolic pathway for producing a second molecule of interest by at least one second microbial community; the production device comprises at least one member for introducing carbon monoxide into the bioreactor; the production device comprises at least one bubble generation member configured to generate bubbles during the introduction of carbon dioxide and dihydrogen; the production device comprises at least one member for introducing sodium bicarbonate into the bioreactor;the production device comprises at least one member for measuring at least one of the following parameters: pH of the liquid phase, gaseous composition at the bioreactor outlet, electrical conductivity of the dissolved phase; and the production device comprises at least one member for separating suspended matter from the liquid phase, for example by a granulometric and / or gravimetric separation device.; Brief description of the figures

[0013] The invention will be better understood on reading the following description, given solely by way of example and with reference to the appended drawings in which:

[0014] is a schematic representation of a method for producing at least one molecule of interest according to the invention,

[0015] is a representation of the concentrations of dissolved carbon dioxide in a medium obtained between a calculation via the partial pressure of carbon dioxide (according to Henry's law via the measurement of carbon dioxide in gaseous form in the reactor) and a direct measurement of the dissolved carbon dioxide in a medium,

[0016] is a representation of the evolution of the concentration of volatile fatty acids as a function of the concentration of carbon dioxide dissolved in a medium, and

[0017] is a representation of the evolution of methane concentration as a function of the concentration of dissolved carbon dioxide in a medium. Detailed description

[0018] Reference is now made to the schematically representing a process for the production of at least one molecule of interest by microbial communities (typically anaerobic microorganisms containing hydrogenotrophic methanogens, acetoclast methanogens and homoacetogens, for example digested sludge) placed in a bioreactor comprising a liquid phase, the production of the molecule of interest being obtained by consumption of carbon dioxide and dihydrogen by the microbial communities.

[0019] The first step 2 consists of introducing several microbial communities into a bioreactor in order to obtain a mixed culture in the bioreactor. These can be contained in the liquid phase of the bioreactor and / or on one or more membranes forming a biofilm support in contact with the liquid phase, the bioreactor including a recirculation of the liquid phase. Of course, the choice of the microbial communities introduced depends on the nature of the molecule(s) of interest that one wishes to produce using the bioreactor. The microbial communities all share a possibility of activation in the presence of a certain concentration of carbon dioxide. This allows for the recovery of carbon dioxide but also carbon monoxide in a controlled environment.

[0020] Following step 2, a second step 4 consists of introducing a quantity of carbon dioxide and a quantity of dihydrogen into the bioreactor, the carbon dioxide being introduced at a first concentration allowing activation of a metabolic pathway for the production of a first molecule of interest by at least one first microbial community. In other words, operating conditions favorable to the production of a first molecule of interest via at least one microbial community are created in the bioreactor. The supply of carbon dioxide and dihydrogen may be continuous or intermittent and may be carried out at atmospheric pressure. The source of carbon dioxide may be a set of gases (syngas, biogas, gases from industries).

[0021] Following step 4, an evolution of a concentration of carbon dioxide dissolved in the liquid phase is determined (step 6). Indeed, microbial communities are sensitive to the concentration of carbon dioxide in the liquid phase, as will be illustrated later. Therefore, direct control of the evolution of the carbon dioxide concentration makes it possible to control the introduction of carbon dioxide to obtain an optimal concentration for the activation of a microbial community for the production of a molecule of interest (the activation of a microbial community depends at least in part on the concentration of the carbon dioxide phase). This results in a reliable and robust production process over the duration of the production process. This determination step preferably aims to directly control all the forms of carbon dioxide dissolved in the liquid phase (CO2, HCO 3- , CO3 2-). This method allows in particular to be more precise than the measurement of the partial pressure of carbon dioxide which is not suitable in the case of rapid consumption kinetics and is therefore not able to faithfully represent the variations in concentration in solution, linked to Henry's law. This is visible on the where we observe a discrepancy between a measurement of dissolved carbon dioxide according to Henry's law (curve 12) and the direct measurement of dissolved carbon dioxide (curve 14).

[0022] Following step 6, the amount of carbon dioxide introduced into the bioreactor is adjusted according to the change in the concentration of carbon dioxide dissolved in the liquid phase and according to the molecule of interest whose production is desired. The aim of this step is to achieve rapid and precise control of the carbon dioxide concentration. This allows, as we will describe later, to choose the activation of one microbial community or another and therefore to choose the production of one molecule of interest or another.

[0023] During the step of adapting the quantity of carbon dioxide introduced into the bioreactor as a function of the change in the concentration of carbon dioxide dissolved in the liquid phase and as a function of the molecule of interest whose production is desired, two scenarios emerge: According to a first scenario (step 8), the quantity of carbon dioxide introduced into the bioreactor as a function of the change in a concentration of carbon dioxide dissolved in the liquid phase is determined so as to substantially ensure maintenance of the first concentration of carbon dioxide in the bioreactor. This reflects a desire to maintain the production of the first molecule of interest via at least one microbial community.In such a case, the repeated repetition of the step of determining the change in a concentration of dissolved carbon dioxide in the liquid phase consists of ensuring that the first concentration of carbon dioxide in the bioreactor is maintained. There is therefore a repetition of the steps of determining a change in a concentration of dissolved carbon dioxide in the liquid phase and of adapting the quantity of carbon dioxide introduced into the bioreactor according to the change in a concentration of dissolved carbon dioxide in the liquid phase to substantially maintain the first concentration. For example, the first concentration may be greater than 2 mmol / L.Such a concentration allows, for example, the production of methane by one or more microbial communities (activation of the hydrogenotrophic pathway and possibly the acetoclastic pathway (in the presence of volatile fatty acids in the liquid phase and consumed to form methane)). This is visible on the: in fact, we observe that a passage of the carbon dioxide concentration above a value of 2 mmol / L (curve 16) leads, a few seconds or a few tens of seconds later, to an increase in the production of methane, visible by an increase in the methane concentration (curve 18). In contrast, a passage of the carbon dioxide concentration below a value of 2 mmol / L leads, a few seconds or a few tens of seconds later, to a decrease or even a stop in the production of methane.According to a second scenario (step 10), the quantity of carbon dioxide introduced into the bioreactor as a function of the evolution of a concentration of carbon dioxide dissolved in the liquid phase is determined so as to obtain a second concentration of carbon dioxide dissolved in the liquid phase, the second concentration of carbon dioxide dissolved in the liquid phase allowing an activation of a metabolic pathway for the production of a second molecule of interest by at least a second microbial community. This reflects a desire to modify the production of molecules of interest via at least one microbial community.In such a case, the repeated repetition of the step of determining the change in a concentration of carbon dioxide dissolved in the liquid phase consists of ensuring a change from the first concentration of carbon dioxide in the bioreactor to a second concentration in the bioreactor, then ensuring that this second concentration is maintained. There is therefore a repetition of the steps of determining a change in a concentration of carbon dioxide dissolved in the liquid phase and of adapting the quantity of carbon dioxide introduced into the bioreactor according to the change in a concentration of carbon dioxide dissolved in the liquid phase with the aim of modifying the molecule of interest produced by the bioreactor. For example, the second concentration may be less than or equal to 2 mmol / L.Such a concentration allows, for example, the production of volatile fatty acids, for example acetate, by one or more microbial communities, by activation of the homoacetogenic pathway. This is visible on the: in fact, we observe that a passage of the carbon dioxide concentration above a value of 2 mmol / L (curve 20) leads, a few seconds or a few tens of seconds later, to a reduction or even a stop in the production of volatile fatty acids (curve 22). In contrast, a passage of the carbon dioxide concentration below a value of 2 mmol / L leads, a few seconds or a few tens of seconds later, to an increase in the production of volatile fatty acids.

[0024] Figures 2 to 4 were obtained by performing tests in a laboratory reactor comprising liquid phase recirculation and injection of dihydrogen via a diffusion membrane and carbon dioxide injection by a micro-bubbling system directly into the bioreactor. The temperature of the liquid phase was kept constant at 37°C. Anaerobic sludge recirculation is maintained by a peristaltic pump from the bottom to the top of the reactor containing a diffusion membrane. The pH, temperature and conductivity of the sludge were measured online, respectively, continuously. The temperature of the liquid phase was kept constant by an external enclosure allowing the recirculation of hot water. An injection of carbon dioxide and dihydrogen, subsequently mixed if necessary in a mixing chamber at the desired ratio before being continuously injected into the reactor, is planned.For each gas, a gas flow meter was used to define the respective gas flow rate. The outgoing gas was quantified by a flow meter. The liquid medium used can be from an anaerobic digester for wastewater treatment. The sludge is previously diluted to obtain a concentration of 10 g / L and sieved with a 3.15 millimeter sieve. A micronutrient solution was added (1 mL / L) composed of 0.5 g / L EDTA (ethylenediaminetetraacetic acid); 2 g / L FeCl2.4H2O; 50 mg / LH3BO3; 50 mg / L ZnCl2; 40 mg / L CuCl2.2H2O; 50 mg / L MnCl2.4H2O; 50 mg / L (NH4)6Mo7O24.4H2O; 50 mg / L AlCl3; 50 mg / L CoCl2.6H2O; 100 mg / L NiCl2.6H2O; 100 mg / L Na2SeO3.5H2O. A phosphate buffer is also used at a concentration of 20 mL / L.

[0025] Generally, the molecules of interest can be chosen from methane, volatile fatty acids, for example acetate, propionate, butyrate, isobutyrate, 2-methylbutyrate, valerate, isovalerate, caproate, caprylate, butanol, isobutanol.

[0026] Advantageously, carbon monoxide is introduced into the bioreactor in addition to the introduction of carbon dioxide and dihydrogen. The introduction of carbon monoxide allows a supply of carbon by valorizing this gas. The latter also allows the activation of an additional reaction pathway carried out by carboxydotrophic acetogens thanks to an enzyme called "CO dehydrogenase" allowing the production of acetate and carbon dioxide by consumption of carbon monoxide and water.

[0027] Advantageously, bubbles are generated when carbon dioxide and hydrogen are introduced. This facilitates gas / liquid transfer to dissolve carbon dioxide and hydrogen more quickly and make them available to the microbial community(ies) consuming them.

[0028] Advantageously, sodium bicarbonate is introduced into the bioreactor. This allows carbon dioxide to be introduced in a form other than gaseous, which eliminates potential problems related to gas / liquid transfer.

[0029] It is also possible to control at least one of the following parameters: pH of the liquid phase, gas composition at the bioreactor outlet, electrical conductivity of the dissolved phase. Regarding pH control, the invention could have an impact on the pH of the liquid phase, a parameter that is essential for the stability of a biological reactor. Indeed, the invention is based on the concentration of carbon dioxide dissolved in the liquid phase, which can be transformed into carbonic acid (H2CO3) or even bicarbonate ion (HCO3 -), two acid molecules. Thus, by controlling the dissolved carbon dioxide, the pH can be modified, which can affect the microbial communities present. The risk lies in an excessive variation in pH creating instability in the process. However, according to the inventors' experiments, the pH remains in an ideal range for the microbial communities and does not make the process unstable. Measuring the gas composition allows us to know the performance of the process (consumption rate of carbon dioxide and dihydrogen, production of methane). Measuring the conductivity is an indirect measurement of dissolved carbon dioxide.

[0030] It is possible for the method according to the invention to comprise a step of separating suspended matter from the liquid phase (step 11), for example by a granulometric and / or gravimetric separation device. It is also possible to provide a fine separation on the soluble part to increase the concentration of volatile fatty acids by electrodialysis, reverse or direct osmosis or even by removing water by distillation (under vacuum or not).

[0031] The invention also relates to a device for producing at least one molecule of interest by microbial communities, the production of molecules of interest being obtained by consumption of carbon dioxide and dihydrogen by the microbial communities, the device comprising. The latter comprises a bioreactor configured to accommodate a liquid phase and several microbial communities. The bioreactor is a conventional bioreactor and will not be described in detail subsequently.

[0032] The device also comprises at least one member for introducing a quantity of carbon dioxide and a quantity of dihydrogen into the bioreactor configured to introduce the carbon dioxide at at least a first concentration allowing activation of a metabolic pathway for producing a first molecule of interest by at least a first microbial community. This introduction member is for example controlled by an electronic control unit configured to obtain a precise quantity of injected gas.

[0033] The device also comprises at least one member for determining the change in a concentration of carbon dioxide dissolved in the liquid phase (for example a measuring probe), and at least one member for determining a quantity of carbon dioxide introduced into the bioreactor by the introduction member as a function of the change in a concentration of carbon dioxide dissolved in the liquid phase and as a function of the molecule of interest whose production is desired. This may be a conventional gas analyzer. Alternatively, it is possible to use a gas source whose gas content is known.

[0034] Advantageously, the device for producing at least one molecule of interest by microbial communities comprises separate devices for introducing carbon dioxide and dihydrogen. This allows for refined control of the injection of these two elements.

[0035] The introduction member can be configured to obtain a second concentration of carbon dioxide in the bioreactor, the second concentration of carbon dioxide dissolved in the liquid phase allowing activation of a metabolic pathway for the production of a second molecule of interest by at least a second microbial community, as explained above.In such a case, the member for determining the evolution of a concentration of carbon dioxide dissolved in the liquid phase makes it possible to obtain evolution data sent to the electronic control unit which, via the member for determining a quantity of carbon dioxide introduced into the bioreactor by the introduction member as a function of the evolution of a concentration of carbon dioxide dissolved in the liquid phase and as a function of the molecule of interest whose production is desired, adjusts the quantity of carbon dioxide injected by the introduction member.

[0036] The device may further comprise at least one member for introducing carbon monoxide into the bioreactor (for example of the same type as the member for introducing carbon dioxide and dihydrogen), at least one bubble generation member configured to generate bubbles during the introduction of carbon dioxide and dihydrogen or at least one member for introducing sodium bicarbonate (a pump) into the bioreactor for the reasons mentioned above.

[0037] The device may also include at least one member measuring at least one of the following parameters: pH of the liquid phase, gas composition at the bioreactor outlet, conductivity, for the reasons mentioned above.

[0038] Finally, and still for the reasons mentioned above, the device may comprise at least one member for separating suspended matter from the liquid phase, for example by a granulometric and / or gravimetric separation device.

[0039] The process according to the invention can be coupled with another process for transforming acetate for the production of other value-added molecules by biological and / or chemical means such as chain elongation for the production of volatile fatty acids (propionate, butyrate, caproate, etc.). List of references

[0040] 2: introduction of several microbial communities into a bioreactor

[0041] 4: introduction of a quantity of carbon dioxide and a quantity of dihydrogen into the bioreactor

[0042] 6: determination of an evolution of a concentration of carbon dioxide dissolved in the liquid phase

[0043] 8: maintaining carbon dioxide concentration

[0044] 10: change in carbon dioxide concentration

[0045] 11: step of separation of suspended matter from the liquid phase

[0046] 12: Curve of dissolved carbon dioxide measurement according to Henry's law

[0047] 14: curve of direct measurement of dissolved carbon dioxide in the liquid phase

[0048] 16, 20: curve showing the evolution of the concentration of dissolved carbon dioxide

[0049] 18: curve showing the evolution of methane concentration

[0050] 22: curve of the evolution of the concentration of volatile fatty acids

Claims

Method for producing at least one molecule of interest by microbial communities placed in a bioreactor comprising a liquid phase, the production of the molecule of interest being obtained by consumption of carbon dioxide and dihydrogen by the microbial communities, the method comprising the following steps:Introduction (4) of a quantity of carbon dioxide and a quantity of dihydrogen into the bioreactor, the carbon dioxide being introduced at a first concentration allowing activation of a metabolic pathway for the production of a first molecule of interest by at least one first microbial community,Determination (6) of a change in a concentration of carbon dioxide dissolved in the liquid phase,Adaptation (8,10) the quantity of carbon dioxide introduced into the bioreactor as a function of the change in the concentration of carbon dioxide dissolved in the liquid phase and as a function of the molecule of interest whose production is desired., Production method according to claim 1, in which the quantity of carbon dioxide introduced into the bioreactor as a function of the evolution of a concentration of carbon dioxide dissolved in the liquid phase is determined so as to substantially ensure maintenance of the first concentration of carbon dioxide in the bioreactor. Production method according to the preceding claim, wherein the first carbon dioxide concentration is greater than 2 mmol / L. Production method according to claim 1, in which the quantity of carbon dioxide introduced into the bioreactor as a function of the evolution of a concentration of carbon dioxide dissolved in the liquid phase is determined so as to obtain a second concentration of carbon dioxide dissolved in the liquid phase, the second concentration of carbon dioxide dissolved in the liquid phase allowing activation of a metabolic pathway for the production of a second molecule of interest by at least a second microbial community. Production method according to the preceding claim, wherein the second carbon dioxide concentration is less than or equal to 2 mmol / L. Production method according to any one of the preceding claims, in which carbon monoxide is introduced into the bioreactor in addition to the introduction of carbon dioxide and dihydrogen. Production method according to any one of the preceding claims, in which sodium bicarbonate is introduced into the bioreactor. Device for producing at least one molecule of interest by microbial communities, the production of molecules of interest being obtained by consumption of carbon dioxide and dihydrogen by the microbial communities, the device comprising:A bioreactor configured to accommodate a liquid phase and several microbial communities,at least one member for introducing a quantity of carbon dioxide and a quantity of dihydrogen into the bioreactor configured to introduce the carbon dioxide at at least a first concentration allowing activation of a metabolic pathway for producing a first molecule of interest by at least a first microbial community,at least one member for determining the evolution of a concentration of carbon dioxide dissolved in the liquid phase,at least one member for determining a quantity of carbon dioxide introduced into the bioreactor by the introduction member as a function of the change in a concentration of carbon dioxide dissolved in the liquid phase and as a function of the molecule of interest whose production is desired., Production device according to the preceding claim, comprising separate devices for introducing carbon dioxide and dihydrogen. Production device according to any one of claims 8 or 9, wherein the introduction member is configured to obtain a second concentration of carbon dioxide in the bioreactor, the second concentration of carbon dioxide dissolved in the liquid phase allowing activation of a metabolic pathway for the production of a second molecule of interest by at least a second microbial community. Production device according to any one of claims 8 to 10, comprising at least one member for introducing carbon monoxide into the bioreactor.

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