Novel iron-oxidizing bacterium, material containing the iron-oxidizing bacterium, and method for removing arsenic from arsenic-containing liquid using the iron-oxidizing bacterium

Abstract

To provide an iron-oxidizing bacterium that enables efficient removal of arsenic (especially, arsenite and arsenate) from an arsenic-containing liquid, a material containing the iron-oxidizing bacterium, and a method for removing arsenic from an arsenic-containing liquid using the iron-oxidizing bacterium.SOLUTION: An iron-oxidizing bacterium is capable of oxidizing ferrous ions to ferric ions and oxidizing arsenite to arsenate. A material containing the iron-oxidizing bacterium further comprises a support material suitable for habitation of the iron-oxidizing bacterium. A method for removing arsenic from an arsenic-containing liquid using the iron-oxidizing bacterium includes: a bacterium addition step; a reaction step including formation of ferric hydroxide (iron(III) hydroxide) minerals capable of adsorbing arsenite and arsenate, and bacterium-mediated oxidation of arsenite to arsenate; and a separation step of separating ferric hydroxide minerals having adsorbed arsenite and / or arsenate from the arsenic-containing liquid.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a novel iron-oxidizing bacterium, a material containing the iron-oxidizing bacterium, and a method for removing arsenic in an arsenic-containing liquid using the iron-oxidizing bacterium.

Background Art

[0002] Arsenic is highly harmful, and even if ingested in trace amounts for a long time, it is known to cause health problems due to chronic arsenic poisoning such as skin diseases like keratosis, carcinogenesis, metabolic diseases, neurological diseases, and immune diseases. Therefore, it is necessary to reduce the arsenic concentration contained in wastewater, soil, etc. to an appropriate value. Arsenic mainly exists in environmental water in the trivalent form (arsenous acid) and the pentavalent form (arsenic acid), and both of these forms exist as oxyanions. In particular, arsenous acid is known to have low solid adsorbability to minerals, etc. (i.e., it is easily diffused in water) and high biotoxicity.

[0003] As a method for removing arsenic dissolved in water, for example, a removal method using a heavy metal adsorbent containing manganese oxide produced by microorganisms and an anion adsorbent that adsorbs anions containing arsenic in the pentavalent form is known (see Patent Document 1). According to this removal method, trivalent arsenic (arsenous acid) in the environment, which is difficult to remove by adsorption, is oxidized by the oxidizing power of manganese oxide (i.e., inorganic oxidation) to arsenic in the pentavalent form with high solid adsorbability (arsenic acid), and this pentavalent arsenic is adsorbed and removed by the anion adsorbent.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the case of the invention described in Patent Document 1, a method is adopted in which arsenic in the trivalent form is oxidized to arsenic in the pentavalent form by the oxidizing power of manganese oxide (vernadite). However, since manganese oxide and trivalent arsenic have negative charges, they repel each other, and there is a drawback that it is difficult for the oxidation of trivalent arsenic to pentavalent arsenic to proceed. Further, since manganese oxide itself does not have a strong adsorbing ability for trivalent and pentavalent arsenic, there is a drawback that iron oxide or an iron oxide source (iron powder) as an arsenic adsorbent is further required.

[0006] An object of the present invention made in view of the above problems is to provide bacteria capable of more efficiently removing arsenic in an arsenic-containing liquid than in the past, a material containing the bacteria, and a method for removing arsenic in an arsenic-containing liquid using the bacteria.

Means for Solving the Problems

[0007] As a result of intensive studies to achieve the above object, the present inventors have found that it is possible to efficiently remove arsenic in an arsenic-containing liquid by using bacteria collected and isolated at a certain place in Japan, and have completed the present invention. Furthermore, as a result of detailed analysis of this bacterium, it has been found that this bacterium is a new species of bacterium having a function different from known bacteria.

[0008] The iron-oxidizing bacterium of the invention according to claim 1 for achieving the above object is characterized by having the ability to oxidize divalent iron ions to trivalent iron ions and the ability to oxidize arsenous acid to arsenic acid.

[0009] The invention according to claim 2 is characterized in that, in the invention according to claim 1, the iron-oxidizing bacterium is a bacterium belonging to the genus Roseovarius.

[0010] The invention according to claim 3 is the invention according to claim 2, characterized in that, with respect to Roseovarius azorensis, the Digital DNA-DNA Hybridization of the iron-oxidizing bacterium is 20-40%, and the Average Nucleotide Identity of the iron-oxidizing bacterium is 70-90%.

[0011] The invention according to claim 4 is the invention according to claim 2, characterized in that the iron-oxidizing bacterium is Roseovarius sp. OM2 strain.

[0012] The material of the invention according to claim 5 is characterized by comprising the iron-oxidizing bacterium according to any one of claims 1 to 4 and a support material on which the iron-oxidizing bacterium can inhabit.

[0013] The method for removing arsenic in the arsenic-containing liquid of the invention according to claim 6 is an addition step of adding an iron-oxidizing bacterium having the ability to oxidize ferrous ions to ferric ions and the ability to oxidize arsenous acid to arsenic acid according to any one of claims 1 to 4, or a mixture of an iron-oxidizing bacterium having the ability to oxidize ferrous ions to ferric ions and a bacterium having the ability to oxidize arsenous acid to arsenic acid into the arsenic-containing liquid, a reaction step including that the iron-oxidizing bacterium having the ability to oxidize ferrous ions to ferric ions and the ability to oxidize arsenous acid to arsenic acid or the iron-oxidizing bacterium having the ability to oxidize ferrous ions to ferric ions contacts with ferrous ions to form an iron(III) hydroxide mineral capable of adsorbing arsenous acid and arsenic acid, and arsenous acid is adsorbed on the iron(III) hydroxide mineral, and the iron-oxidizing bacterium having the ability to oxidize ferrous ions to ferric ions and the ability to oxidize arsenous acid to arsenic acid or the bacterium having the ability to oxidize arsenous acid to arsenic acid oxidizes arsenous acid to arsenic acid, and a separation step of separating the iron(III) hydroxide mineral adsorbed with arsenous acid and / or arsenic acid from the arsenic-containing liquid, and is characterized by including the above.

Advantages of the Invention

[0014] According to the iron-oxidizing bacteria of the present invention, a material containing the iron-oxidizing bacteria, and a method for removing arsenic in an arsenic-containing liquid using the iron-oxidizing bacteria, arsenic (particularly, arsenous acid and arsenic acid) can be efficiently removed from the arsenic-containing liquid.

Brief Description of the Drawings

[0015]

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Embodiments for Carrying Out the Invention

[0016] [Overview of the Arsenic Removal Mechanism Using Iron-Oxidizing Bacteria of the Present Invention] Figure 1 shows an overview of the arsenic removal mechanism using iron-oxidizing bacteria of the present invention. The iron-oxidizing bacteria of the present invention have both the function of oxidizing divalent iron ions to trivalent iron ions and the function of oxidizing arsenous acid (arsenic in the trivalent form) to arsenic acid (arsenic in the pentavalent form). Due to the function of oxidizing divalent iron ions to trivalent iron ions among these functions, divalent iron ions in the arsenic-containing liquid are oxidized to trivalent iron ions. By this oxidation, a mineral containing iron(III) hydroxide is formed on the surface of the iron-oxidizing bacteria. Arsenous acid in the arsenic-containing liquid is adsorbed onto this mineral containing iron(III) hydroxide, and arsenous acid is oxidized to arsenic acid by the ability of the iron-oxidizing bacteria of the present invention to oxidize arsenous acid to arsenic acid. Note that by this oxidation, highly toxic arsenous acid is oxidized to less toxic arsenic acid, so detoxification can also be achieved. In this way, arsenic in the arsenic-containing liquid is removed by adsorbing arsenic (arsenous acid and arsenic acid) onto the mineral containing iron(III) hydroxide formed by the iron-oxidizing bacteria of the present invention.

[0017] [Iron-Oxidizing Bacteria of the Present Invention] The iron-oxidizing bacteria of the present invention have the ability to oxidize divalent iron ions to trivalent iron ions and the ability to oxidize arsenous acid to arsenic acid.

[0018] The iron-oxidizing bacteria preferably belong to the genus Roseovarius bacteria, more preferably Roseovarius sp. OM2 strain. This Roseovarius sp. OM2 strain was deposited as NITE AP-03992 on October 18, 2023 (receiving date) at the Patent Microorganisms Depositary, National Institute of Technology and Evaluation.

[0019] The Roseovarius sp. OM2 strain has, for example, a lower limit of DDH (Digital DNA-DNA Hybridization) with respect to Roseovarius azorensis SSW084 KC534172 that is preferably 15% or more, more preferably 20% or more, and even more preferably 25% or more, and an upper limit that is preferably 45% or less, more preferably 40% or less, and even more preferably 35% or less. These lower and upper limits can be arbitrarily combined. This DDH is particularly 29%. And the Roseovarius sp. OM2 strain has, for example, a lower limit of ANI (Average Nucleotide Identity) with respect to Roseovarius azorensis SSW084 KC534172 that is preferably 70% or more, more preferably 75% or more, and even more preferably 80% or more, and an upper limit that is preferably 90% or less, more preferably 85% or less. These lower and upper limits can be arbitrarily combined. This ANI is particularly 83%.

[0020] [Material containing the iron-oxidizing bacteria of the present invention] A material containing the iron-oxidizing bacteria of the present invention can be provided. In addition to the iron-oxidizing bacteria of the present invention, this material contains a support material on which the bacteria can inhabit. As this support material, known support materials (for example, porous filter materials, filter paper, and felt) that can provide a living environment for the bacteria can be used. Therefore, the material containing the iron-oxidizing bacteria of the present invention can be used, for example, as a filter material (for example, porous filter materials, filter paper, and felt).

[0021] For inoculating the iron-oxidizing bacteria onto the support material, known inoculation methods can be used.

[0022] [Method for removing arsenic in an arsenic-containing liquid using the iron-oxidizing bacteria of the present invention] The method for removing arsenic in an arsenic-containing liquid using iron-oxidizing bacteria includes an addition step, a reaction step, and a separation step, which will be described later.

[0023] (Object to be treated) The arsenic-containing liquid to be treated is preferably an arsenic-containing liquid (arsenic-containing aqueous liquid) mainly composed of water, and examples thereof include raw water, drinking water, and mine wastewater. This arsenic-containing liquid contains, for example, arsenous acid and optionally arsenic acid, and further preferably contains iron (ferrous ions, or ferrous ions and ferric ions).

[0024] The arsenic-containing liquid is preferably in an environment containing oxygen (i.e., an aerobic environment). The oxygen concentration of the arsenic-containing liquid is not limited, but the oxygen concentration is preferably 20 to 250 μM, more preferably 100 to 200 μM.

[0025] (Addition step) In the addition step, iron-oxidizing bacteria having the ability to oxidize ferrous ions of the present invention to ferric ions and the ability to oxidize arsenous acid to arsenic acid are added to the arsenic-containing liquid. Instead of the iron-oxidizing bacteria having the ability to oxidize ferrous ions of the present invention to ferric ions and the ability to oxidize arsenous acid to arsenic acid, a mixture of bacteria having the ability to oxidize ferrous ions to ferric ions and bacteria having the ability to oxidize arsenous acid to arsenic acid can also be used. In this case, examples of the iron-oxidizing bacteria having the ability to oxidize ferrous ions to ferric ions include bacteria of the genus Gallionella or Leptothrix, and examples of the bacteria having the ability to oxidize arsenous acid to arsenic acid include bacteria of the genus Mesorhizobium or Thiomonas.

[0026] The addition of the iron-oxidizing bacteria having the ability to oxidize ferrous ions of the present invention to ferric ions and the ability to oxidize arsenous acid to arsenic acid (or a mixture of bacteria having the ability to oxidize ferrous ions to ferric ions and bacteria having the ability to oxidize arsenous acid to arsenic acid) to the arsenic-containing liquid can be carried out, for example, by previously performing the operation of statically culturing the bacteria and then adding the bacteria to the arsenic-containing liquid. The temperature of the arsenic-containing liquid is preferably 10 to 30 °C. The number of bacteria in the arsenic-containing liquid is preferably 10 2 ~10 9 cells / ml, more preferably 104 ~10 7 cells / ml.

[0027] (Reaction process) In the reaction process, iron-oxidizing bacteria having the ability to oxidize ferrous ions to ferric ions and the ability to oxidize arsenous acid to arsenic acid (or, when a mixture of bacteria is used, iron-oxidizing bacteria having the ability to oxidize ferrous ions to ferric ions) are brought into contact with ferrous ions, whereby iron(III) hydroxide minerals are formed. Note that, as described in the examples below, this iron(III) hydroxide mineral contains a large amount of ferrihydrite having a large positive charge and a large surface area, which can function as an adsorption medium for adsorbing various anions (e.g., arsenous acid and arsenic acid). That is, arsenous acid and arsenic acid present in the arsenic-containing liquid can be adsorbed onto the iron(III) hydroxide mineral.

[0028] This reaction process can proceed with the reaction in a state of being left standing in a normal room. Specifically, ferrous ions and arsenous acid gather on the surface of the iron-oxidizing bacteria just by leaving them standing, and iron(III) hydroxide minerals are formed by this iron-oxidizing bacteria and ferrous ions. Thereafter, arsenic (arsenous acid and arsenic acid) is adsorbed onto this iron(III) hydroxide mineral, and after arsenous acid is oxidized to arsenic acid by the iron-oxidizing bacteria, the iron(III) hydroxide mineral adsorbed with arsenic acid can be precipitated. Although the reaction can proceed in a state of being left standing, the reaction can also be advanced by stirring by a known stirring method as appropriate. The standing period is appropriately determined according to the concentration of arsenic contained in the arsenic-containing liquid. For example, in the case of a relatively high arsenic concentration (75 ppm = 1 mM), considering the elapsed time in FIG. 8 described below, it is preferably at least about 5 days, more preferably at least about 6 days. The standing temperature of the arsenic-containing liquid is preferably about 10 to 30°C.

[0029] (Separation process) In the separation process, the iron(III) hydroxide mineral adsorbed with arsenous acid and arsenic acid is separated from the arsenic-containing liquid.

[0030] Examples of separation methods include known separation methods (for example, known filtration methods, known decantation methods, and centrifugation methods).

[0031] [Others] (Culture method) The culture of the iron-oxidizing bacteria of the present invention can be carried out by the culture method described in "<Culture of Roseovarius sp. OM2 strain, gene analysis derived from bacteria, isolation confirmation, and phylogenetic analysis>" in the following examples and the common general knowledge of those skilled in the art.

[0032] The medium preferably contains ammonium chloride, magnesium sulfate, calcium chloride, potassium phosphate, sodium hydrogen carbonate, and Yeast Extract. The culture temperature is preferably 10 to 30 degrees. The culture pH is preferably 5 to 8.

Examples

[0033] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.

[0034] <Culture of Roseovarius sp. OM2 strain, gene analysis derived from bacteria, isolation confirmation, and phylogenetic analysis> To 8 ml of a solution obtained by adding iron sulfide (FeS) as an Fe(II) source and As(III) (final concentration 0.1 to 0.5 mM) as an arsenic source to the basic medium for accumulation shown in Table 1 below (the compositions of the wolfe's mineral solution and Vitamin solution contained in this medium are shown in Tables 2 and 3 below), 100 μl of a dilution of hot spring sediment (sample collection site: hot spring area in Shimane Prefecture), which is a seeding source, was added and cultured by accumulation at 28°C. The dilution solution was a solution serially diluted from 10 2 times to 10 8 times, and 3 to 5 media were prepared at each dilution rate. After 2 to 3 weeks, the medium in which the formation of an iron oxide band was confirmed was collected, and again, 10 2 times to 10 8Serial dilution was performed up to [multiple] times and cultured at 28 °C for another 2 - 3 weeks in a new medium. The formation of the iron oxide band became apparent as shown in Figure 2.

[0035]

Table 1

[0036]

Table 2

[0037]

Table 3

[0038] Next, for the medium in which the formation of the iron oxide band was confirmed, bacterial gene analysis, isolation confirmation, and phylogenetic analysis were performed.

[0039] Analysis of the bacterial arsenic oxidase gene (aioA) was performed by PCR amplicon analysis using oligonucleotide primers specific to the aioA sequence. As a result, as shown in Figure 3, it was revealed that the arsenic oxidase gene was possessed. Also, the possession of aioA was confirmed in the whole genome analysis of strain OM2 by shotgun metagenome analysis.

[0040] Isolation confirmation was performed by denaturing gradient gel electrophoresis targeting the bacterial 16S rRNA gene. As a result, a single band was confirmed as shown in Figure 4, indicating that Fe / As-oxidizing bacteria had been isolated.

[0041] Phylogenetic analysis was carried out using a phylogenetic tree based on the partial nucleotide sequence of 16S rRNA to analyze the phylogenetic position of Roseovarius sp. OM2 strain. For the construction of the phylogenetic tree, the software MEGA11 (https: / / www.megasoftware.net / ) was used. A phylogenetic tree based on the partial nucleotide sequence of 16S rRNA was constructed to analyze the phylogenetic position of Roseovarius sp. OM2 strain. As a result of the phylogenetic analysis, it was revealed that the Roseovarius sp. OM2 strain belongs to the genus Roseovarius as shown in Figure 5. In Figure 5, the scale bar at the lower left is 0.01, indicating 1% of different bases. The numbers located at the branches of the phylogenetic tree indicate bootstrap values.

[0042] Furthermore, through the above phylogenetic analysis, it was found that the Roseovarius sp. OM2 strain is a new species of bacteria closely related to Roseovarius azorensis SSW084 KC534172. The ratios of Digital DNA-DNA Hybridization and Average Nucleotide Identity of the Roseovarius sp. OM2 strain (relative to Roseovarius azorensis SSW084 KC534172) are shown in Table 4 below.

[0043]

Table 4

[0044] As a result of the whole genome analysis of Roseovarius sp. strain OM2 by shotgun metagenome analysis, the nucleotide sequence of the 16S rRNA gene of Roseovarius sp. strain OM2 (SEQ ID NO: 1) was as shown in Table 5 below. This nucleotide sequence is the same as the nucleotide sequence in the column of the "Sequence Listing" described later.

Table 5

[0045] <Confirmation of the oxidation activity of ferrous ions to ferric ions, confirmation of the oxidation activity of arsenite to arsenate, confirmation of the oxidation rate of arsenite to arsenate, and confirmation of the removal efficiency of dissolved arsenic by Roseovarius sp. strain OM2> The samples used in the above confirmation were prepared by the following method.

[0046] (Method for preparing a sample containing Roseovarius sp. strain OM2 in an Fe&As coexistence system) To 8 ml of a solution prepared by adding iron sulfide (FeS) as an Fe(II) source and As(III) (final concentration 1 mM) as an arsenic source to the basic culture medium for experiments shown in Table 5 below, OM2 strain that had been pre-cultured (OM2 strain cultured in "<Culture of Roseovarius sp. strain OM2, gene analysis derived from bacteria, isolation confirmation, and phylogenetic analysis>") was added at an initial cell number of 1×10 6 cells / ml, and then statically cultured at room temperature (25 - 28°C). The culture was carried out for 15 days, and samples of the culture medium (suspension sample containing iron oxide and cells) and the sample obtained by filtering the culture medium through a filter (pore size 0.20 μm) (aqueous solution sample) were collected at 3-day intervals from the start of the culture.

[0047]

Table 6

[0048] (Method for preparing a sample containing Roseovarius sp. strain OM2 in an As system) For 8 ml of the medium obtained by adding As(III) (final concentration: 1 mM) as an arsenic source to the above-described basic medium for experiments, the OM2 strain that had been pre-cultured (the OM2 strain cultured in "<Culture of Roseovarius sp. strain OM2, genetic analysis of bacteria-derived genes, confirmation of isolation, and phylogenetic analysis>") was added at an initial cell number of 1×10 6 cells / ml, and then static culture was performed at room temperature (25 to 28°C). Similarly, culture was performed for 15 days, and samples of the medium (suspension sample containing iron oxide and cells) and the sample obtained by filtering the medium through a filter (pore size: 0.20 μm) (aqueous solution sample) were collected at 3-day intervals from the start date of the culture.

[0049] <Confirmation of the oxidation activity of divalent iron ions of Roseovarius sp. strain OM2 to trivalent iron ions> To confirm the oxidation activity of divalent iron ions of Roseovarius sp. strain OM2 to trivalent iron ions, changes in the cell number in the Fe&As coexistence system and changes in the concentration of trivalent iron ions (Fe(III)) accompanying the changes in the cell number were confirmed. The cell number and the concentration of trivalent iron ions were determined by the methods shown below.

[0050] (Method for determining the cell number) The cell number was counted using a known fluorescence microscope after staining the cells of the OM2 strain contained in the collected suspension sample with a nucleic acid staining agent (such as DAPI or SYTO9).

[0051] (Method for determining the concentration of trivalent iron ions) The concentration of trivalent iron ions was calculated by subtracting the concentration of divalent iron ions from the total iron ion concentration contained in the sample obtained by completely dissolving the collected suspension sample with 3M hydrochloric acid (hereinafter referred to as the total dissolution sample). The total iron ion concentration was quantified using a known ICP emission spectrometer. The concentration of divalent iron ions was measured by the phenanthroline method.

[0052] (Results) The results of the change in the cell count of Roseovarius sp. strain OM2 and the change in the ferric ion concentration accompanying the change in its cell count are shown in Fig. 6. As shown in Fig. 6, it was found that the ferric ion concentration increased with the increase in the cell count over time. That is, it became clear that Roseovarius sp. strain OM2 has the activity (oxidation ability) to oxidize ferrous ions to ferric ions.

[0053] <Confirmation of the oxidation activity of arsenite to arsenate by Roseovarius sp. strain OM2> To confirm the oxidation activity of arsenite (As(III)) to arsenate (As(V)) by strain OM2, the ratio of arsenite to arsenate was confirmed in the case where strain OM2 was inoculated and the case where strain OM2 was not inoculated in the Fe&As coexistence system. The arsenite concentration and the arsenate concentration were determined by the following method.

[0054] (Method for determining the arsenite concentration and the arsenate concentration) The arsenate concentration was calculated by quantifying the total arsenic concentration in the total dissolution sample using an ICP emission spectrometer and then subtracting the arsenite concentration in the total dissolution sample measured by the hydride generation method from the total arsenic concentration. The dissolved arsenic concentration was quantified by measuring the total arsenic concentration in the aqueous solution sample using an ICP emission spectrometer.

[0055] (Results) The results of the ratio of arsenite to arsenate in each case are shown in Fig. 7. As shown in Fig. 7, it was found that when Roseovarius sp. strain OM2 was inoculated, the ratio of the arsenite concentration increased over time compared to the case where it was not inoculated. That is, it became clear that Roseovarius sp. strain OM2 has the oxidation activity of arsenite to arsenate.

[0056] <Confirmation of the oxidation rate of arsenite to arsenate> To confirm the oxidation rate of arsenite (As(III)) to arsenate (As(V)), the ratio of arsenite to arsenate was confirmed in the case of the Fe&As coexistence system and the case of the As single system. The arsenite concentration and the arsenate concentration were determined by the method described above.

[0057] The results regarding the ratio of arsenous acid to arsenic acid in each case are shown in Fig. 8. As shown in Fig. 8, it was found that the oxidation rate to arsenic acid is higher in the presence of Fe. That is, it became clear that the case of the Fe&As coexistence system is more preferable for the arsenic removal method.

[0058] <Confirmation of Dissolved Arsenic Removal Efficiency> To confirm the dissolved arsenic removal efficiency, the removal rates of dissolved arsenic (arsenous acid and arsenic acid) in the case of the Fe&As coexistence system and the case of the As single system were confirmed. This removal rate was determined by the following method.

[0059] (Method for Determining the Removal Rates of Arsenous Acid and Arsenic Acid) Samples (aqueous solution samples) obtained by filtering the medium through a filter (pore size 0.20 μm) were collected over time, and the arsenic concentration in the samples was quantified using an ICP emission spectrometer. The removal rate was calculated by dividing the quantified arsenic concentration by the initial arsenic concentration (1 mM).

[0060] The results regarding the removal rate of dissolved arsenic are shown in Fig. 9. As shown in Fig. 9, it became clear that dissolved arsenic acid is efficiently removed in the Fe&As coexistence system.

[0061] <Identification of Iron Oxide Minerals Produced by Roseovarius sp. Strain OM2> The (suspended) sample collected in the above-mentioned “(Method for Preparing a Sample Containing Roseovarius sp. Strain OM2 in the Fe&As Coexistence System)” was filtered through a filter (pore size 0.20 μm), and the precipitate remaining on the filter was dried and used as a sample for identifying iron oxide minerals. The Fe K-edge X-ray absorption fine structure (XAFS) spectrum of the dried sample was obtained, and this obtained spectrum was compared with the spectra of iron oxide mineral standard samples (ferrihydrite, goethite, lepidocrocite). By this comparison, the iron oxide minerals produced by strain OM2 were identified.

[0062] The XAFS analysis was carried out at the synchrotron radiation facility KEK-PF BL12C (Tsukuba City). The results of this XAFS analysis are shown in Fig. 10. Spectral fitting was performed using the standard sample spectrum, and based on this, the content ratio (%) of the contained iron oxide minerals was calculated. The results are shown in Table 6 below.

[0063]

Table 7

[0064] As is clear from the above table, the iron oxide mineral contained the most ferrihydrite.

[0065] <Confirmation of elemental maps in Roseovarius sp. OM2 strain by SEM> The (suspended) sample collected in the above-mentioned “(Method for preparing a sample containing Roseovarius sp. OM2 strain in an Fe&As coexistence system)” was observed with a known scanning electron microscope (SEM) to confirm the elemental map in the Roseovarius sp. OM2 strain. The results are shown in Fig. 11.

[0066] By comparing the left photo with the middle photo, it was confirmed that iron (Fe) was formed at the location where the Roseovarius sp. OM2 strain exists. By comparing the middle photo with the right photo, it was confirmed that arsenic (As) was adsorbed at the location of the formed iron.

Claims

1. An iron-oxidizing bacterium characterized by having the ability to oxidize ferrous ions to ferric ions and the ability to oxidize arsenous acid to arsenic acid.

2. The iron-oxidizing bacterium according to claim 1, wherein the iron-oxidizing bacterium belongs to the genus Roseovarius.

3. The iron-oxidizing bacterium according to claim 2, wherein the Digital DNA-DNA Hybridization of the iron-oxidizing bacterium with Roseovarius azorensis is 15 to 45%, and the Average Nucleotide Identity of the iron-oxidizing bacterium is 70 to 90%.

4. The iron-oxidizing bacterium according to claim 2, wherein the iron-oxidizing bacterium is Roseovarius sp. OM2 strain represented by the accession number NITE AP-03992 at the Patent Microorganisms Depositary, National Institute of Technology and Evaluation.

5. A material comprising the iron-oxidizing bacterium according to any one of claims 1 to 4 and a support material on which the iron-oxidizing bacterium can live.

6. An addition step of adding an iron-oxidizing bacterium having the ability to oxidize ferrous ions to ferric ions and the ability to oxidize arsenous acid to arsenic acid according to any one of claims 1 to 4, or a mixture of an iron-oxidizing bacterium having the ability to oxidize ferrous ions to ferric ions and a bacterium having the ability to oxidize arsenous acid to arsenic acid into an arsenic-containing liquid, a reaction step including that an iron-oxidizing bacterium having the ability to oxidize ferrous ions to ferric ions and the ability to oxidize arsenous acid to arsenic acid or a bacterium having the ability to oxidize ferrous ions to ferric ions contacts with ferrous ions to form a ferric hydroxide (III) mineral capable of adsorbing arsenous acid and arsenic acid, and arsenous acid is adsorbed on the ferric hydroxide (III) mineral, and the iron-oxidizing bacterium having the ability to oxidize ferrous ions to ferric ions and the ability to oxidize arsenous acid to arsenic acid or the bacterium having the ability to oxidize arsenous acid to arsenic acid oxidizes arsenous acid to arsenic acid, and a separation step of separating the ferric hydroxide (III) mineral adsorbed with arsenous acid and / or arsenic acid from the arsenic-containing liquid, characterized by including the above steps, a method for removing arsenic in an arsenic-containing liquid.

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