JP5150282B2 - Novel photosynthetic bacterial strain having high heavy metal adsorption ability and environmental purification method using such bacterial strain - Google Patents

Description

  The present invention relates to a photosynthetic bacterial strain exhibiting a high adsorption capacity for a wide range of heavy metals including radionuclides. The present invention also relates to an environmental purification method using such a bacterial strain.

  In recent years, heavy metal contamination such as sludge and soil due to factory effluent and nuclear tests has become a problem in various parts of the world. As countermeasures against this, it is conventionally known to recover heavy metals from sludge and soil using photosynthetic bacteria having the property of adsorbing heavy metals. For example, Patent Document 1 discloses that a surface-modified porous ceramic in which a magnetic substance and photosynthetic bacteria are immobilized on a porous ceramic is dispersed in sludge so that heavy metals in the sludge are adsorbed to the photosynthetic bacteria. A method for recovering the fixed ceramic together with the magnet from the sludge is disclosed.

  In the method of Patent Document 1, as a photosynthetic bacterium used for adsorbing common heavy metals such as Cu, Ag, and Hg, Rhodobacter sphaeroides S strain, Rhodobulum sp PS88 strain, Rhodopus eudomonas pulse thuris (Rhodopseudomonas palustris), Rhodobacter capsulata and the like. Although these photosynthetic bacteria are known to have a certain heavy metal adsorption capacity, they are still insufficient in capacity to recover heavy metals.

In addition to the recovery of heavy metals of the kind described above, there is a strong demand for effective recovery of radionuclides such as Sr, U, and Co from the environment in order to deal with nuclear contamination caused by nuclear facilities and nuclear tests. It has been. Therefore, there is a need for a photosynthetic bacterial strain that can effectively adsorb a wide range of heavy metals including radionuclides.
Japanese Patent Laid-Open No. 2001-25786

  The present invention was devised in view of the current state of the prior art, and the object thereof is a photosynthetic bacterial strain exhibiting a high adsorption capacity for a wide range of heavy metals including radionuclides, and an environment using such a bacterial strain. It is to provide a purification method.

  The present inventors are a biotechnology of Rhodobacter sphaeroides S strain (deposit number: NBRC100038 (NITE (National Institute for Product Evaluation Technology)), which is known to have a relatively high heavy metal adsorption capability among photosynthetic bacterial strains. Field Deposited in the Department of Biological and Genetic Resources)) We found a natural mutant that showed the property that cells gather (aggregate) during subculture. Therefore, the present inventors isolated this natural mutant and investigated further, and found that the aggregation of this natural mutant was brought about by the production of a large amount of cell surface proteins and RNA, and that these proteins and RNA were The present inventors have found that heavy metals can be strongly and electrically adsorbed by use, and have completed the present invention.

  That is, according to the present invention, the Rhodobacter sphaeroides SSI strain (FERM) having the ability to adsorb heavy metals (for example, common heavy metals such as Cu, Ag and Hg and heavy metals belonging to radionuclides such as Sr, U and Co). P-21462) is provided. According to the present invention, there is also provided a method for purifying an environment contaminated with heavy metals as described above (for example, sludge, sediment sand, soil, desert sand, etc.), comprising the Rhodobacter sphaeroides SSI strain ( FERM P-21462) adsorbs heavy metals in the environment, and a bacterial strain adsorbed with the heavy metals is recovered from the environment.

  Since the bacterial strain of the present invention produces a large amount of cell surface proteins and RNA, it exhibits a high heavy metal adsorption ability. In particular, the bacterial strain of the present invention exhibits high adsorption ability not only for common heavy metals such as Cu, Ag, and Hg but also for radionuclides such as Sr, U, and Co. Therefore, the use of the bacterial strain of the present invention can effectively purify not only the environment contaminated with heavy metals such as factory wastewater but also the environment contaminated with radionuclides by nuclear facilities and nuclear tests.

  Hereinafter, the bacterial strain of the present invention will be described first, and then the environmental purification method using this bacterial strain will be described.

  Rhodobacter sphaeroides SSI strain (hereinafter simply referred to as SSI strain), which is a bacterial strain of the present invention, is obtained during subculture of the photosynthetic bacterium Rhodobacter sphaeroides S strain (hereinafter simply referred to as S strain). It is a natural mutant obtained. The SSI strain of the present invention is deposited at the Patent Organism Depositary, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi 1-1-1, Tsukuba, Ibaraki Prefecture, and can be easily obtained from there. The accession number of the SSI strain of the present invention is FERM P-21462 (consigned on December 7, 2007).

  Conventional photosynthetic bacterial strains, including the parent strain S, do not show any aggregation properties, but the SSI strain of the present invention produces a large amount of cell surface proteins and RNA during culture. As a result, bacterial cells aggregate. Due to the presence of these proteins and RNA, the SSI strain of the present invention has a significantly higher heavy metal adsorption capacity than conventional photosynthetic bacterial strains because it electrically adsorbs heavy metals. Therefore, the SSI strain of the present invention can also effectively adsorb heavy metals that are difficult to adsorb as compared to conventional photosynthetic bacterial strains. The bacteriological properties of the SSI strain of the present invention are exactly the same as the parent S strain, except that it exhibits agglutination due to the production of large amounts of cell surface proteins and RNA.

  The SSI strain of the present invention effectively adsorbs any kind of heavy metal ionized in an aqueous solution, for example, common heavy metals such as Cu, Ag, Hg, and Sr, U, Co, etc. that are considered difficult to adsorb. It is possible to adsorb heavy metals belonging to these radionuclides.

  The SSI strain of the present invention can be grown under any culture conditions as long as the strain can effectively grow. For example, the medium described in Table 1 of the Examples (glutamate-malate medium) is used at 30 ° C. It can be easily carried out by culturing at a temperature of ˜35 ° C. under aerobic dark conditions or standing bright conditions (under irradiation with tungsten light of 5 klux to 10 klux).

  The environmental purification method of the present invention is carried out by adsorbing heavy metals in the environment to the SSI strain of the present invention and recovering bacterial strains adsorbed with heavy metals from the environment. The environment that can be purified by the method of the present invention is not particularly limited as long as the SSI strain of the present invention can survive. For example, sediments such as seas, rivers, and lakes, sedimentary sand, ground soil (fields), Can be desert sand.

  In the environmental purification method of the present invention, first, the SSI strain of the present invention is allowed to survive or cultured in an environment contaminated with heavy metals, and the heavy metals in the environment are adsorbed by the bacterial strains. For example, when the environment is sludge or sedimentary sand, the SSI strain of the present invention is added to water on the sludge or sedimentary sand. Moreover, when this environment is ground soil (field) or desert sand, the SSI strain of the present invention is directly added to these soil and sand. At this time, the SSI strain of the present invention is preferably immobilized in advance on a suitable carrier and added together with the carrier. This is to facilitate recovery of the strain after adsorption of heavy metal. Any carrier can be used as long as it has a surface structure capable of immobilizing strains. For example, a porous ceramic carrier is preferable. The porous ceramic carrier preferably contains a magnetic material for easy recovery by a magnet.

  In order for the SSI strain of the present invention to exhibit the ability to adsorb heavy metals, it is necessary to remain alive until the bacterial strain is recovered, and if the bacterial strain dies in the environment, the bacterial strain cells Heavy metals adsorbed on the surface may be released again. Therefore, when it is considered that the nutrient source of the SSI strain of the present invention is insufficient in the environment, it is preferable to add the nutrient source so that the bacterial strain does not die. As this nutrient source, for example, sewage or agricultural drainage can be used. Similarly, when it is considered that temperature conditions, aeration conditions and the like are not suitable conditions for the SSI strain of the present invention, it is preferable to artificially adjust these conditions.

  Heavy metals present in the environment dissolve in water and are in an ionized state, and are positively charged. On the other hand, the SSI strain of the present invention produces a large amount of cell surface proteins and RNA in the environment, and these proteins and RNA are negatively charged. Therefore, the cell surface protein or RNA of the SSI strain of the present invention and heavy metals in the environment are electrically attracted to each other. The method of the present invention uses not only the heavy metal adsorption force of conventional photosynthetic bacteria, but also the electrical attractive force of these surface proteins and RNA. Therefore, according to the method of the present invention, not only contamination of general heavy metals such as Cu, As, and Hg but also contamination of radionuclides such as Sr, U, and Co, which have been conventionally considered difficult to adsorb. Can also deal with.

  In the environmental purification method of the present invention, after the heavy metal in the environment is adsorbed to the SSI strain of the present invention, the bacterial strain adsorbed with the heavy metal is recovered from the environment. The recovery method is not particularly limited. For example, when the SSI strain of the present invention is immobilized on a carrier, the carrier is sucked to easily recover the SSI strain of the present invention together with the carrier from the environment. can do. When the carrier is not used, the SSI strain of the present invention can be recovered from the environment by sucking and separating the liquid in which the SSI strain of the present invention survives with a pump.

  The SSI strain of the present invention can be recovered from the environment at a time when the SSI strain of the present invention seems to have sufficiently adsorbed heavy metals. The collection time varies depending on the concentration of the bacterial strain, the type of heavy metal, and the culture conditions, but is generally about 3 days to about 1 week after the addition of the bacterial strain.

  Since the microbial cells recovered from the environment adsorb heavy metals, the heavy metals can be separated from the microbial cells if necessary. However, if separation of heavy metals is not necessary, they may be incinerated as they are. When separating heavy metals, the separation can be easily performed by acid washing of the collected cells.

  Hereinafter, the high heavy metal adsorption ability of the SSI strain of the present invention will be specifically demonstrated by Examples. In addition, description of an Example is given only for an understanding of invention, and this invention is not limited at all by this.

Bacterial strain used Rhodobacter sphaeroides SSI strain (hereinafter simply referred to as SSI strain) was used as the bacterial strain of the present invention example. Further, as bacterial strains of comparative examples, Rhodobacter sphaeroides S strain (hereinafter simply referred to as S strain), Rhodobacter sphaeroides IFO12203 strain (hereinafter simply referred to as IFO12203 strain), and Rhodopus eudomonas pulse thuris ( Three bacterial strains (hereinafter simply referred to as R. palustris) were used. Of the three bacterial strains of the comparative examples, the S strain is the parent strain of the SSI strain of the present invention example, the IFO 12203 strain is a photosynthetic bacterial strain belonging to the same species as the SSI strain of the present invention example, and R . palustris is a photosynthetic bacterium belonging to a different species from the SSI strain of the present invention example.

Investigated heavy metals In this example, the adsorption capacity for six kinds of heavy metals, Sr, U, Co, Cu, As and Hg, was investigated. Among these, Sr, U and Co are heavy metals belonging to radionuclides, and Cu, As and Hg are general heavy metals.

Growth of Bacterial Strains and Immobilization of Bacteria Each bacterial strain was allowed to grow by standing culture for 4 days under irradiation of tungsten light at 30 ° C. and 10 klux in a culture solution having the composition shown in Table 1 below.

After growth, the cells of each bacterial strain were collected by centrifugation, the concentration was adjusted to OD ₆₆₀ ≈50 (25 g / l), and an equal amount of 3.6% by weight sodium alginate was added thereto. To prepare a mixed solution. This mixed solution was immersed in a porous ceramic carrier (manufactured by Nagao Co., Ltd., porosity 80%, pore diameter about 1 mm). After the mixed solution has sufficiently penetrated into the pores in the porous ceramic carrier, the porous ceramic carrier is immersed in a 1.8 wt% calcium chloride solution to exchange sodium ions and calcium ions, and then dried at room temperature. Thus, a porous ceramic carrier (hereinafter referred to as a bacterial cell-immobilized carrier) in which the bacterial cells were immobilized on the pores in the carrier and on the surface of the carrier was obtained.

Preparation of artificial sewage Artificial sewage having the composition shown in Table 2 below was prepared as a nutrient source for bacterial strains in a heavy metal-contaminated environment.

Example 1. Examination of Sr adsorption capacity of the bacterial strain of the present invention Sr was added in the form of nitrate to the artificial sewage prepared as described above to prepare a culture solution in which Sr was dissolved. Placed in a 5 l plastic container with a lid. At this time, the initial concentration of Sr as an element was adjusted to 20 mg / l.

  In this culture solution, prepare a cell in which the bacterial cell immobilization carrier of each bacterial strain is put, a cell in which the cell has not been immobilized, and a cell in which neither the cell nor the carrier is added. Aerobic dark culture was performed for 6 days. The culture conditions were controlled so that aeration was 1 vvm, pH was 6.5 to 7.5, and temperature was about 30 ° C. During the culture, the sample solution was collected on the first day, the second day, the fourth day, and the sixth day, and the concentration of Sr in the sample solution was measured by ICP (radio frequency inductively coupled plasma) emission spectrometry. Each experiment was performed in triplicate with 4 or 8 carriers in the culture solution, and the average of the three measurements was taken as the Sr concentration in the culture solution at each time point. The results when the experiment was conducted with 4 and 8 carriers were shown in FIGS. 1 and 2, respectively.

  As is clear from FIG. 1 and FIG. The Sr concentration in the culture broth was significantly lower than that of the system using palustris, indicating that the SSI strain of the present invention example has a significantly higher Sr adsorption capacity than the conventionally known bacterial strain. Further, the comparison between FIG. 1 and FIG. 2 shows that Sr is better adsorbed as the amount of cells used is larger.

Example 2 Examination of U and Co adsorption ability of the bacterial strain of the present invention U or Co was used instead of Sr as a heavy metal, and R. as a bacterial strain of a comparative example. The experiment was performed in the same manner as in Example 1 except that only palristris was used. U was added to artificial sewage in the form of uranium acetate, not in the form of nitrate. The experiment was carried out with 8 carriers. The results are shown in FIG. 3 for U and in FIG. 4 for Co.

  As is clear from FIG. 3 and FIG. 4, in the system using the SSI strain of the present invention, R.I. The concentration of U or Co in the culture solution was significantly lower than that of the system using Palristris, indicating that the SSI strain of the present invention example has a significantly higher U and Co adsorption capacity than conventionally known bacterial strains. In addition, although a considerable concentration decrease is observed in the control for U, it is thought that this is because U is partially oxidized and becomes a precipitate as time passes, and the ICP method cannot measure the concentration.

  From the results of Examples 1 and 2 above, it is clear that the SSI strain of the present invention has a high adsorption capacity for heavy metals of radionuclides of Sr, U and Co.

Example 3 Examination of adsorption ability of Cu, As and Hg of bacterial strain of the present invention Examples 1 and 2 revealed that the SSI strain of the present invention has a high adsorption capacity for radionuclides. Whether or not the SSI strain of the present invention has a high adsorption capacity even for heavy metals was investigated. Specifically, the experiment was performed in the same manner as in Example 1 except that Cu, As, or Hg was used as the heavy metal instead of Sr. The experiment was carried out with the number of carriers being 2 for Cu and As and 8 for Hg. Moreover, the bacterial strain of the comparative example was not used. The experimental results for Cu, As, and Hg are shown in FIGS.

  As is apparent from FIGS. 5 to 7, the SSI strain of the present invention has a significantly high adsorption capacity for any of Cu, As, and Hg. From the above results, it is clear that the SSI strain of the present invention has a high adsorption ability not only for radionuclides but also for other common heavy metals.

  The novel bacterial strain Rhodobacter sphaeroides SSI of the present invention has a significantly higher adsorption capacity than various conventionally known photosynthetic bacteria for various heavy metals including radionuclides. Therefore, the novel bacterial strain of the present invention can be used extremely effectively to purify environments contaminated with radionuclides such as nuclear facilities and nuclear tests and environments contaminated with heavy metals in factory wastewater.

The change in the Sr concentration in the culture solution when 4 cell-immobilized carriers are introduced is shown. The change in Sr concentration in the culture solution when 8 cell-immobilized carriers are introduced is shown. The change in U concentration in the culture solution when 8 cell-immobilized carriers are introduced is shown. The change in Co concentration in the culture solution when 8 cell-immobilized carriers are introduced is shown. The change in Cu concentration in the culture solution when 2 cell-immobilized carriers are introduced is shown. The change in As concentration in the culture medium when 2 cell-immobilized carriers are introduced is shown. The change in Hg concentration in the culture solution when 8 cell-immobilized carriers are added is shown.

Claims (5)

  Rhodobacter sphaeroides SSI strain (FERM P-21462) with heavy metal adsorption capacity.   The Rhodobacter sphaeroides SSI strain (FERM P-21462) according to claim 1, wherein the heavy metal is a radionuclide.   A method for purifying an environment contaminated with heavy metals, comprising adsorbing heavy metals in the environment by adsorbing heavy metals in the Rhodobacter sphaeroides SSI strain (FERM P-21462) according to claim 1 or 2, Recovering from the environment.   4. The method of claim 3, wherein the environment is sludge, sediment sand, soil, or desert sand.   The method according to claim 3 or 4, wherein the heavy metal is a radionuclide.

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