Process for the production of hydrogen using photosynthetic prot

Chemistry: molecular biology and microbiology – Micro-organism – tissue cell culture or enzyme using process... – Using bacteria

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75392, 423510, 423DIG17, 435262, 4352625, 4352521, B09B 300, C12P 104

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058044248

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to microbiological methods of heavy-metal oxide or oxyanion removal from aqueous media by Rhodobacter sphaeroides. Several subgenera of Rhodobacter and related species efficiently reduce the metal oxides and oxyanions of selenium, tellurium, europium and rhodium to the free metal which is readily isolated from the cytoplasmic membrane. These microorganisms exhibit resistance to a wide variety of oxides and oxyanions making bioremediation of selected heavy-metal oxides and oxyanions feasible, even in the presence of other oxides and/or oxyanions including those of vanadium, iodine, silicon, molybdenum, tin, tungsten, lead, reuthenium, antimony and arsenic.
2. Description of Related Art
A major environmental problem exists in dealing with toxic metal compounds found ubiquitously dispersed in groundwater, lakes, plant effluents, and aqueous waste. Generally these toxic compounds are heavy metal oxides or oxyanions exemplified by the tellurite, arsenate and periodate classes of oxyanions and oxides. A particularly obnoxious group of contaminants identified as a threat to western United States water supplies includes the oxyanions of selenium frequently found in agricultural wastewaters (Sylvester, 1988).
Potential and actual health problems also arise due to toxic effects of many oxidized heavy metals. Exposure to tellurium compounds is hazardous to workers in the film and rubber industries, as well in battery manufacture. When accumulated in the human body, many of these elements have detrimental mental and physical effects (Schroeder et al., 1967).
Bioremediation has been explored as a method of detoxification of toxic compounds found in water. Proposed methods generally take advantage of microbiological resistance to such compounds. The basis of resistance may be metabolic breakdown or concentration of the material within the microorganism. It is known, for example, that some species of Gram-positive bacteria, such as Corynebacterium diphtheriae, Streptococcus faecalis and most strains of Staphylococcus aureus are naturally resistant to tellurite and will often concentrate metallic tellurium inside the inner membrane (Walter and Taylor, 1989). Resistance determinants to tellurite have been identified and isolated in Escherichia coli (Walter and Taylor, 1989). However, resistance to tellurite is not a common property of bacteria and examples of naturally-occurring resistant strains are rare (Chiong et al., 1988). Oftentimes such resistance is to only low or moderate levels of these compounds, e.g. .ltoreq.100 .mu.g/ml.
A method for accelerating recovery of selenium from aqueous streams is based on bioreduction of Se(VI) to Se(IV) with strains of the soil bacterium, Clostridium. A rapid exchange reaction between selenous acid and pyrite is used to remove the selenium from solution. However, to remove selenium, further processing is required, e.g., generation of hydrogen selenide and subsequent oxidization to the free metal (Khalafalla, 1990). Clostridium species have also been utilized in a process for reducing waste-containing radionuclides or toxic metals, but the process requires obligate anaerobic conditions at elevated temperatures (Francis and Gillow, 1991).
In addition to bioremediation, microorganisms are thought to have practical value in possible reclamation of metals from such sources as low grade ores, or in recovery processing. However, while a few bacterial species have resistance to one or more metal cations under some conditions, resistance may be based on accumulation rather than a metabolic reaction. Few microorganisms have been identified that reduce metal cations to the free metal (Summers and Silver, 1978). Moreover, resistance may not be to whole classes of such compounds, but to only a few.


SUMMARY OF THE INVENTION

The present invention addresses one or more of the foregoing problems in providing a method to effectively bioreduce oxidized metals present in aqueous media. Under certain conditions, some member

REFERENCES:
patent: 4910010 (1990-03-01), Khalafalla
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Chiong et al., "Purification and Biochemical Characterization of Tellurite-Reducing Activities from Thermus thermophilus HB8," J. Bacteriol., 170(7):3269-3273, 1988, published in U.S.A.
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Jobling and Ritchie, "Genetic and physical analysis of plasmid genes expressing inducible resistance of tellurite in Escherichia coli, " Mol. Gen. Gent., 208:288-293, 1987.
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Kiffney and Knight, "The Toxicity and bioaccumulation of Selenate, Selenite and Seleno-L-Methionine in the Cyranobacterium Anabaena flosaquae, " Arch. Environ. Contam. Toxicol., 19:488-494, 1990.
Moore and Kaplan, "Identification and characterization of high-level resistance to tellurite, selenite and other rare-earth oxides in the facultative photoheterotroph, Rhodobacter sphaeroides, " Abstracts of the 91st General Meeting of the American Society for Microbiology, K-128:235, 1991, published in U.S.A.
Rech and Macy, "Location of the Selenate Reducing Activity in a Selenate Respiring Pseudomonas sp.," Abstracts of the 91st General Meeting of the American Society for Microbiology, K-127:235, 1991, published in U.S.A.
Steinberg and Oremland, "Dissimilatory Selenate Reduction Potentials in a Diversity Sediment Types, " Applied and Environmental Microbiology, 56(11):3550-3557, 1990, published in U.S.A.
Summers and Jacoby, "Plasmid-Determined Resistance to Tellurium Compound," J. Bacteriol., 129:276-281, 1977, published in U.S.A.
Summers, "Microbial Transformation of Metals

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