The Isolation, Characterization And Iron Oxides Reducing Test Of A Dissimilatory Fe(Ⅲ)-and Nitrate-reducing Bacterium

Ferric-reducing bacteria, as one of the most important reducing bacteria, werewidely distributed in soil, lakes, swamps, and marine depositional environment.Under reducing anaerobic environment, these microorganisms are able to use notonly Fe （Ⅲ） as the terminal electron but also a variety of other electron donors andacceptors to sustain cell growth. Their metabolic processes and their interactionswith the iron-bearing minerals are coupled with the cycle of C, N, P, S and someother heavy metal elements in the Earth’s ecosystem, which has importantenvironmental significance. Strengthen these microbial groups in the reduction offlux will help to solve environmental problems. In order to study ferric-reducingbacteria in detail, we have isolated strains from a copper mine tailings, explored thephysiological and biochemical characterization and molecular biologicalidentification of the isolate, optimized its growth condition, and investigated itsgrowth process, surface properties, flocculation performance and inducedbiomineralization. The obtained main results are as follows:（1） A facultative anaerobic dissimilatory Fe（Ⅲ）-and nitrate-reducingbacterium was isolated from the Linchong tailings, a skarn-type copper minetailings in China. The isolate, designated as strain CW, was a gram-negative androd bacterium.16S rRNA gene, phenotypic and biochemical analysis placed strainCW in the Gramma subgroup of the proteobacteria and finally incorporated intoPseudomonas stutzeri （CCTCC AB2013114）. It was able to grow at temperaturesof30⁴0°C and pH of7.0⁸.0.（2） Through the research on substrate metabolism process it was found that thebacteria can respectively reduce Fe（Ⅲ） and nitrate to Fe（Ⅱ） and nitrogen gas underanaerobic conditions. XRD analysis of metabolic solid product showed that thevivianite was formed from Fe（Ⅱ） produced and the phosphate compound in themedium. When nitrate and Fe （Ⅲ） coexisted, strain CW can reduce two electronacceptors simultaneously. It was the first time to report a Pseudomonas sp. isolatedfrom anaerobic zone of skarn copper tailings which can reduce both nitrate and Fe（Ⅲ）.（3） The three-level orthogonal experiment with the two factors of temperatureand pH value was conducted and optimized conditions for cell growth ofPseudomonas stutzeri CW and the production of nitrogen was35°C, pH7and35°C, pH8, respectively. When carbon source was sufficient with nitrate assubstrate, the kinetics of nitrate reduction, microbial growth and nitrogengeneration process was investigated under the optimized conditions for nitrogenproduction.（4） The relationship between cells dry weight and culture OD600was: Cell dryweight （mg/L）=533.14×OD₆₀₀－6.48（R²=0.99）. Through a preliminary studyabout the cell surface component and flocculation ability, we found that the cellsurface binding extracellular polymeric substances have good flocculation effect.（5） Experiments were carried out to study the effects of DIRB and SRB on thedecompositions of magnetic iron oxides, namely magnetite and maghemite. It wasfound that in experiment without sulfate, the magnetism of the experimental systemwas promoted with the mediation of SRB, and besides some vivianite wasprecipitated. In experiment with sulfate, sulfate was reduced to H2S by SRB, andthe produced H2S subsequently reacted with iron oxides and leaded to the formationof iron sulfides. As a result, magnetism of this experimental system droppedsharply. In experiment with sulfate and both DIRB and SRB inoculated, similarresults were achieved as that of experiment with only SRB inoculated.