Isolation, Identification And Fe(Ⅲ) Reducing Characteristics Of Fe(Ⅲ)/Humus-reducing Bacteria

Iron/humus respiration is the oldest respiration form in the earth, which generally existsin soil, sediment and stratum and plays a key role in ecology environments:including the bio-geochemical cycle of major elements and the transformation process of organic contaminants. As a hot topic internationally, the characterization of iron/humus respiration, as well as the exploration of the iron/humus-reducing bacteria, has been studied widely. Inthis work, numbers of iron/humus-reducing microbes were isolated from several samples (the paddy soil and humus-rich sludge collected from different areas) using the classical method of enrichment under the anaerobic conditions. After that, the iron/humus-reducing bacteria that represents novel species were selected as targets, of which the iron and humus reduction features with different electron acceptors and donors were studied. The main conclusions were described as follows:1. A total of58bacteria capable of reducing iron or humus were isolated, purified and identified. Among these isolates, most were Gram-negative and mainly classified to be genera Citrobacter and Pseudomonas,2bacteria belonged to genus Bacillus and only one was actinomycetes.2. On basis of physiological and biochemical characters, phylogenetic analysis and DNA-DNA hybridization, there were four iron/humus-reducing bacteria that identified as representatives of novel species i.e. Rhodobacter ferrireducens SgZ-3T, Bacillus composti SgZ-9T, Bacillus thermophilus SgZ-10T and Bacillus humiphilum GD03T.3. In the investigation of humus-reducing characters of above four novel bacteria, all strains showed the strongest reduction capacity with glucose as the electron donor, which well indicated that the electron donor structure and solubility had a marked impact on humus-reducing. The effects of different electron acceptors on iron-reduction were studied, and the results revealed that the four types of Fe(Ⅲ)(hydr)oxides can be reduced by all of the four strains with glucose as electron donor; and the reduction rateratio of ferrihydrite was the highest, followed by lepidocrocite, goethite and hematite, which suggested that the Fe(Ⅲ)-oxides with poor crystallinity was relatively reduced easily. With different electron donors, the Fe(Ⅲ)-reducing ability of strains SgZ-3T varied, and the electron donor with high solubility generally bring high reduction rateratio of Fe(Ⅲ)-oxides.