| Ocean has existed for more than four billion years on the earth, encompasses 70% the earth's surface, which contains rich resources. As a model pattern of redox process, deep sea sediment has an important role in studying deep-sea ecology environment. Fe(Ⅲ)-Reducing is an significant process of which, major occurring in anaerobic environment(such as marine sediment,fresh water sediment and flooding paddy soil), is a microbial metabolism taking Fe(Ⅲ) as terminal electron acceptor. Therefor, study of Fe(Ⅲ) reduction characteristics is benefit to illustrate the reducing mechanism of iron reducers and to understand the important role of iron reduction in marine ecology environment, which has an important theory and practice meaning on improving pollutant transformation and bioremediation.The microbial diversity of Fe(Ⅲ)-reducing enrichments from different samples was analyzed. One sample was hydrothermal sulfide, which was from Southeast Pacific Ocean; other samples were from Southwest Pacific Ocean. The cultures were enriched using sodium lactate as electron donor and ferric hydroxide as electron accepter. The result of 16S rDNA gene clone library of enrichment from Southeast Pacific Ocean showed that clones were clustered into two groups, Proteobacteria was the dominant group, compared to total bacterial clones, could reach 72.4%, which were mainly distributed in 3 subgroups:ε- (55.2%),β- (10.3%) andα-(6.9%) Proteobacteria. Another bacterial group was Firmicutes (27.6%). The BLASTn analysis of the sequences and phylogenetic tree showed that the functional strains in the enrichments to reduce ferric hydroxide were mainlyε- proteobacteria which also could reduce S0. Whereas the Fe(Ⅲ)-reducing bacteria from Southwest Pacific Ocean were almost Firmicutes. The results indicate that the main groups of Fe(Ⅲ)-reducing bacteria are different in various marine environments.Three pure strains were isolated from enrichments, which had the highest similarities of Clostridium halophilum (94.972%),Tepidibacter formicigenes(95.055%)and Citrobacter freundii(98.696%). At last , the isolate DY192 from southwest Pacific Ocean (W 175.9562°, S 19.7418°,2350m) was classified and described as a novel type strain named Clostridium ferrireducens. Strain DY192~T was straight to slightly curved rods, 1.0-1.2μm in diameter and 6.0-8.0μm in length. The cells occurred singly or in pairs, and had a few laterally inserted flagella. Growth was observed only under strictly anaerobic conditions,over a temperature range of 10 to 45°C with an optimum at 40°C. Under optimal conditions,the generation time was about 34 minutes. The pH and salinity range were 6.5-8.5 (optimum 8.0) and 0.5%-8.5% NaCl (optimum 4.0-5.0%),respectively. Strain DY192 is a heterotrophic organism growing on complex carbon sources such as peptone,tryptone,yeast extract and beef extract. Analysis of the 16S rDNA sequence (1438 bp,HQ696463) indicated that strain DY192 is a member of the genus Clostridium,most closely related to Clostridium halophilum. The G+C content of the genomic DNA of strain DY192 was 32.5 mol%.This paper described the diversity of Fe(Ⅲ)-reducing bacteria from different samples of Southeast Pacific Ocean and Southwest Pacific Ocean, provided for the first time an insight into it,especially Fe(Ⅲ)-reducing bacteria participated in Iron metabolism.
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