A Survey For Cr-resistant And/or-reducing Bacterial Taxa

In this study, an investigation of Cr-resistant and/or-reducing bacterial taxa was carried out using genome mining, culture-dependent method and literature survey to provide pivotal bacteria for Cr pollution renovation.(1) The diversity of Cr(VI)-resistant bacteria. For investigating the diversity of Cr(VI)-resistant strains, chrA was selected for in silico genome mining from JGI genome database. In silico genome mining revealed that 1877 species of 7887 (23.8%) investigated bacterial species contained Cr-resistant gene chrA. These bacteria were distributed in 21 phyla including Proteobacteria (1091 species), Firmicutes (237 species) and Bacteroidetes (181 species), etc. Genera Pseudomonas (49 species), Bacillus (46 species) and Vibrio (43 species) were the three most abundant genera. By culture-dependent method,9 Cr(VI)-resistant strains were isolated from xixi wetland sediment, including four Actinobacteria, three Proteobacteria and two Firmicutes. Among these, Lactococcus sp. GL02 represent a novel Cr(VI)-resistant genus. Additonaly, a novel strain S31T isolated from xixi wetland sediment showed weak resistant capacity to Cr(VI) which could tolerate up to 10 mg·L-1’K2Cr2O7. Based on its phenotypic and chemotaxonomic characteristics and phylogenetic data, strain S31T represents a novel species of the genus Epilithonimonas, for which the name Epilithonimonas xixisoli sp. nov. is proposed.(2) The diversity of Cr(VI)-reducing bacteria. For investigating the diversity of Cr(VI)-reducing strains, Cr(VI) reductase gene was selected for in silico genome mining from JGI genome database.81 speceis of 7887 species (1.1%) were found containing Cr(VI) reductase genes. These bacteria belonged to Proteobacteria (51 species), Firmicutes (23 species), Actinobacteria (6 species) and Bacteroidetes (1 species). Bifidobacterium (5 species), Bordetella (5 species) and Bacillus (5 species) were the most abundant genera.(3) The diversity of Cr(VI)-resistant and-reducing strains. In JGI genome database,36 species containing both chrA and Cr(VI) reductase genes were identified. They were distributed in 3 phyla and 30 genera, with Bordetella (4 species) being the most abundant genus. To get a full census of Cr(VI)-resistant and-reducing genera, a thorough survey on published literatures conmbined with our in silico genome mining results were analysed for Cr(VI)-resistant and-reducing genera diversity. In summary, there were 69 genera which affiliated to 5 phyla,9 classes,27 orders and 46 families. The phylum Proteobacteria was the most abundant (39 genera). Among the 9 Cr(VI)-resistant strains isolated from xixi wetland sediment, only one strain Arthrobacter sp. GL06 was also able to reduce Cr(VI).In this study, we presented the most comprehensive taxa of Cr(VI)-resistant and/or reducing bacteria so far by combined culture-dependent and in silico genome mining. Both methods indicated that bacteria belonged to Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria had the greatest potential in bioremediation. Some important groups of Cr(VI)-resistant and/or-reducing bacteria were also identified, such as genus Pseudomonas, Bacillus, Vibrio, Bifidobacterium, Bordetella, Arthrobacter and Lactococcus, etc. These bacteria may play important roles in bioremediation. Based on Our investigation, there are still some novel Cr(VI)-resistant and/or-reducing bacteria needed to be identified.