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Strain-level genomic and physiological variation in four Microbacterium spp.chromate reducers
Henson, M. W., D. R. Learman, P. Kourtev, AND J. W. Santodomingo. Strain-level genomic and physiological variation in four Microbacterium spp.chromate reducers. Presented at ASM Annual Meeting, Poster 2734, Boston, MA, May 17 - 20, 2014.
Sequencing analysis of Microbacterium spp.chromate reducers was performed to better understand the mechanisms governing Cr(VI) reduction in soils
Hexavalent chromium [Cr(VI)], a soluble carcinogen, has caused widespread contamination of soil and water in many industrial nations. Bacteria have been shown to be an active component in the geochemical cycling of chromium, but the mechanisms governing Cr(VI) reduction are poorly understood. Here, we utilized genome sequencing analysis and physiological characterization of chromium reducing Microbacterium isolates (Cr-K1W, K20, K29, and K32) to elucidate key genes involved in chromate reduction. While the four isolates were nearly identical at the 16S rRNA gene level, analysis of growth and chromium reduction revealed physiological differences among the strains. Specifically, Cr-K29 and K32 had the highest rates of Cr(VI) reduction, occurring mainly in the exponential phase of growth. Cr-K1W and K20 reduced at a lesser rate and reduction occurred mainly during stationary phase of growth. Moreover, there appears to be a positive correlation between reduction and resistance to chromate. Genomes of all four isolates contained 35 specific single copy orthologs. Reciprocal best BLAST hits from the draft genomes returned 2,810 proteins shared among the isolates, with the highest chromate reducers (Cr-K29 and K32) sharing an additional 610 proteins. Gene annotation revealed no previously annotated chromate related proteins although two putative chromate reductases were predicted: a flavoprotein and a NADH FMN reductase. Genomic analysis of predictive coding genes and putative chromate reductases suggests potential variation between genomes of high and low chromate reducers. In this study, we provided an examination of strain-level variation in chromate reduction and resistance among aerobic environmental isolates. Further, this study illustrates the lack of known chromate reducatses and the need for greater research into the mechanisms governing chromate cycling in the environment.