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Metabolic and genomic analysis elucidates strain-level variation in Microbacterium spp. isolated from chromate contaminated sediment
Citation:
Henson, M., J. Santodomingo, P. Kourtev, R. Jensen, J. Dunn, AND D. Learman. Metabolic and genomic analysis elucidates strain-level variation in Microbacterium spp. isolated from chromate contaminated sediment. PeerJ. PeerJ Inc., Corte Madera, CA, , e1395, (2015).
Impact/Purpose:
The objective of this study was to further our understanding of key Cr(VI) reduction mechanisms by examining four chromium reducers isolated from a Cr-rich environment using genomic and biochemical analyses.
Description:
Hexavalent chromium [Cr(VI)], a soluble carcinogen, has caused widespread contamination of soil and water in many industrial nations. Bacteria have been shown to play an active role in the reduction of Cr(VI) to Cr(III), which is insoluble and less toxic, however, the biological mechanisms governing this reaction appear to vary greatly across species. Here, we utilized genome sequencing analysis and physiological characterization of four Cr(VI) reducing Microbacterium isolates (Cr-K1W, Cr-K20, Cr-K29, and Cr-K32) to elucidate key genes involved in chromate reduction. While their 16S gene sequences were nearly identical, growth and chromium reduction analyses revealed physiological differences among the strains. Specifically, Cr-K29 and Cr-K32 had reduced 2 mM of Cr(VI) within 48 hours, while Cr-K1W and Cr-K20 reduced 0.5 and 1.2 mM of Cr(VI) within 120 hours, respectively. Moreover, there appears to be a positive correlation between reduction and resistance to chromate. While all the genomes share a large number of core proteins (2,810 proteins), the two fastest chromate reducers (Cr-K29 and Cr-K32) shared an additional 610 proteins. All four isolates contain putative genes related to chromate reduction (i.e. chrR and yieF) but their sequences had low homology when compared to other chromate reducing bacteria. We predict both genes may be involved in chromate reduction with one driving reduction and the other providing low levels of resistance. This study illustrates the lack of conservation of chromate reductases and the need for greater research into the mechanisms governing chromate cycling in the environment.
