Abstract
A total of 16 different strains of Microbacterium spp. were isolated from contaminated soil and enriched on the carcinogen, hexavalent chromium [Cr(VI)]. The majority of the isolates (11 of the 16) were able to tolerate concentrations (0.1 mM) of cobalt, cadmium, and nickel, in addition to Cr(VI) (0.5–20 mM). Interestingly, these bacteria were also able to tolerate three different antibiotics (ranges: ampicillin 0–16 μg ml−1, chloramphenicol 0–24 μg ml−1, and vancomycin 0–24 μg ml−1). To gain genetic insight into these tolerance pathways, the genomes of these isolates were assembled and annotated. The genomes of these isolates not only have some shared genes (core genome) but also have a large amount of variability. The genomes also contained an annotated Cr(VI) reductase (chrR) that could be related to Cr(VI) reduction. Further, various heavy metal tolerance (e.g., Co/Zn/Cd efflux system) and antibiotic resistance genes were identified, which provide insight into the isolates’ ability to tolerate metals and antibiotics. Overall, these isolates showed a wide range of tolerances to heavy metals and antibiotics and genetic diversity, which was likely required of this population to thrive in a contaminated environment.
Highlights
Heavy metals, while naturally occurring, cause harm to both human and ecosystem health
The objective of this study was to examine the genomes of 16 Microbacterium spp. strains isolated from metal contaminated soil to identify their genetic potential and physiological ability to reduce Cr(VI) and to tolerate both heavy metals and antibiotics
Bacterial isolation Isolation of Microbacterium spp. from soil is described in Kourtev, Nakatsu & Konopka (2009) and Henson et al (Henson et al, 2015)
Summary
While naturally occurring, cause harm to both human and ecosystem health. Chromium is a mutagen and carcinogen and its presence in the environment can be natural due to anthropogenic activities, such as industrial manufacturing (e.g., metal plating and tanneries) and mining (chromite ore) (Barak et al, 2006; Brose & James, 2010; Cheng, Holman & Lin, 2012). Chromium can exist as hexavalent chromium [Cr(VI)], which is soluble and more toxic, or as insoluble trivalent chromium [Cr(III)] (Bartlett, 1991; Cheng, Holman & Lin, 2012).
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