As in the case for Arth_4252, orthologs of Arth_4247 are also present near chrA orthologs in Arthrobacter sp. strain CHR15 (81% similarity to ORF 27) and C. metallidurans (52% similarity to Rmet_6195). Arth_4255 encodes a putative malate:quinone oxidoreductase of 517 aa with 77% similarity to Arthrobacter

aurescens TC1 Mqo. This class of proteins generally functions in energy production, but the biochemical role of Arth_4255 in the context of Cr(VI) resistance is not known. In Agrobacterium tumefaciens, insertional inactivation of an operon specifying NADH:quinone oxidoreductases similar to malate:quinone oxidoreductases (MrpA, MrpC and MrpD) resulted in the loss of arsenite oxidation. The phenotype was JSH-23 solubility dmso recovered via complementation with the intact Mrp operon [33]. In other bacteria, NADH-dependent oxidoreductases have been shown to reduce Cr(VI) [34]; however, there is no conclusive evidence of Cr(VI) reduction in FB24, and it is unlikely that Arth_4255 is a Cr(VI) reductase.

Loss of plasmid DNA from strain FB24 results in metal sensitivity and increased intracellular chromium accumulation A chromate-sensitive mutant (D11) was obtained after successive culturing of FB24 for 90 generations in the absence of chromate. Loss of plasmid DNA was assessed by Southern hybridization using a 10.6-kb probe PRN1371 purchase for the CRD, and the results were validated by a PCR screen using gene-specific primers (data not shown). Strain D11 was hypersensitive to low

levels (0.5 mM), whereas the wild type grew prolifically on 0.1X nutrient agar (NA) plates amended with 5 mM chromate. Strain D11 was also very sensitive to lead, zinc and cadmium. Jerke et al (2008) had shown that FB24 contained 3 plasmids, each with genes that confer resistance to lead, zinc and cadmium [35]. Whereas FB24 attained maximal cell densities in 200 μM lead, zinc and cadmium in mXBM, growth of strain D11 was strongly inhibited by 10 μM lead, 50 μM zinc and 1 μM cadmium (data not shown). Total intracellular chromium content was measured in chromate-exposed cells GNA12 of FB24 and D11 to determine if the loss of Cediranib chromate resistance in strain D11 correlated with increased intracellular accumulation of chromium. There was a significant difference (p = 0.015) in chromium content between strain D11 (2.8 × 10-7 mol mg protein-1) and FB24 (9.2 × 10-8 mol mg protein-1). Chromium was undetectable in FB24 and D11 cells that were not exposed to chromate. Similar decreases in chromium accumulation were found between chromate-resistant and -sensitive strains of P. aeruginosa and C. metallidurans which contain ChrA efflux pumps [15, 36]. The comparable change in chromium accumulation between resistant and sensitive strains of Arthrobacter sp.