Reduction of chromate by microorganisms isolated from metal contaminated sites of Karachi, Pakistan

Three bacterial strains, two identified as Pseudomonas stutzeri and one as a strain of cucurbit yellow vine disease bacterium, isolated from a foundry soil and a tannery, respectively, in Pakistan, were resistant to up to 1 m M chromate and anaerobically reduced Cr(VI) up to 100 mu M. The highest rem oval was by P. stutzeri CMG463: 88 mu mol l(-1) (88% of that supplied; spec ific rate was 3.0 nmol mg(-1) protein h(-1)), while 58 and 76 mu mol l(-1) (58% and 76%) were removed by P. stutzeri CMG462 and cucurbit yellow vine d isease bacterium CMG480, respectively. These isolates were compared to stra ins isolated from an uncontaminated coastal site in the UK and designated a s K2 (Pseudomonas synxantha) K3 (Bacillus sp.), and J3 (unidentified Gram-p ositive strain). Strain K3 was Cr-sensitive, partially lysed by Cr(VI), but had the highest removal of chromate anaerobically: 92 mu mol l(-1) (92% of that supplied) at a specific rate of 71 nmol mg(-1) protein h(-1). Analysi s of cell sections using transmission electron microscopy with energy dispe rsive X-ray analysis showed intracellular chromium in P. stutzeri but the c ucurbit yellow vine disease bacterium and the Bacillus sp. precipitated chr omium extracellularly. The isolates from the Cr-contaminated sites did not remove more Cr(VI), overall, than Cr-unstressed bacteria, but their toleran ce to Cr(VI) is potentially useful for bioremediation, particularly since o ther studies have shown that the two P. stutzeri strains can bioaccumulate Cu2+.