Isolation and characterization of nickel-resistant microflora from serpentine soils of Andaman

Serpentine soils of Andaman Islands, India characteristically contain high levels of nickel, cobalt and chromium and are colonized by indigenous nickel-hyperaccumulating plants. Attempts have been made to isolate and characterize nickel-resistant microorganisms from these hitherto unexplored naturally nickel-percolated soils. The majority of the nickel-resistant organisms showed a minimum inhibitory concentration (MIC) of Ni2+ ranging from 300 to 400 mg/l and about 3.4% of the total 89 isolates representing bacterial strains were able to grow at 400 mg/l Ni2+. The potent Ni2+-resistant strains AND305 and AND603 were tentatively identified as Pseudomonas spp. and strain AND408 as Bacillus sp. following detailed analysis of morphological and physio-biochemical characteristics. Growth kinetics of these Ni2+-resistant bacteria showed a prolonged lag phase in Ni2+-containing media, which extended with increasing nickel concentration. In addition to Ni2+, these isolates were also resistant to Co2+, Cd2+, Cr6+, Fe3+, Cu2+, Mg2+, Mn2+(50–200 mg/l) and Hg2+ (0.5–2.0 mg/l) and the multiple metal-resistance of the isolates were also associated with the resistance to antibiotics ampicillin, cycloserine and penicillin G.