Identification of halophilic bacteria tolerant to heavy metals

Heavy metals released into the environment cause deterioration of environmental health. Their removal by biological means is a strategy under study. This research aimed to isolate and identify halophilic bacteria from saline-sodic soils and determine their tolerance to the metalloid As3+ and the heavy metals Cr6+, Hg2+, and Pb2+. The strains were grown on halophilic medium (HM), without and with the presence of each metal, at 10% NaCl, pH 8.0 +/- 0.2, and 37 oC. The strains with the highest toler-ance to each metal were identified by 16S rRNA gene sequencing and phylogenetic analysis. The minimum inhibitory concentration (MIC) was subsequently determined. Seventy-five halophilic strains were isolated. The isolates with the highest tolerance were Salinicococcus spp. strains TX3SA-2MHG1 and TX3SA-4MHG1 [MIC (Hg2+) of 0.1 mmol/L]; Halomonas sp. strain TXO4B-1SG9 [MIC (Pb2+) of 7.0 mmol/L]; No-cardiopsis sp. strains TXO7B-1SG12 and TXV10-3SG5 [MIC (As3+) of 8.5 mmol/L], and Nocardiopsis sp. strain TXV7-8SG2 [MIC (As3+) of 27.25 mmol/L; MIC (Cr6+) 1250.0 mmol/L; MIC (Hg2+) 0.075 mmol/L and MIC (Pb2+) 7.5 mmol/L]. It was pos-sible to obtain and identify isolates of halophilic metal tolerant bacteria.