Identification of halophilic bacteria tolerant to heavy metals

Abstract

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 tolerance 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]; Nocardiopsis 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 possible to obtain and identify isolates of halophilic metal tolerant bacteria.