Isolation and identification of cadmium- and lead-resistant lactic acid bacteria for application as metal removing probiotic

The purpose of the present study was to isolate and identify the metal-resistant lactic acid bacteria from sediments of coastal aquaculture habitats for removal of cadmium and lead from ambience. Collected sediment samples were used to isolate the cadmium- and lead-resistant bacterial colonies by spread plate technique using agar media (De Man, Rogosa and Sharpe) supplemented with cadmium or lead at 50 mg/l. Isolates were identified by bacterial colony polymerase chain reaction and sequencing of 16S ribosomal deoxyribonucleic acid. Metal removing probiotic was determined by characterizing the lactic acid yield in culture media, viability in fish intestine, metal-resistant and metal-removal efficiencies. 16S ribosomal deoxyribonucleic acid sequencing data of five (Cd10, Cd11, Pb9, Pb12 and Pb18) and other all isolates clearly showed 99 % similarities to Enterococcus faecium and Bacillus cereus, respectively. The Pb12 exhibited higher lactic acid yield (180 mmol) than that of the remaining E. faecium strains and excellent viability without pathogenicity; therefore, further study was carried out using Pb12 strain. The selected Pb12 strain showed elevated metal resistant (minimum inhibitory concentrations 120 and 800 mg/l for cadmium and lead, respectively) and removal efficiencies [Cadmium 0.0377 mg/h/g and lead 0.0460 mg/h/g of cells (wet weight)]. From the viability and metal removal points of view, it can be concluded that isolated metal-resistant E. faecium Pb12 strains might be used as potential probiotic strains for removing heavy metals from fish intestinal milieu to control the progressive bioaccumulation of heavy metals in the fish.