Induced Adaptation as a Means of Sustained Mercury Tolerance in Bacillus subtilis

Heavy metals are known to possess toxic effect against prokaryotes as well as eukaryotes. Bacillus subtilis, a gram-positive bacterium, finds several useful applications such as biofertilization and antibiosis, but such applications get compromised due to limited bacterial survival during heavy metal stress. In the present study, experimental measures for natural adaptation of these bacteria to high Hg2+ concentration were performed by serially treating them with lower to higher Hg2+ concentration. Also, same adaptive ability and sustained growth were observed at high Hg2+ concentration after a year of induction thereby confirming adaptive success. Analysis of catalase and superoxide dismutase activity showed increased enzymatic activity as a means of survival under metal stress. Proteomic profiling was observed by SDS-PAGE indicating expression of differential proteins in adapted strains. Less malondialdehyde content in adapted strains showed restoration of membrane integrity which was also evident in SEM analysis showing smoother cell surface. Such successful adaptation induced in Bacillus subtilis paves way for agricultural and environmental applications of such strains in metal-stressed regions.