Responses of bacteria to heavy-metal-stress and its Influence on the antioxidant enzymes activity

The aims of this study, Bacillus subtilis, Aeromonas salmonicida, Exiguobacterium aurantiacum and Burkholderia cepacia were isolated from Marchica lagoon in Morocco, and studied their resistance toward heavy metals (Cd^2+, Cr^6+, Ag^+, Cu^2+ and Hg^2+) and antibiotics. Effects of the metals on growth kinetics of strains and the antioxidant enzymes activities produced by some strains were evaluated. The minimal inhibitory concentrations (MIC) of the metals at variant concentrations (10-38 mM) were determined in liquid and solid medium. Thus, the obtained results in solid medium were higher than those in liquid medium. Strains were showed an extreme resistance against metals with the MIC values of Cu (9 mM), Cd (6.25 mM) and Cr (2.5 mM). Meanwhile, different concentrations of Cd had stimulated and increased the activity of catalase and superoxide dismutase in Bacillus subtilis, whereas the activity of these enzymes decreased when used 2mM of Cd in Burkholderia cepacia