LAUSR

Five heavy metals were introduced into the bacterial heavy metal resistance tests. The results showed that apparent inhibition effects of Cd2+ and Cu2+ on the growth of Acidithiobacillus ferrooxidans BYSW1 occurred at high concentrations (>0.04 mol l-1). Significant differences (P < 0.001) were both noticed in the expression of two ferredoxin-encoding genes (fd-I and fd-II) related to heavy metal resistance in the presence of Cd2+ and Cu2+ . When exposed to 0.06 mol l-1 Cd2+, the relative expression levels of fd-I and fd-II were about 11 and 13 times as much as those of the control, respectively. Similarly, exposure to 0.04 mol l-1 Cu2+ caused approximate 8 and 4 times higher than those of the control, respectively. These two genes were cloned and expressed in Escherichia coli, and the structures, functions of two corresponding target proteins, i.e. Ferredoxin-I (Fd-I) and Ferredoxin-II (Fd-II), were predicted. The recombinant cells inserted by fd-I or fd-II were more resistant to Cd2+ and Cu2+ compared with wild-type cells. This study was the first investigation regarding the contribution of fd-I and fd-II to enhancing heavy metal resistance of this bioleaching bacterium, and laid a foundation for further elucidation of heavy metal resistance mechanisms caused by Fd.