A metallothionein and CPx-ATPase handle heavy-metal tolerance in the filamentous cyanobacterium Oscillatoria brevis.

A metallothionein (BmtA) and a CPx-ATPase (Bxa1) have been identified and characterized from the cyanobacterium Oscillatoria brevis. Both bmtA and bxa1 expression can be markedly induced in vivo by Zn(2+) or Cd(2+). Over-expression of bmtA or bxa1 in Escherichia coli enhances Zn(2+) and Cd(2+) tolerance in the transformant. Dynamic studies on the expression of two genes showed that the maximum expression of bxa1 induced by Zn(2+) and Cd(2+) was much quicker than that of bmtA, suggesting distinct physiological roles of metallothionein and CPx-ATPase in the handling of surplus metal.