Arsenic biotransformation by a filamentous cyanobacterium Nostoc sp. PCC7120

摘要

Arsenic is a prevalent environmental toxin and carcinogen, and its toxicity and mobility are determined by arsenic speciation. Microbial biotransformation of arsenic plays an important role in the arsenic biogeo- chemical cycle. Cyanobacteria with a long evolutionary history are widespread in nature. In this paper, Nostoc sp. PCC 7120 was chosen to thoroughly study biotransformation pathways of arsenic. Nostoc sp. PCC 7120 undergoes multiple processes to cope with arsenic. The reduction-oxidation reactions that interconvert arsenate [As(V)] and arsenite [As(III)] form an arsenic redox cycle in Nostoc sp. PCC 7120, and As(III) is then excreted from cells. In addition, Nostoc sp. PCC 7120 has the ability to methylate As(III) and further synthesize arsenosugar, and even demethylate both monomethylarsenate [MAs(V)] and monomethylarsenite [MAs(III)] to As(III). The genes of Nostoc sp. PCC 7120 involved in As(III) methylation and MAs(III) demethylation have also been identified.