Expressional regulation of a novel organomercurial lyase gene encoded in the mercury resistance module of TnMERI1 from Bacillus megaterium MB1

TnMERI1 is a broad-spectrum mercury resistance transposon identified in a G ram-positive bacterium, Bacillus megaterium MB1. The mercury resistance mod ule (mer operon) encoded in TnMERI1, which confers resistance to many organ omercurials, was identified and the complete structure of the module was cl arified. The module is complicated because three organomercurial lyase gene s (merB genes) and two regulator genes (merR genes) are encoded in the resi stance module. Upstream the merR 1, a novel organomercurial lyase, merB3, w as identified and was found to have its own operator/promoter region. In th is study, we constructed a series of mer operon-luciferase (mer-lux) transc riptional fusion plasmids to evaluate the gene expression of merB3 in vivo. The results showed that both MerR1 and MerR2 repressed the transcriptional expression of merB3 when no mercurial inducer was added. However, the posi tive transcriptional regulation (activation) mediated by MerR1 is stronger than MerR2 when mercury chloride was applied as an inducer. Therefore, it i s concluded that merR1 is a primary and direct regulator gene for the expre ssion of merB3.