Effects of ISSo2 insertions in structural and regulatory genes of the trimethylamine oxide reductase of Shewanella oneidensis.

We have isolated three Shewanella oneidensis mutants specifically impaired in trimethylamine oxide (TMAO) respiration. The mutations arose from insertions of an ISSo2 element into torA, torR, and torS, encoding, respectively, the TMAO reductase TorA, the response regulator TorR, and the sensor TorS. Although TorA is not the sole enzyme reducing TMAO in S. oneidensis, growth analysis showed that it is the main respiratory TMAO reductase. Use of a plasmid-borne torE'-lacZ fusion confirmed that the TorS-TorR phosphorelay mediates TMAO induction of the torECAD operon.