Summary: Mxd regulation in S. oneidensis MR-1. Summary of mxd regulation in S. oneidensis MR-1 under planktonic (left cartoon) and biofilm (right cartoon) conditions. Under planktonic conditions starvation and more specifically carbon starvation was identified to transcriptionally induce expression of the mxd operon. The ArcS/ArcA TCS was found to act as a minor repressor of the mxd genes under planktonic conditions. The TCS BarA/UvrY was identified to induce mxd gene expression under planktonic growth conditions. Under biofilm conditions, the ArcS/ArcA TCS activates mxd gene expression which is contrary to the findings under planktonic conditions. The TCS BarA/UvrY was found to act as a minor inducer of biofilm formation (solid arrow) and it remains to be determined if it acts via the mxd operon (dashed arrow).