Contribution of the ligand binding protein RmcM and the alternative sigma factor RpoN to c-di-GMP signaling in Stutzerimonas stutzeri MJL19

Cyclic diguanylate (c-di-GMP) is an ubiquitous second messenger in bacteria. Intracellular levels and/or local pools of this molecule modulate a diversity of processes in response to environmental and metabolic signals, including the transition between the motile unicellular mode of life and the biofilm lifestyle. Proteins involved in the synthesis and degradation of this second messenger, and in the response to c-di-GMP, have been characterized in different species, but there are still significant knowledge gaps, particularly in less studied bacteria. In this work, we have focused on a predicted diguanylate cyclase of Stutzerimonas stutzeri MJL19 containing a periplasmic ligand binding domain. This protein, which we have named RmcM, binds two structurally similar amino acid derivatives, γ-aminobutyric acid (GABA) and 5-aminovaleric acid, with high affinity, modulating c-di-GMP contents in response to these two ligands. Deletion of rcmM caused an increase of motility, while surprisingly also leading to a transient increase in global second messenger under some environmental conditions. In contrast, rmcM in a multicopy plasmid leads to increased c-di-GMP levels. In the course of this work, evidences were also obtained on the regulatory role of the alternative sigma factor RpoN on c-di-GMP turnover and the associated phenotypes in this strain.