Abstract
The second messenger cyclic di-GMP (c-di-GMP) is a key molecule that controls different physiological and behavioral processes in many bacteria, including motile-to-sessile lifestyle transitions. Although the external stimuli that modulate cellular c-di-GMP contents are not fully characterized, there is growing evidence that certain amino acids act as environmental cues for c-di-GMP turnover. In the plant-beneficial bacterium Pseudomonas putida KT2440, both arginine biosynthesis and uptake influence second messenger contents and the associated phenotypes. To further understand this connection, we have analyzed the role of ArgR, which in different bacteria is the master transcriptional regulator of arginine metabolism but had not been characterized in P. putida. The results show that ArgR controls arginine biosynthesis and transport, and an argR-null mutant grows poorly with arginine as the sole carbon or nitrogen source and also displays increased biofilm formation and reduced surface motility. Modulation of c-di-GMP levels by exogenous arginine requires ArgR. The expression of certain biofilm matrix components, namely, the adhesin LapF and the exopolysaccharide Pea, as well as the diguanylate cyclase CfcR is influenced by ArgR, likely through the alternative sigma factor RpoS. Our data indicate the existence of a regulatory feedback loop between ArgR and c-di-GMP mediated by FleQ. IMPORTANCE Identifying the molecular mechanisms by which metabolic and environmental signals influence the turnover of the second messenger c-di-GMP is key to understanding the regulation of bacterial lifestyles. The results presented here point at the transcriptional regulator ArgR as a central node linking arginine metabolism and c-di-GMP signaling and indicate the existence of a complex balancing mechanism that connects cellular arginine contents and second messenger levels, ultimately controlling the lifestyles of Pseudomonas putida.