Determinants for the Activation and Autoinhibition of the Diguanylate Cyclase Response Regulator WspR

ABSTRACT WspR is a hybrid response regulator-diguanylate cyclase that is phosphorylated by the Wsp signal transduction complex in response to growth of Pseudomonas aeruginosa on surfaces. Active WspR produces cyclic di-GMP (c-di-GMP), which in turn stimulates biofilm formation. In previous work, we found that when activated by phosphorylation, yellow fluorescent protein (YFP)-tagged WspR forms clusters that are visible in individual cells by fluorescence microscopy. Unphosphorylated WspR is diffuse in cells and not visible. Thus, cluster formation is an assay for WspR signal transduction. To understand how and why WspR forms subcellular clusters, we analyzed cluster formation and the enzymatic activities of six single amino acid variants of WspR. In general, increased cluster formation correlated with increased in vivo and in vitro diguanylate cyclase activities of the variants. In addition, WspR specific activity was strongly concentration dependent in vitro, and the effect of the protein concentration on diguanylate cyclase activity was magnified when WspR was treated with the phosphor analog beryllium fluoride. Cluster formation appears to be an intrinsic property of phosphorylated WspR (WspR-P). These results support a model in which the formation of WspR-P subcellular clusters in vivo in response to a surface stimulus is important for potentiating the diguanylate cyclase activity of WspR. Subcellular cluster formation appears to be an additional means by which the activity of a response regulator protein can be regulated. IMPORTANCE Bacterial sensor proteins often phosphorylate cognate response regulator proteins when stimulated by an environmental signal. Phosphorylated response regulators then mediate an appropriate adaptive cellular response. About 6% of response regulator proteins have an enzymatic domain that is involved in producing or degrading cyclic di-GMP (c-di-GMP), a molecule that stimulates bacterial biofilm formation. In this work, we examined the in vivo and in vitro behavior of the response regulator-diguanylate cyclase WspR. When phosphorylated in response to a signal associated with surface growth, WspR has a tendency to form oligomers that are visible in cells as subcellular clusters. Our results show that the formation of phosphorylated WspR (WspR-P) subcellular clusters is important for potentiating the diguanylate cyclase activity of WspR-P, making it more active in c-di-GMP production. We conclude that oligomer formation visualized as subcellular clusters is an additional mechanism by which the activities of response regulator-diguanylate cyclases can be regulated.

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Cellular L-arginine pools modulate c-di-GMP turnover and biofilm formation in Pseudomonas putida

10.5194/biofilms9-130 ◽

2020 ◽

Author(s):

Laura Barrientos-Moreno ◽

María Antonia Molina-Henares ◽

María Isabel Ramos-González ◽

Manuel Espinosa-Urgel

Keyword(s):

Pseudomonas Putida ◽

Biofilm Formation ◽

Response Regulator ◽

Second Messenger ◽

Colony Morphology ◽

Diguanylate Cyclase ◽

Arginine Biosynthesis ◽

Amino Acid Transport System ◽

Metabolic Signal ◽

Biofilm Development

The intracellular second messenger cyclic diguanylate (c-di-GMP) is broadly conserved in bacteria, where it influences processes such as virulence, stress resistance and biofilm development. In the plant-beneficial bacterium Pseudomonas putida KT2440, the response regulator with diguanylate cyclase activity CfcR is the main contributor to c-di-GMP levels in the stationary phase of growth. When overexpressed, CfcR increases c-di-GMP levels and gives rise to a pleiotropic phenotype that includes enhanced biofilm formation and crinkly colony morphology. Our group has previously reported that insertion mutants in argG and argH, the genes that encode the last two enzymes in the arginine biosynthesis pathway, do not display the crinkly colony morphology phenotype and show decreased c-di-GMP levels even in the presence of cfcR in multicopy (Ramos-Gonz&#225;lez, M.I. et al. 2016. Front. Microbiol. 7, 1093). Here we present results indicating that L-arginine acts both as an environmental and as a metabolic signal that influences the lifestyles of P. putida through the modulation of c-di-GMP levels and changes in the expression of structural elements of biofilms. Exogenous L-arginine partially restores c-di-GMP levels in arginine biosynthesis mutants, a response that is transduced through CfcR and possibly (an)other diguanylate cyclase(s). At least three periplasmic binding proteins, each forming part of an amino acid transport system, contribute in different ways to the response to external L-arginine. We propose that the turnover of the second messenger c-di-GMP is modulated by the state of global arginine pools in the cell resulting both from anabolism and from uptake.

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