ABSTRACTPrtA is the major secreted metalloprotease ofSerratia marcescens. Previous reports implicate PrtA in the pathogenic capacity of this bacterium. PrtA is also clinically used as a potent analgesic and anti-inflammatory drug, and its catalytic properties attract industrial interest. Comparatively, there is scarce knowledge about the mechanisms that physiologically govern PrtA expression inSerratia. In this work, we demonstrate that PrtA production is derepressed when the bacterial growth temperature decreases from 37°C to 30°C. We show that this thermoregulation occurs at the transcriptional level. We determined that upstream ofprtA, there is a conserved motif that is directly recognized by the CpxR transcriptional regulator. This feature is found alongSerratiastrains irrespective of their isolation source, suggesting an evolutionary conservation of CpxR-dependent regulation of PrtA expression. We found that inS. marcescens, the CpxAR system is more active at 37°C than at 30°C. In good agreement with these results, in acpxRmutant background,prtAis derepressed at 37°C, while overexpression of the NlpE lipoprotein, a well-known CpxAR-inducing condition, inhibits PrtA expression, suggesting that the levels of the activated form of CpxR are increased at 37°C over those at 30°C. In addition, we establish that PrtA is involved in the ability ofS. marcescensto develop biofilm. In accordance, CpxR influences the biofilm phenotype only when bacteria are grown at 37°C. In sum, our findings shed light on regulatory mechanisms that fine-tune PrtA expression and reveal a novel role for PrtA in the lifestyle ofS. marcescens.IMPORTANCEWe demonstrate thatS. marcescensmetalloprotease PrtA expression is transcriptionally thermoregulated. While strongly activated below 30°C, its expression is downregulated at 37°C. We found that inS. marcescens, the CpxAR signal transduction system, which responds to envelope stress and bacterial surface adhesion, is activated at 37°C and able to downregulate PrtA expression by direct interaction of CpxR with a binding motif located upstream of theprtAgene. Moreover, we reveal that PrtA expression favors the ability ofS. marcescensto develop biofilm, irrespective of the bacterial growth temperature. In this context, thermoregulation along with a highly conserved CpxR-dependent modulation mechanism gives clues about the relevance of PrtA as a factor implicated in the persistence ofS. marcescenson abiotic surfaces and in bacterial host colonization capacity.
CpxR-Dependent Thermoregulation ofSerratia marcescensPrtA Metalloprotease Expression and Its Contribution to Bacterial Biofilm Formation
