CpxR-dependent thermoregulation of Serratia marcescens PrtA metalloprotease expression and its contribution to bacterial biofilm formation

BRUNA, R.; MOLINO, MV; LAZZARO, M.; MARISCOTTI, J.F.; GARCÍA VÉSCOVI, E.

JOURNAL OF BACTERIOLOGY

AMER SOC MICROBIOLOGY

Lugar: Washington; Año: 2018 vol. 200

0021-9193

ABSTRACT PrtA is the major secreted metalloprotease of Serratia marcescens. Previousreports implicate PrtA in the pathogenic capacity of this bacterium. PrtA is alsoclinically used as a potent analgesic and anti-inflammatory drug, and its catalyticproperties attract industrial interest. Comparatively, there is scarce knowledge aboutthe mechanisms that physiologically govern PrtA expression in Serratia. In this work,we demonstrate that PrtA production is derepressed when the bacterial growthtemperature decreases from 37°C to 30°C. We show that this thermoregulation occursat the transcriptional level. We determined that upstream of prtA, there is aconserved motif that is directly recognized by the CpxR transcriptional regulator.This feature is found along Serratia strains irrespective of their isolation source, suggestingan evolutionary conservation of CpxR-dependent regulation of PrtA expression.We found that in S. marcescens, the CpxAR system is more active at 37°C thanat 30°C. In good agreement with these results, in a cpxR mutant background, prtA isderepressed at 37°C, while overexpression of the NlpE lipoprotein, a well-knownCpxAR-inducing condition, inhibits PrtA expression, suggesting that the levels of theactivated form of CpxR are increased at 37°C over those at 30°C. In addition, we establishthat PrtA is involved in the ability of S. marcescens to develop biofilm. In accordance,CpxR influences the biofilm phenotype only when bacteria are grown at37°C. In sum, our findings shed light on regulatory mechanisms that fine-tune PrtAexpression and reveal a novel role for PrtA in the lifestyle of S. marcescens.IMPORTANCE We demonstrate that S. marcescens metalloprotease PrtA expressionis transcriptionally thermoregulated. While strongly activated below 30°C, its expressionis downregulated at 37°C. We found that in S. marcescens, the CpxAR signaltransduction system, which responds to envelope stress and bacterial surface adhesion,is activated at 37°C and able to downregulate PrtA expression by direct interactionof CpxR with a binding motif located upstream of the prtA gene. Moreover,we reveal that PrtA expression favors the ability of S. marcescens to develop biofilm,irrespective of the bacterial growth temperature. In this context, thermoregulationalong with a highly conserved CpxR-dependent modulation mechanism gives cluesabout the relevance of PrtA as a factor implicated in the persistence of S. marcescenson abiotic surfaces and in bacterial host colonization capacity.