Increased Proteolytic Activity of Serratia marcescens Clinical Isolate HU1848 Is Associated with Higher eepR Expression

is a global opportunistic pathogen. cytotoxicity of this bacterium is mainly related to metalloprotease serralysin (PrtS) activity. Proteolytic capability varies among the different isolates. Here, we characterized protease production and transcriptional regulators at 37°C of two isolates from bronchial expectorations, HU1848 and SmUNAM836. As a reference strain the insect pathogen Db10 was included. Zymography of supernatant cultures revealed a single (SmUNAM836) or double proteolytic zones (HU1848 and Db10). Mass spectrometry confirmed the identity of PrtS and the serralysin-like protease SlpB from supernatant samples. Elevated proteolytic activity and expression were evidenced in the HU1848 strain through azocasein degradation and qRT-PCR, respectively. Evaluation of transcriptional regulators revealed higher expression in HU1848, whereas and transcriptional levels were similar between studied strains. Higher expression in HU1848 was further confirmed through an transcriptional assay. Moreover, two putative CpxR binding motifs were identified within the regulatory region. EMSA validated the interaction of CpxR with both motifs. The evaluation of transcription in a deletion strain indicated that CpxR negatively regulates . Sequence conservation suggests that regulation of by CpxR is common along species. Overall, our data incorporates CpxR to the complex regulatory mechanisms governing expression and associates the increased proteolytic activity of the HU1848 strain with higher transcription. Based on the global impact of EepR in secondary metabolites production, our work contributes to understanding virulence factors variances across isolates.