CONICET | Buscador de Institutos y Recursos Humanos

Serratia marcescens (Sma) is an environmentally ubiquitous bacterium also acting as an opportunistic pathogen. Moreover, Sma displays biofilm formation capacity that has been shown to be related to its ability to colonize, persist, and proliferate on either biological or inert surfaces. This capacity to adapt and survive in either hostile or changing environments can be related to the expression of numerous secreted hydrolytic enzymes, including proteases. Genomic analysis of Sma clinical strain RM66262 identified four zinc-metalloprotease-encoding genes. Amongst them, we previously showed that PrtA is the most abundant in the secretome and its expression depends on the bacterial growth temperature, being transcriptionally upregulated at 30°C in comparison with 37°C. Considering this, we examined whether PrtA could influence Sma biofilm formation capacity. To that aim, we performed in vitro biofilm assays in polystyrene microwell plates, followed by biofilm quantitation using crystal violet staining. When the strains were grown at 30°C or 37°C in SLB medium the lack of PrtA expression in the prtA strain reduced the capacity of the bacteria to form biofilm compared with that of the wild-type strain, being more attenuated at 37°C. Results of confocal microscopy also showed biofilm formation deficiency in the prtA strain. This defect could be complemented to wild-type levels by adding catalytically active purified PrtA. To further understand PrtA influence on biofilm formation, we built a single-aminoacid-mutant protein that annuls the protease hydrolytic capacity and performed biofilm assays. This resulted in a defective biofilm phenotype that could also be rescued by the addition of catalytically active PrtA. In sum, our results demonstrate that PrtA expression and activity contribute to the ability of Sma to structure a biofilm community