SlpE METALLOPROTEASE OF Serratia marcescens IS REGULATED BY IRON AND IS EXPRESSED WITHIN EPITHELIAL CELLS

DAVID CURA MICHELINO; ELEONORA GARCÍA VÉSCOVI; JAVIER FERNANDO MARISCOTTI

Rosario

Congreso; LIX Annual Meeting SAIB 2023; 2023

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB)

Serratia marcescens is an opportunistic humans pathogen and is widely distributed in the environment and a broad range of host organisms. In humans, it causes a variety of infections with increasing incidence, primarily due to the acquisition of antibiotic resistance mechanisms, the ability to survive for months on inanimate surfaces, and resistance to conventional disinfection procedures. Despite its clinical prevalence, the factors and mechanisms contributing to Serratia pathogenicity remain unclear. S. marcescens ability to adapt and survive in hostile or changing environments is related to the bacterial capacity to express a wide range of secreted enzymes, including chitinases, phospholipase, hemolysin, nuclease, and proteases, including the metalloprotease SlpE produced in our clinical isolate. Recent studies showed that SlpE is secreted by the LipBCD transporter, highlighting this enzyme as an important virulence factor in cell line cultures. SlpE is found in our clinical isolate RM66262 and in most clinical isolates, but it is absent in most non-clinical isolates, including the reference strain Db11 of S. marcescens. However, little is known about the environmental signals and regulatory factors that modulate its production. In this study, we evaluated the regulation of the metalloprotease SlpE using a GFP-containing reporter plasmid. The results showed that SlpE expression is induced during the stationary growth phase, although its expression levels are five times lower than the major protease PrtA at 30ºC. One defense mechanism of vertebrate hosts against bacterial infection is nutrient deprivation to prevent bacterial growth, a process known as nutritional immunity. The most significant form of nutritional immunity is iron sequestration. We found that under iron-depleted conditions, PslpE-gfp transcription levels are five times higher than in iron-rich medium, reaching levels equivalent to prtA expression at 30ºC. Furthermore, our results suggest that this increase in SlpE expression levels depends on the ferric uptake regulator (Fur). Here, we also analyzed the expression of reporter plasmids through immunofluorescence and flow cytometry, demonstrating that S. marcescens induces the intracellular expression of SlpE during the invasion of epithelial cells. Additionally, we observed that this induction is partially reversed upon supplementing the medium of the epithelial cells with iron. These findings suggest that S. marcescens SlpE is involved in proteolytic activity under iron-limiting conditions within the intracellular host niche.