T2SS OF Serratia marcescens PROMOTES THE ELIMINATION OF MICROBIAL COMPETITORS

SARTORI, MS; GARCÍA VÉSCOVI, E.; MARISCOTTI, J.F.

Córdoba

Congreso; XVII Congreso Argentino de Microbiología General; 2022

SAMIGE

Serratia marcescens is an opportunistic human pathogen that represents a growing problem for public health, particularly in hospitalized or immunocompromised patients. Despite its clinical prevalence, factors and mechanisms that contribute to Serratia pathogenesis remain unclear. S. marcescens ability to adapt to and survive in either hostile or changing environments also relates to the bacterial capacity to express a wide range of secreted enzymes, including chitinases, phospholipase, haemolysin, nuclease and proteases. The type II secretion system (T2SS) is a multiprotein secretion complex, present in a wide variety of organisms and frequently implicated in virulence. In our clinical RM66262 strain, we found the presence of a T2SS, which is chromosomally encoded in the majority of clinical isolates, but is absent from most non-clinical isolates including S. marcescens Db11, a reference strain. However, the substrates of the RM66262 T2SS, environmental signals and regulatory factors that modulate its expression are unknown. The objective of this work is to determine the role of T2SS in S. marcescens RM66262. We have assessed the regulation of T2SS using a gfp-containing reporter plasmid. Results showed that T2SS expression is induced during the stationary growth phase. One conspicuous defense of vertebrates against bacterial infections is nutrient deprivation, which prevents bacterial growth in a process termed nutritional immunity. The most significant form of nutritional immunity is the sequestration of iron. We found that under iron-depleted conditions, the transcription levels of PT2SS-gfp is two-times increased than in iron-suppled medium. Performing killing assays between S. marcescens RM66262 and E. coli, P. aeruginosa or S. marcescens Db11, we have determined that T2SS contributes, together with T6SS, to inter-species and intra-species elimination of microbial competitors. In addition, we found that that T2SS expression is five-times increased when S. marcescens RM66262 was challenged in competition assays using Acinetobacter nosocomialis as attacker. Taken together, our results suggest that in S. marcescens the regulated expression of T2SS would constitute a survival strategy in bacterial competition.