EVOLUTION OF SALMONELLA COPPER RESISTANCE AND ITS ROLE IN VIRULENCE

MÉNDEZ AAE; MENDOZA JI; ECHARREN ML; CHECA SK; SONCINI FC

VIRTUAL

Congreso; LVII SAIB Meeting - XVI SAMIGE Meeting; 2021

SOCIEDAD ARGENTINA DE BIOQUIMICA Y BIOLOGIA MOLECULAR Y SOCIEDAD ARGENTINA DE MICROBIOLOGIA GENERAL

Salmonella enterica is a species that includes a large group of food-borne and facultative intracellular pathogens causing infections that ranges from self-limited gastroenteritis to severe invasive illness in susceptible hosts. Among them, S. Typhimurium serovar is the best studied member. During its infective cycle, Salmonella adapts to and survive in different conditions, including the menacing host environment. This reflects the versatility of its genetic repertoire. Several regulatory systems have been described to perceive and respond to specific host?s signals modulating the expression of essential virulence factors. In particular, it has been shown that this pathogen detects the surge of copper (Cu) inside the Salmonella-containing vacuole (SCV) in infected cells. In this context, mutants affected in Cu-resistance show a reduced survival in macrophages comparing with the wild-type strain. Most known bacterial cuproproteins localize to the patogen´s cell envelope, which makes this compartment the main target for Cu toxicity. While most enteric species rely on the CusR/CusS-controlled CusCFBA efflux system to maintain the periplasmic Cu homeostasis, we noticed that this sensory and efflux system, encoded in the cus locus, is absent in the genome of most Salmonella subspecies. Still, small and diverse remnants of the outmost cus locus genes can be identified in most genomes, suggesting that different deletion events took place during Salmonella evolution. Interestingly, these pathogenic bacteria acquired cueP, a species-specific CueR/CpxRS-coregulated gene, coding for a periplasmic Cu-chaperone that is essential for Cu-resistance under anaerobic conditions, as CusCFBA in other species. Although the reasons for gaining cueP and a subsequent loss of the ancestral cus locus are not clear, we hypothesized that virulence could be the cause. In this study, we reintroduced the E. coli cus locus in the identified cus-scar present in the S. Typhimurium genome and evaluated its role in Cu resistance and in virulence, both in an otherwise wild-type or in a ΔcueP backgrounds. As previously reported for CueP, the presence of the cus locus did not affect Salmonella Cu-resistance under aerobic conditions but increased Cu-tolerance under anaerobic conditions, irrespective of the presence or absence of CueP. Interestingly, Cu-dependent transcriptional induction of cueP and cusCFBA occurred at different stages of growth, and irrespective of the presence or absence of the cus locus, only deletion of cueP attenuated virulence in macrophages. These results indicate that CueP and CusCFBA exert redundant functions for metal resistance, but they fulfil different roles during macrophage replication and therefore in virulence.