ORF319, A SPI-2 ENCODED SALMONELLA-SPECIFIC ANTIVIRULENCE FACTOR THAT CONTROLS BIOFILM FORMATION

VICTOR HOREN L; CISANA P; 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

Cellulose is a major component of the Salmonella biofilm extracellular matrix. It is considered an antivirulence factor because it interferes with Salmonella proliferation inside macrophages and virulence in mice. Its synthesis is stimulated by CsgD, the master regulator of biofilm extracellular matrix formation in enterobacteria. We previously identified a SPI-2 encoded, Salmonella-specific transcription factor, MlrB, that inside host cells represses transcription of csgD and its downstream gene, orf319. Although the function of Orf319 is unknown and deletion of its coding gene has no defect either in biofilm formation or in macrophages survival, its overexpression substantially increases extracellular matrix production, induces csgD transcription and reduces Salmonella proliferation inside macrophages. We propose that Orf319 functions as an antivirulence factor through the control of cellulose production, as deletion of the cellulose synthase coding gene bcsA restored the proliferation in macrophages of a biofilm overproducing Salmonella mutant strain. Surprisingly, Orf319 effect on biofilm formation and on csgD expression did not require the presence of MlrB or of any other identified factors regulating csgD transcription, including MlrA, a key csgD transcriptional activator. These observations suggest a direct role of Orf319 in the transcriptional control of the biofilm master regulator. In silico analysis shows the presence of two cysteine residues that are conserved in Orf319 homologues. Alanine substitution of these residues abrogated both csgD activation and biofilm formation, indicating their relevance for Orf319 biological function. Our findings provide a novel link between the SPI-2 coding factors in the control of Salmonella virulence and the production of extracellular matrix.