Type VI secretion system genes sciG and sciS facilitate biofilm formation of Salmonella enterica serovar Typhi

Biofilm formation is a crucial survival strategy for Salmonella enterica serovar Typhi ( S. Typhi), enabling it to withstand adverse environmental conditions and host immune responses. This process is tightly regulated by complex genetic networks. The type VI secretion system (T6SS) is an essential virulence apparatus in S. Typhi that has recently been confirmed to be functional; however, its role in biofilm formation remains poorly understood. In this study, we demonstrated that the T6SS-associated genes sciG and sciS enhanced bacterial biofilm formation and exerted similar effects under microaerophilic conditions, in SOB medium, and in the presence of ciprofloxacin. In biofilms, deletion of sciG or sciS caused collapse of the bacterial membrane and reduced bacterial viability. Transcriptomic analysis of biofilms revealed that T6SS-deficient mutants exhibited lower expression of genes associated with ribosomal function, alongside higher expression of genes involved in flagellar assembly, bacterial chemotaxis, exopolysaccharide biosynthesis, and two-component systems. Production of Vi capsular polysaccharide and expression of biofilm-associated genes were altered in the sciG or sciS mutants. sciG and sciS may function via distinct mechanisms in biofilms. These findings suggested that sciG and sciS contribute to S . Typhi biofilm formation through multiple mechanisms, possibly involving bacterial structural integrity, biofilm component production, and global transcriptional changes related to translation, energy metabolism, and signal transduction. This study provides novel insights into the mechanisms underlying chronic S . Typhi infections and may inform the development of biofilm-targeted therapeutic strategies.