Sulfate import inSalmonellaTyphimurium impacts bacterial aggregation and the neutrophil respiratory burst

During enteric salmonellosis, neutrophil generated reactive oxygen species alter the gut microenvironment favoring survival ofSalmonellaTyphimurium. While the type-3 secretion system-1 (T3SS-1) and flagellar motility are potentSalmonellaTyphimurium agonists of the neutrophil respiratory burstin vitro, neither of these pathways alone are responsible for stimulation of a maximal respiratory burst. In order to identifySalmonellaTyphimurium genes that impact the magnitude of the neutrophil respiratory burst, we performed a two-step screen of defined mutant libraries in co-culture with neutrophils. We first screenedSalmonellaTyphimurium mutants lacking defined genomic regions, followed by the individual mutants mapping to genomic regions under selection. Mutants in four genes,STM1696(sapF),STM2201(yeiE),STM2112(wcaD), andSTM2441(cysA), induced an attenuated respiratory burst. We linked the altered respiratory burst to reduced T3SS-1 expression and/or altered flagellar motility for two mutants (ΔSTM1696and ΔSTM2201). The ΔSTM2441mutant, defective for sulfate transport, formed aggregates in minimal media and adhered to surfaces in rich media, suggesting a role for sulfur homeostasis in regulation of aggregation/adherence. We linked the aggregation/adherence phenotype of the ΔSTM2441mutant to biofilm-associated protein A and flagellins and hypothesize that aggregation caused the observed reduction in the magnitude of the neutrophil respiratory burst. Our data demonstrate thatSalmonellaTyphimurium has numerous mechanisms to limit the magnitude of the neutrophil respiratory burst. These data further inform our understanding of how Salmonellamay alter neutrophil antimicrobial defenses.