Investigating the Role of CsgD in Salmonella Biofilm Formation and Virulence

When exposed to environmental stress, a pure culture of Salmonella enterica serovar Typhimurium (S. Typhimurium) differentiates into two specialized cell types with 34% differential gene expression: planktonic cells and multicellular aggregates, also called biofilm. Some conditions that support phenotype switching are known, but many intrinsic and extrinsic origins of signals are unknown. S. Typhimurium phenotype switching may promote transmission under variable conditions; planktonic cells express virulence factors and are immediately able to infect a new host, whereas aggregates can resist harsh environmental conditions until an opportunity to infect a new host arises. The objective of these research projects was to determine whether signals in the host gut could promote phenotype switching, and to determine the suite of genes controlled during phenotype switching, to understand this phenomenon and how it contributes to transmission. Differences in expression between biofilm aggregates and planktonic cells are directed by bistable expression of CsgD, the central biofilm regulator. CsgD is expressed at low levels in planktonic cells and at high levels in biofilm cells, and coordinates the global shift in expression . A ChIP-seq experiment was performed to identify the regulatory targets of CsgD. The technique was refined for improved antibody binding and sample consistency; however, no statistically significant regulatory regions were identified by this method. Phenotype switching could initiate in the host gut, as a result of extrinsic signals from the host or microbiota, during infection. Gene expression of virulence- or persistence- associated genes that were differentially expressed in RNA-seq data were measured by luciferase assay with promoter-luxCDABE reporter in the presence of chemostat waste effluent. The only major changes to gene expression levels or times in the presence of waste effluent may be due to additional resources for growth provided by the waste effluent and chemostat media control