Salmonella Typhimurium encoded cold shock protein E is essential for motility and biofilm formation
Semanti Ray, Rochelle Da Costa, Samriddhi Thakur, Dipankar Nandi
Abstract
The ability of bacteria to form biofilms increases their survival under adverse environmental conditions. Biofilms have enormous medical and environmental impact; consequently, the factors that influence biofilm formation are an important area of study. In this investigation, the roles of two cold shock proteins (CSP) during biofilm formation were investigated in Salmonella Typhimurium, which is a major foodborne pathogen. Among all CSP transcripts studied, the expression of cspE (STM14_0732) was higher during biofilm growth. The cspE deletion strain (Δ cspE ) did not form biofilms on a cholesterol coated glass surface; however, complementation with WT cspE , but not the F30V mutant, was able to rescue this phenotype. Transcript levels of other CSPs demonstrated up-regulation of cspA (STM14_4399) in Δ cspE . The cspA deletion strain (Δ cspA ) did not affect biofilm formation; however, Δ cspE Δ cspA exhibited higher biofilm formation compared to Δ cspE . Most likely, the higher cspA amounts in Δ cspE reduced biofilm formation, which was corroborated using cspA over-expression studies. Further functional studies revealed that Δ cspE and Δ cspE Δ cspA exhibited slow swimming but no swarming motility. Although cspA over-expression did not affect motility, cspE complementation restored the swarming motility of Δ cspE . The transcript levels of the major genes involved in motility in Δ cspE demonstrated lower expression of the class III ( fliC , motA , cheY ), but not class I ( flhD ) or class II ( fliA , fliL ), flagellar regulon genes. Overall, this study has identified the interplay of two CSPs in regulating two biological processes: CspE is essential for motility in a CspA-independent manner whereas biofilm formation is CspA-dependent.