Expression of the Fis protein is sustained in late-exponential- and stationary-phase cultures of Salmonella enterica serovar Typhimurium grown in the absence of aeration

• Published in: Molecular microbiology Vol. 66; no. 1; pp. 237 - 251
• Main Authors: Cróinín, Tadhg Ó, Dorman, Charles J
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.10.2007; Blackwell Publishing Ltd; Blackwell Science
• Subjects: Animals; Bacterial Proteins - biosynthesis; Bacterial Proteins - genetics; Bacteriology; Biological and medical sciences; Blotting, Western; Caco-2 Cells; Cells; CHO Cells; Cricetinae; Cricetulus; E coli; Epithelial Cells - microbiology; Escherichia coli; Escherichia coli - genetics; Escherichia coli - physiology; Factor For Inversion Stimulation Protein - biosynthesis; Fundamental and applied biological sciences. Psychology; Gene Deletion; Gene expression; Gene Expression Regulation, Bacterial; Genes; Humans; Microbiology; Miscellaneous; Proteins; Reverse Transcriptase Polymerase Chain Reaction; RNA, Bacterial - biosynthesis; RNA, Messenger - biosynthesis; Salmonella; Salmonella enterica; Salmonella typhimurium - genetics; Salmonella typhimurium - pathogenicity; Salmonella typhimurium - physiology; Sigma Factor - biosynthesis; Sigma Factor - genetics; Transcription, Genetic; Bacteria; Salmonella typhimurium; Protein; Enterobacteriaceae
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/j.1365-2958.2007.05916.x

The classic expression pattern of the Fis global regulatory protein during batch culture consists of a high peak in the early logarithmic phase of growth, followed by a sharp decrease through mid-exponential growth phase until Fis is almost undetectable at the end of the exponential phase. We discovered that this pattern is contingent on the growth regime. In Salmonella enterica serovar Typhimurium cultures grown in non-aerated SPI1-inducing conditions, Fis can be detected readily in stationary phase. On the other hand, cultures grown with standard aeration showed the classic Fis expression pattern. Sustained Fis expression in non-aerated cultures was also detected in some Escherichia coli strains, but not in others. This novel pattern of Fis expression was independent of sequence differences in the fis promoter regions of Salmonella and E. coli. Instead, a clear negative correlation between the expression of the Fis protein and of the stress-and-stationary-phase sigma factor RpoS was observed in a variety of strains. An rpoS mutant displayed elevated levels of Fis and had a higher frequency of epithelial cell invasion under these growth conditions. We discuss a model whereby Fis and RpoS levels vary in response to environmental signals allowing the expression and repression of SPI1 invasion genes.