|Andreozzi, Elisa - University Of Calabria|
|Nguyen, Ly Huong|
Submitted to: Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/9/2017
Publication Date: 4/1/2017
Citation: Uhlich, G.A., Chen, C., Cottrell, B.J., Andreozzi, E., Irwin, P.L., Nguyen, L.T. 2017. Gene duplication and promoter mutation expand the range csgD-dependent biofilm responses in a STEC population. Microbiology. 163:611-621.
Interpretive Summary: The ability to form biofilms, bacteria existing as tightly packed communities encased in a self-secreted protein and polysaccharide matrix, allows food-borne pathogens to resist environmental stresses, antimicrobials, and antibiotics. However, biofilms can be either advantageous or detrimental, depending on the specific environment encountered. Therefore, Shiga toxin-producing E. coli (STEC) has developed a sophisticated network focused on the key regulatory gene, csgD, to control biofilm expression. Using whole genome and RNA sequencing, we investigated biofilm regulation using a STEC strain containing a csgD mutation that confers strong biofilm formation at all times. Our results have identified structural and regulatory genes important for strong biofilm formation. We also discovered a chromosomal duplication of a csgD-suppressor gene that caused delayed entry into the biofilm state. This mechanism may provide a new target for designing intervention strategies to control STEC in food.
Technical Abstract: Expression of Escherichia coli major biofilm components, curli fimbriae and cellulose, require the CsgD transcription factor. A complex regulatory network allows environmental control of csgD transcription and biofilm formation. However, most clinical serotype O157:H7 strains contain prophage insertions in the csgD regulator, mlrA, or mutations in other regulators that restrict csgD expression. These barriers can be circumvented by certain compensating mutations that restore higher csgD expression. One mechanism is via csgD promoter mutations that switch sigma factor utilization. Biofilm-forming variants utilizing rpoD rather than rpoS have been identified in glycerol freezer stocks of the non-biofilm-forming foodborne outbreak strain, ATCC 43894. In this study we used WGS and RNA-seq to study genotypic, phenotypic and transcriptomic differences between those strains. In addition to defining the consequences of the csgD promoter switch and identifying new csgD-controlled genes, we discovered a genome duplication in the 43894 parent strain that tightened csgD regulation.