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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Produce Safety and Microbiology Research » Research » Publications at this Location » Publication #322553
Title: The polymorphic aggregative phenotype of Shiga toxin-producing Escherichia coli O111 depends on rpoS and curli

Author
item Diodati, Michelle
item Bates, Anne
item Miller, William - Bill
item Carter, Michelle
item Zhou, Yaguang
item Brandl, Maria

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2015
Publication Date: 12/18/2016
Citation: Diodati, M.E., Bates, A.H., Miller, W.G., Carter, M.Q., Zhou, Y., Brandl, M. 2016. The polymorphic aggregative phenotype of Shiga toxin-producing Escherichia coli O111 depends on rpoS and curli. Applied and Environmental Microbiology. 82:1475–1485. doi: 10.1128/AEM.03935-15.

Interpretive Summary: Escherichia coli O111 is an emerging Shiga toxin-producing E. coli (STEC). It is among the six most common non-O157:H7 STEC implicated in foodborne illness and has caused several outbreaks linked to produce, such as lettuce and cabbage. We have assembled previously a collection of O111 strains that encompasses environmental isolates from an important produce-growing region of the USA and shown that theses isolates and outbreak strains, but not sporadic case strains, share a strong aggregative phenotype. We report here the isolation of naturally non-aggregative variants of environmental and outbreak strains that lack curli fimbriae production and RpoS function. Deletion of curli and rpoS genes in an aggregative outbreak strain abolished cluster formation, which was rescued when curli biogenesis or RpoS function, respectively, was restored. Complementation of a naturally non-aggregative variant with RpoS also conferred curli production and aggregation. Immunomicroscopy with fluorescently labeled anti-curli antibody revealed that the fimbriae were undetectable on the cells of the non-aggregative variant and the RpoS mutant, but present in large quantities in the intercellular matrix of the assemblages formed by aggregative strains. Sequence analysis of rpoS in the aggregative strain and its variant showed a single substitution of asparagine for threonine at aa124. Our results indicate that the multicellular behavior of STEC O111 is RpoS-dependent via positive regulation of curli production. Aggregation may confer a fitness advantage in O111 strains under stressful conditions in hydrodynamic environments along the food production chain, while the occurrence of non-aggregative variants may allow for the cell population to adapt to conditions benefiting a planktonic life style.

Technical Abstract: Escherichia coli O111 is an emerging non-O157:H7 Shiga toxin-producing E. coli (STEC). We previously reported that outbreak and environmental, but not sporadic case, strains of STEC O111 share a distinct aggregation phenotype (M. E. Diodati, A. H. Bates, M. B. Cooley, S. Walker, R. E. Mandrell, and M. T. Brandl, Foodborne Pathog. Dis. 2015, 12: 235-243, doi:10.1089/fpd.2014.1887). We show here, the natural occurrence of non-aggregative variants in single STEC O111 strains. These variants do not produce curli fimbriae, lack RpoS function, but synthesize cellulose. Deletion of csgBAC or rpoS in an aggregative outbreak strain abolished aggregate formation, which was rescued when curli biogenesis or RpoS function, respectively, was restored. Complementation of a non-aggregative variant with RpoS also conferred curli production and aggregation. These observations were supported by Western blot analysis with an anti-O111 CsgBA antibody. Immunomicroscopy revealed that curli was undetectable on the cells of the non-aggregative variant and the RpoS mutant, but present in large quantities in the intercellular matrix of the assemblages formed by aggregative strains. Sequence analysis of rpoS in the aggregative strain and its variant showed a single substitution of asparagine for threonine at aa124. Our results indicate that the multicellular behavior of STEC O111 is RpoS-dependent via positive regulation of curli production. Aggregation may confer a fitness advantage in O111 strains under stressful conditions in hydrodynamic environments along the food production chain, while the occurrence of non-aggregative variants may allow for the cell population to adapt to conditions benefiting a planktonic life style.