Absence of Curli in Soil-Persistent Escherichia coli Is Mediated by a C-di-GMP Signaling Defect and Suggests Evidence of Biofilm-Independent Niche Specialization

Abstract

Escherichia coli is commonly viewed as a gastrointestinal commensal or pathogen although an increasing body of evidence suggests that it can persist in non-host environments as well. Curli are a major component of biofilm in many enteric bacteria including E. coli and are important for adherence to different biotic and abiotic surfaces. In this study we investigated curli production in a unique collection of soil-persistent E. coli isolates and examined the role of curli formation in environmental persistence. Although most soil-persistent E. coli were curli-positive, 10% of isolates were curli-negative (17 out of 170). Curli-producing E. coli (COB583, COB585, and BW25113) displayed significantly more attachment to quartz sand than the curli-negative strains. Long-term soil survival experiments indicated that curli production was not required for long-term survival in live soil (over 110 days), as a curli-negative mutant BW25113ΔcsgB had similar survival compared to wild type BW25113. Mutations in two genes associated with c-di-GMP metabolism, dgcE and pdeR, correlated with loss of curli in eight soil-persistent strains, although this did not significantly impair their survival in soil compared to curli-positive strains. Overall, the data indicate that curli-deficient and biofilm-defective strains, that also have a defect in attachment to quartz sand, are able to reside in soil for long periods of time thus pointing to the possibility that niches may exist in the soil that can support long-term survival independently of biofilm formation.

<p>A Comparative Study of Fluoroquinolone-Resistant Escherichia coli Lineages Portrays Indistinguishable Pathogenicity- and Survivability-Associated Phenotypic Characteristics Between ST1193 and ST131</p>

“…Curli promotes biofilm adhesion to abiotic surfaces or cells and contributes to persistence in hosts. 30 Cellulose promotes delayed bacterial clearance. 31 We found that the majority of E. coli ST1193 and ST131 possessed no curli/no cellulose in this study.…”

Transmission of Salmonella in Humans and Animals and its Epidemiological Factors

“…Typhimurium and S. Senftenberg adhere efficiently to fruits and vegetables, while others like S. Arizona, S. Agona and S. Heidelberg do not attach well to fruits and vegetables [50,51]. of Salmonella [55][56][57]. Biofilms are formed by cellular matrix which has been consistently found to be created by curli and cellulose [58].…”