Soil pH and microbial diversity constrain the survival of E. coli in soil

Abstract

The presence of Eschericia coli (E. coli) leads to potential outbreaks of disease, demonstrating the importance of understanding how such organisms survive in secondary environments such as soil. Biotic and abiotic soil characteristics play a role in E. coli survival, but it remains unclear how these two aspects interact with survival and whether it is linked to toxin genes. Here we evaluated the survival of three E. coli O157:H7strains: Shiga toxin-producing E. coli, its mutant without stx genes and strain without virulence genes in 4 distinct Chinese soils. To further disentangle the effects of microbial diversity, soils were manipulated to generate a gradient of microbial diversity (10−1, 10−6, and a sterile soil [γ-irradiated control]). Overall, our results showed the E. coli O157:H7 survival time decreased in all treatments, ranging from 8.23 ± 5.42 to 62.33 ± 35.80 days. The fastest decline was with the Shiga toxin-producing strain at 10−1 dilution, whereas the strain without virulence genes, persisted the longest 178 days in the γ sterilized control. These results confirmed the importance of biodiversity upon E. coli invasion and revealed virulence genes negatively influenced survival. The negative correlation between community niche or niche breadth of soil communities and survival, indicated that resource competition also was the major driver of E. coli O157:H7 survival. Moreover, path analyses revealed that soil pH exerted a critical role on the persistence of E. coli O157:H7, higher pH values produced longer survival time in each strain. These conclusions are of relevance for agricultural situations, where anthropogenic influences lead to decreased soil diversity, increased soil pH and resource input through manure application, which can potentially increase the survival time of E. coli O157:H7, the expanding the window of opportunity for food contamination.