Escherichia coli are a common copiotrophic bacteria found in the mammalian gut microbiome. The introduction of Escherichia coli to an agricultural soil, via contaminated water, compost, or raw manure, exposes the bacterium to a medley of ecological forces not found in a mammalian gut environment. This study assesses a variety of abiotic and biotic soil factors that influence the ability of an “invasive” copiotrophic coliform bacterium to survive in compost-amended agricultural soil. The study was split into field and laboratory components. In the field experiment, a cocktail of rifampicin-resistant generic E. coli strains was added to plots with the following treatments: dairy windrow compost, dairy vermicompost, poultry windrow compost, or no compost. E. coli abundance was measured over a six month field season, along with soil water potential, soil temperature, extracellular enzyme activity, microbial respiration, and PLFA, 16S, and ITS sequencing of the microbial community. In a separate lab experiment, the same cocktail was added to sterile and nonsterile extracts of eight different composts and one soil from the field sites. E. coli abundance was monitored over a one week period and composts were analyzed for their nutrient profile.
Results/Conclusions
Results of the field experiment show that soil saturation affected microbial community composition and correlated negatively with microbial extracellular enzyme activity and respiration rates. Such conditions may give invasive facultative anaerobes, such as E. coli, a competitive advantage. The lab experiment showed that E. coli were able to grow well in sterile compost extracts, without microbial competition for nutrients. Conversely, E. coli populations were only able to survive in non-sterile soil extracts. These results suggest that copiotrophic organisms adapted for high-nutrient environments may depend on the extracellular enzyme activity of native oligotrophic organisms to acquire sufficient nutrients to survive in soils. Additionally, both experiments show that E. coli has higher survival rates in soils amended with poultry compost, likely due to the high ammonium levels. Correlations between abiotic factors, community composition, and E. coli survival in this study reveal insights into the complex relationships that occur in disturbed agricultural soil environments. Further work on E. coli’s response to targeted organisms and nutrients could have implications for agricultural considerations in food safety and microbial ecology