Vertical variation of E. coli O157:H7 survival in a black soil column under freeze-thaw cycles conditions

In this study, the survival of E. coli O157:H7 (EcO157) in the vertical layers of a black soil column under FTCs conditions was investigated. The survival parameters including ttd (time needed to reach detection limit), p (shape parameter) and δ (time needed to first decimal reduction) were obtained. Compared with non-FTCs control, FTCs resulted in a rapid decline in EcO157 cell counts across all vertical soil layers, and a greater ttd tended to correspond to a deeper vertical layer. FTCs increased soil NO₃⁻-N, NH₄⁺-N, and neutral phosphatase activity (P < 0.01), and decreased soil moisture content, available phosphorus (AP), and microbial biomass carbon in vertical soil layers in comparison with non-FTCs control. The results of the coexistence network analysis and Mantel test showed that soil physicochemical properties, enzyme activities, and bacterial communities correlated (P < 0.05) with the survival of EcO157. Structural equation model further revealed that AP and bacterial communities directly and positively related to EcO157 survival (P < 0.01). NO₃⁻-N directly and negatively correlated ttd (P < 0.01), and indirectly influenced ttd via shifting the structure and composition of bacterial communities. In summary, our results revealed the survival profiles of EcO157 in vertical soil layers under FTCs, and provided additional insights into the mechanisms of bacterial pathogens survival in seasonally frozen soils.