Vertical variation in Salmonella Typhimurium survival in black soil under freezing-thawing cycles: Roles of soil properties, microbial communities, and enzyme activities

Freezing-thawing cycles (FTCs) have been demonstrated to significantly change soil properties, however, such changes of soil properties in response to survival of bacterial pathogens are not well documented. In this study, we used laboratory column experiments to investigate the vertical variations of soil physicochemical properties, bacterial communities and enzyme activities under FTCs conditions, and their effects on the survival of Salmonella Typhimurium ( S. Typhimurium). The survival parameters ( ttd, δ , and p ) were obtained by fitting the data to the Weibull model. The results showed that the FTCs treatment (15 cycles) significantly decreased the ttd in comparison to non-FTCs (control). S. Typhimurium tend to survive longer ( P <0.05) as soil depth increased. Multivariate analysis revealed that the vertical variation of survival of S. Typhimurium was strongly correlated to soil properties ( P <0.05), bacterial communities, and soil enzyme activities ( P <0.05). Pearson correlation analysis, Mantel tests and co-occurrence network analysis collectively showed that pH, available phosphorus (AP), NH 4 + -N, urease (URE) activity, sand content, and relative abundances of Actinobacteria, Proteobacteria, Gemmatimonadetes , and Bacteroidetes were correlated with the survival of S. Typhimurium ( P <0.05). The structural equation model indicated that soil properties directly and indirectly influenced the survival of S . Typhimurium by shifting bacterial communities. Our results highlighted the vertical variation of survival behavior of S . Typhimurium in soils subjected to FTCs, and the data could be useful to evaluate the health risks associated with this pathogen.