Interactions of Salmonella enterica Serovar Typhimurium and Pectobacterium carotovorum within a tomato soft rot

Authors: GEORGE, ANDREE - University Of Florida; COX, CLAYTON E - Former ARS Employee; DESAI, PRERAK - University Of California; PORWOLIK, STEFFEN - University Of California; CHU, WEIPING - University Of California; DE MORAES, MARCOS - University Of Florida; MCCLELLAND, MICHAEL - University Of California; Brandl, Maria; TEPLITSKI, MAX - University Of Florida

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2017
Publication Date: 12/15/2017
Citation: George, A., Cox, C., Desai, P., Porwolik, S., Chu, W., De Moraes, M.H., McClelland, M., Brandl, M., Teplitski, M. 2017. Interactions of Salmonella enterica Serovar Typhimurium and Pectobacterium carotovorum within a tomato soft rot. Applied and Environmental Microbiology. 84:e01913-17. https://doi.org/10.1128/AEM.01913-17.
DOI: https://doi.org/10.1128/AEM.01913-17

Interpretive Summary: Outbreaks of gastroenteritis linked to fruits and vegetables continue to be a food safety concern. Earlier studies demonstrated that the presence of phytopathogens in supermarket produce was a significant risk factor associated with increased Salmonella carriage. This study aimed to uncover the mechanisms that enable Salmonella Typhimurium to benefit from the degradation of plant tissue by the soft-rot plant pathogen Pectobacterium carotovorum. The hypothesis that the liberation of starch by Pectobacterium makes this polymer available to Salmonella, thus allowing it to colonize degraded tomato tissue was tested first and proven null. To identify the functions involved in Salmonella soft rot colonization, we carried out transposon insertion sequencing coupled with the phenotypic characterization of the mutants. The results indicate that Salmonella pathways necessary for nucleic acid synthesis, amino acid synthesis, and motility are contributors to the persistence of Salmonella in soft rots. These results define global mechanisms of interactions between Salmonella and host bacteria, and the conditions that allow Salmonella to establish within alternate hosts.

Technical Abstract: The human pathogen Salmonella has shown a remarkable adaptability which allows these bacteria to thrive in a variety of environments and hosts. The manner in which these pathogens establish within a niche amidst the native microbiota remains poorly understood. Here, we aimed to uncover the mechanisms that enable Salmonella Typhimurium to benefit from the degradation of plant tissue by the soft-rot plant pathogen Pectobacterium carotovorum. The hypothesis that the liberation of starch by Pectobacterium (not utilized by this soft-rotter) makes this polymer available to Salmonella, thus allowing it to colonize soft rots was tested first and proven null. To identify the functions involved in the Salmonella soft rot colonization, we carried out transposon insertion sequencing coupled with the phenotypic characterization of the mutants. The data indicate that Salmonella experiences a metabolic shift in response to the changes in the environment brought on by Pectobacterium and likely coordinated by the csrBC small regulator RNA. While csrBC and flhD prove to be of importance in the soft rot, the global two-component system encoded by barA/sirA (which controls csrBC and flhDC under laboratory conditions) does not appear to be necessary for the observed phenotype. Motility, and synthesis of nucleic and amino acids, play critical roles in the growth of Salmonella in the soft rot.