AUTHOR=Lovelace Amelia H. , Chen Hsiao-Chun , Lee Sangwook , Soufi Ziad , Bota Pedro , Preston Gail M. , Kvitko Brian H. 

TITLE=RpoS contributes in a host-dependent manner to Salmonella colonization of the leaf apoplast during plant disease

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.999183

DOI=10.3389/fmicb.2022.999183

ISSN=1664-302X

ABSTRACT=<p>Contaminated fresh produce has been routinely linked to outbreaks of Salmonellosis. Multiple studies have identified <italic>Salmonella enterica</italic> factors associated with successful colonization of diverse plant niches and tissues. It has also been well documented that <italic>S. enterica</italic> can benefit from the conditions generated during plant disease by host-compatible plant pathogens. In this study, we compared the capacity of two common <italic>S. enterica</italic> research strains, 14028s and LT2 (strain DM10000) to opportunistically colonize the leaf apoplast of two model plant hosts <italic>Arabidopsis thaliana</italic> and <italic>Nicotiana benthamiana</italic> during disease. While <italic>S. enterica</italic> 14028s benefited from co-colonization with plant-pathogenic <italic>Pseudomonas syringae</italic> in both plant hosts, <italic>S. enterica</italic> LT2 was unable to benefit from <italic>Pto</italic> co-colonization in <italic>N. benthamiana</italic>. Counterintuitively, LT2 grew more rapidly in <italic>ex planta N. benthamiana</italic> apoplastic wash fluid with a distinctly pronounced biphasic growth curve in comparison with 14028s. Using allelic exchange, we demonstrated that both the <italic>N. benthamiana</italic> infection-depedent colonization and apoplastic wash fluid growth phenotypes of LT2 were associated with mutations in the <italic>S. enterica rpoS</italic> stress-response sigma factor gene. Mutations of <italic>S. enterica rpoS</italic> have been previously shown to decrease tolerance to oxidative stress and alter metabolic regulation. We identified <italic>rpoS-</italic>dependent alterations in the utilization of L-malic acid, an abundant carbon source in <italic>N. benthamiana</italic> apoplastic wash fluid. We also present data consistent with higher relative basal reactive oxygen species (ROS) in <italic>N. benthamiana</italic> leaves than in <italic>A. thaliana</italic> leaves. The differences in basal ROS may explain the host-dependent disease co-colonization defect of the <italic>rpoS</italic>-mutated LT2 strain. Our results indicate that the conducive environment generated by pathogen modulation of the apoplast niche can vary from hosts to host even with a common disease-compatible pathogen.</p>