Time of arrival during disease progression and humidity additively influence Salmonella enterica colonization of lettuce

The interplay between plant host, phytopathogenic bacteria, and enteric human pathogens in the phyllosphere have consequences for human health. Salmonella enterica has been known to take advantage of phytobacterial infection to increase its success on plants, but there is little knowledge of additional factors that may influence the relationship between enteric pathogen and plant disease. In this study, we investigated the role of humidity and the extent of plant disease progression on S. enterica colonization of plants. We found that high humidity was necessary for replication of S. enterica on diseased lettuce, but not required for S. enterica ingress into the UV-protected apoplast. Additionally, the Xanthomonas hortorum pv. vitians (hereafter, X. vitians) - infected lettuce host was found to be a relatively hostile environment for S. enterica when it arrived prior to the development of watersoaking or following necrosis onset, supporting the existence of an ideal window during X. vitians infection progress that maximizes S. enterica survival. In vitro growth studies in sucrose media suggest that X. vitians may allow S. enterica to benefit from cross-feeding during plant infection. Overall, this study emphasizes the role of phytobacterial disease as a driver of S. enterica success in the phyllosphere, demonstrates how time of arrival during disease progress can influence S. entericas fate in the apoplast, and highlights the potential for humidity to transform an infected apoplast into a growth-promoting environment for bacterial colonizers. ImportanceBacterial leaf spot of lettuce caused by X. vitians is a common threat to leafy green production. The global impact caused by phytopathogens, including X. vitians, is likely to increase with climate change. We found that even under a scenario where increased humidity did not enhance plant disease, high humidity had a substantial effect on facilitating S. enterica growth on Xanthomonas-infected plants. High humidity climates may directly contribute to the survival of human enteric pathogens in crop fields or indirectly affect bacterial survival via changes to the phyllosphere brought on by phytopathogen disease.