Biology subjects

Barak, J. D.

Publications and source records attributed to Barak, J. D..

3 recordsLinked to original sources

bioRxiv2024

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.

microbiology↗

bioRxiv2023

Narrow, but not broad, spectrum resistance and disease reshape phyllosphere bacterial communities

The phyllosphere is a restrictive environment for microbes, resulting in microbial communities typically dominated by select taxa with specific adaptations for success in this niche. However, biotic stress, especially from plant disease, could disrupt this environment in ways that alter the resulting phyllosphere community, with potential consequences for plant and human health. Additionally, plant disease resistance, through both broad (pattern-triggered immunity) and specific (effector-triggered immunity) resistance, could affect non-pathogenic communities directly or indirectly via effects on disease progression. Here, we tested how transgenic ETI and PTI resistance genes affected the phyllosphere communities of tomato plants in the face of infection by Xanthomonas perforans and the resulting bacterial spot disease. We found that the expression of the Bs2 transgene (ETI) had major effects on phyllosphere communities, while the EFR (PTI) transgene did not. The effect of the Bs2 resistance gene could be largely attributed to the change in disease symptoms. Diseased leaves harbored reduced bacterial diversity and reductions in major phyllosphere inhabitants (e.g. Sphinogmonas and Methylobacterium), while a limited number of bacterial genera showed increased relative abundance on diseased leaves. These results suggest that phyllosphere communities are sensitive to the direct and indirect effects of plant disease and resistance, and the consequences of these shifts for plant and human health deserve further investigation.

plant biology↗

bioRxiv2022

Xanthomonas infection transforms the apoplast into an accessible and habitable niche for Salmonella enterica

The physiology of plant hosts can be dramatically altered by phytopathogens. Xanthomonas hortorum pv. gardneri is one such pathogen that creates an aqueous niche within the leaf apoplast by manipulating the plant via the transcription activator-like effector AvrHah1. Simultaneous immigration of X. gardneri and Salmonella enterica to healthy tomato leaves results in increased survival of S. enterica as Xanthomonas infection progresses. However, the fate of S. enterica following arrival on actively infected leaves has not been examined. We hypothesized that the water-soaking caused by X. gardneri could facilitate the ingression of S. enterica into the apoplast, and that this environment would be conducive for growth. We found that a water-soaked apoplast, abiotically or Xanthomonas-infected, enabled surface S. enterica to passively localize to the protective apoplast and facilitated migration of S. enterica to distal sites within the aqueous apoplast. AvrHah1 contributed to the protection and migration of S. enterica early in X. gardneri infection. Xanthomonas-infected apoplasts facilitated prolonged survival and promoted S. enterica replication compared to healthy apoplasts. Access to an aqueous apoplast in general protects S. enterica from immediate exposure to irradiation whereas, the altered environment created by Xanthomonas infection provides growth-conducive conditions for S. enterica. Overall, we have characterized an ecological relationship in which host infection converts an unreachable niche to a habitable environment. ImportanceBacterial spot disease caused by Xanthomonas species devastates tomato production worldwide. Salmonellosis outbreaks from consumption of raw produce have been linked to the arrival of Salmonella enterica on crop plants in the field via contaminated irrigation water. Considering that Xanthomonas is difficult to eradicate, it is highly likely that S. enterica arrives on leaves pre-colonized by Xanthomonas with infection underway. Our study demonstrates that infection and disease fundamentally alter the leaf, resulting in redistribution and change in abundance of a phyllosphere bacterial member. These findings contribute to our understanding of how S. enterica manages to persist on leaf tissue despite lacking the ability to liberate nutrients from plant cells. More broadly, this study reveals a mechanism by which physiochemical changes to a host environment imposed by a plant pathogen can convert an uninhabitable leaf environment into a hospitable niche for select epiphytic microbes.

microbiology↗