Biology subjects

Barak, J. D.

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

5 recordsLinked to original sources

bioRxiv2026

Time, Not fungicide treatment, influences the resistome of the turf phyllosphere

Antibiotic resistance genes (ARGs) are an emerging class of environmental contaminants with significant implications for public health. Previous studies have linked fungicide exposure to elevated levels of ARGs in soil microbiomes, but research investigating the impacts of fungicide on ARGs within phyllosphere bacterial communities is limited. To address this, creeping bentgrass was treated with the fungicide active ingredients chlorothalonil, fluxapyroxad, and propiconazole and sampled at 4 hours, 96 hours, and one week post-application. Quantitative PCR (qPCR) was performed to quantify the abundance of ARGs and a metal resistance genes (MRG) abundance relative to 16s. Additionally, 16S rRNA gene sequencing was performed to characterize bacterial community composition. Results indicated that fungicide treatments did not significantly alter the relative abundance of ARGs or an MRG within bent grass bacterial communities. However, significant changes were observed over time, with changes in ARG and MRG abundance mirroring temporal shifts in bacterial beta diversity. ARGs and the MRG relative abundance had significant correlations with Proteobacteria, Actinobacteria, Bacteriadota, and Firmicutes, including with genera Pseudoxanthomas, and Dyandobacter, which contain opportunistic human pathogens. This study demonstrates that fungicides have limited influence on the abundance of ARGs and MRGs in the phyllosphere and helps guide further investigations aiming to mitigate the spread of antibiotic resistance. ImportanceAntibiotic resistance makes it harder to treat bacterial infections. Recent evidence suggests that fungicides may increase the abundance of antibiotic resistance genes (ARGs) in soil. Leaves are also treated with fungicides, but it is unclear if there will be increases of antibiotic resistance in this environment because bacteria on leaves face different physiological stresses. Additionally, plants may serve as a route of infection to humans or animals with antibiotic resistant bacteria making it a critical micro-environment to investigate. The purpose of this study was to determine whether the prevalence of antibiotic resistance on plant surfaces changes after short-term exposure to fungicides. This study shows that over short-term application periods, time has a greater effect on the abundance of genes that cause antibiotic resistance than treatment with the fungicides chlorothalonil, fluxapyroxad, and propiconazole on plants. This work helps inform future efforts to mitigate the spread of antibiotic resistance.

microbiology↗

bioRxiv2024

Established Pseudomonas syringae pv. tomato infection disrupts immigration of leaf surface bacteria to the apoplast

Bacterial disease alters the infection court creating new niches. The apoplast is an oasis from the hardships of the leaf surface and is generally inaccessible to nonpathogenic members of the phyllosphere bacterial community. Previously, we demonstrated that Salmonella enterica immigrants to the leaf surface can both enter the apoplast and replicate due to conditions created by an established Xanthomonas hortorum pv. gardneri (Xhg) infection. Here, we have expanded our investigation of how infection changes the host by examining the effects of another water-soaking pathogen, Pseudomonas syringae pv tomato (Pst), on immigrating bacteria. We discovered that, despite causing macroscopically similar symptoms as Xhg, Pst infection disrupts S. enterica colonization of the apoplast. To determine if these effects were broadly applicable to phyllosphere bacteria, we examined the fates of immigrant Xhg and Pst arriving on an infected leaf. We found that this effect is not specific to S. enterica, but that immigrating Xhg or Pst also struggled to fully join the infecting Pst population established in the apoplast. To identify the mechanisms underlying these results, we quantified macroscopic infection symptoms, examined stomata as a pinch point of bacterial entry, and characterized aspects of interbacterial competition. While it may be considered common knowledge that hosts are fundamentally altered following infection, the mechanisms that drive these changes remain poorly understood. Here, we investigated these pathogens to reach a deeper understanding of how infection alters a host from a rarely accessible, inhabitable environment to an obtainable, habitable niche. IMPORTANCEPathogens dramatically alter the host during infection. Changes in host physical and biochemical characteristics benefit the pathogen and can reshape the composition of the bacterial community. In fact, rare members of the plant microbiota, namely bacterial human pathogens, such as Salmonella enterica, thrive in some plant infection courts. The increased success of human pathogens results from the conversion of the rarely accessible, inhabitable apoplast to an obtainable, habitable niche following infection. Here, we compared two phytopathogens, Pseudomonas syringae pv. tomato and Xanthomonas hortorum pv. gardneri within a tomato host and uncovered relevant niche changes potentially overlooked by the similarity in macroscopic symptoms. We investigated mechanisms used to reshape the host environment to the pathogens benefit and either success or failure of newly arriving immigrant bacteria. This study reveals information about bacterial disease of leaves and key changes that remodel inhospitable niches to new, conducive environments in the diseased host.

microbiology↗

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↗