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Despite the clinical relevance of major tuberculous pathogens to domestic animals and humans, the understanding of mycobacterial transmission modes, pathways, and interactions in their natural habitats remains very limited. The reason for this is primarily because ecological and evolutionary concepts have not yet been widely applied to the understanding of these bacteria. Most existing research on mycobacterial transmission is not founded on hypothesis testing but rather tends to accept the most recent explanation and turn it into a canonical fact. In this comparative review, we discuss plausible alternative hypotheses against a null hypothesis of environmental origin to intensify research on mycobacterial pathogens and their capacity to spread in the context of global change. We highlight a major bias in perceptions of mycobacterial infection transmission, with most work concentrating only on the contagious stage of tuberculous clones. We suggest broadening the field to include research on environmental non-tuberculous mycobacteria and their life histories. A deeper understanding of mycobacterial ecology and evolution is more important now than ever, considering the vast diversity of known and unknown mycobacterial species in natural ecosystems. Infectious disease medicine, veterinary science, and public health surveillance should take a more integrative disease ecology approach to enhance the development of new approaches for control of these animal and human pathogens. 

Abstract PremiseEndophytic plant‐microbe interactions range from mutualistic relationships that confer important ecological and agricultural traits to neutral or quasi‐parasitic relationships. In contrast to root‐associated endophytes, the role of environmental and host‐related factors in the acquisition of leaf endophyte communities at broad spatial and phylogenetic scales remains sparsely studied. We assessed endofoliar diversity to test the hypothesis that membership in these microbial communities is driven primarily by abiotic environment and host phylogeny. MethodsWe used a broad geographic coverage of North America in the genusHeucheraL. (Saxifragaceae), representing 32 species and varieties across 161 populations. Bacterial and fungal communities were characterized using 16S and ITS amplicon sequencing, respectively, and standard diversity metrics were calculated. We assembled environmental predictors for microbial diversity at collection sites, including latitude, elevation, temperature, precipitation, and soil parameters. ResultsAssembly patterns differed between bacterial and fungal endophytes. Host phylogeny was significantly associated with bacteria, while geographic distance was the best predictor of fungal community composition. Species richness and phylogenetic diversity were consistent across sites and species, with only fungi showing a response to aridity and precipitation for some metrics. Unlike what has been observed with root‐associated microbial communities, in this system microbes show no relationship with pH or other soil factors. ConclusionsOverall, this work improves our understanding of the large‐scale patterns of diversity and community composition in leaf endophytes and highlights the relative significance of environmental and host‐related factors in driving different microbial communities within the leaf microbiome. 

ABSTRACT Mycobacterium ulceranspseudoshottsiiis a mycolactone‐producing bacterium previously isolated from Striped Bass (Morone saxatilis(Walbaum)) from Chesapeake Bay and adjacent waters of the Atlantic Coast of North America. We report the first molecular detection of this pathogen in the native Gulf strain ofMorone saxatiliscollected from the Pearl River, Mississippi (USA). Molecular identification was conducted using a novel PCR assay targeting the parA‐625 intergenic spacer of the virulence‐associated pMUM plasmid. The isolate was unambiguously assigned toM. u. pseudoshottsiibased on diagnostic single nucleotide polymorphisms (SNPs) and phylogenetic analysis. This report expands the known range ofM. u. pseudoshottsiito include Gulf Coast watersheds and highlights the need for enhanced surveillance in wild and aquacultured fish populations of the southern United States. 

Mycolactone is a cytotoxic lipid metabolite produced byMycobacterium ulcerans, the environmental pathogen responsible for Buruli ulcer, a neglected tropical disease.Mycobacterium ulceransis prevalent in West Africa, particularly found in lentic environments, where mosquitoes also occur. Researchers hypothesize mosquitoes could serve as a transmission mechanism resulting in infection byM.ulceranswhen mosquitoes pierce skin contaminated withM.ulcerans. The interplay between the pathogen, mycolactone, and mosquito is only just beginning to be explored. A triple-choice assay was conducted to determine the host-seeking preference ofAedes aegyptibetweenM.ulceranswildtype (MU, mycolactone active) and mutant (MU^lac-, mycolactone inactive). Both qualitative and quantitative differences in volatile organic compounds’ (VOCs) profiles of MU and MU^lac-were determined by GC-MS. Additionally, we evaluated the interplay betweenAe.aegyptiproximity andM.ulceransmRNA expression. The results showed that mosquito attraction was significantly greater (126.0%) to an artificial host treated with MU than MU^lac-. We found that MU and MU^lacproduced differential profiles of VOCs associated with a wide range of biological importance from quorum sensing (QS) to human odor components. RT-qPCR assays showed that mycolactone upregulation was 24-fold greater for MU exposed toAe.aegyptiin direct proximity. Transcriptome data indicated significant induction of ten chromosomal genes of MU involved in stress responses and membrane protein, compared to MU^lac-when directly having access to or in near mosquito proximity. Our study provides evidence of possible interkingdom interactions between unicellular and multicellular species that MU present on human skin is capable of interreacting with unrelated species (i.e., mosquitoes), altering its gene expression when mosquitoes are in direct contact or proximity, potentially impacting the production of its VOCs, and consequently leading to the stronger attraction of mosquitoes toward human hosts. This study elucidates interkingdom interactions between viableM.ulceransbacteria andAe.aegyptimosquitoes, which rarely have been explored in the past. Our finding opens new doors for future research in terms of disease ecology, prevalence, and pathogen dispersal outside of theM.ulceranssystem. 

ABSTRACT Understanding the interactions of ecosystems, humans and pathogens is important for disease risk estimation. This is particularly true for neglected and newly emerging diseases where modes and efficiencies of transmission leading to epidemics are not well understood. Using a model for other emerging diseases, the neglected tropical skin disease Buruli ulcer (BU), we systematically review the literature on transmission of the etiologic agent, Mycobacterium ulcerans (MU), within a One Health/EcoHealth framework and against Hill's nine criteria and Koch's postulates for making strong inference in disease systems. Using this strong inference approach, we advocate a null hypothesis for MU transmission and other understudied disease systems. The null should be tested against alternative vector or host roles in pathogen transmission to better inform disease management. We propose a re-evaluation of what is necessary to identify and confirm hosts, reservoirs and vectors associated with environmental pathogen replication, dispersal and transmission; critically review alternative environmental sources of MU that may be important for transmission, including invertebrate and vertebrate species, plants and biofilms on aquatic substrates; and conclude with placing BU within the context of other neglected and emerging infectious diseases with intricate ecological relationships that lead to disease in humans, wildlife and domestic animals.