Biology subjects

Kolter, R.

Publications and source records attributed to Kolter, R..

5 recordsLinked to original sources

bioRxiv2024

Complementary roles of EPS, T3SS and Expansin for virulence of Erwinia tracheiphila, the causative agent of cucurbit wilt

Erwinia tracheiphila (Smith) is a recently emerged plant pathogen that causes severe economic losses in cucurbit crops in temperate Eastern North America. E. tracheiphila is xylem restricted, and virulence is thought to be related to Exopolysaccharides (EPS) and biofilm formation, which occlude the passage of sap in xylem vessels and causes systemic wilt. However, the role of EPS and biofilm formation, and their contribution to disease in relation to other virulence loci are unknown. Here, we use deletion mutants to explore the roles of EPS, Hrp Type III secretion system (Hrp T3SS) and Expansin in plant colonization and virulence. Then, we quantify the expression of the genes encoding these factors during infection. Our results show that Exopolysaccharides are essential for E. tracheiphila survival in host plants, while Hrp T3SS and Expansin are dispensable for survival but needed for systemic wilt symptom development. EPS and Hrp T3SS display contrasting expression patterns in the plant, reflecting their relevance in different stages of the infection. Finally, we show that expression of the eps and hrpT3SS operons is downregulated in mildly increased temperatures, suggesting a link between expression of these virulence factors and geographic restriction of E. tracheiphila to temperate regions. Our work highlights how E. tracheiphila virulence is a complex trait where several loci are coordinated during infection. These results further shed light into the relationship between virulence factors and the ecology of this pathosystem, which will be essential for developing sustainable management strategies for this emerging pathogen.

microbiology↗

bioRxiv2019

The microbiomes of seven lichen genera reveal host specificity, a reduced core community and potential as source of antimicrobials

The High Andean Paramo ecosystem is a unique neotropical mountain biome considered a diversity and evolutionary hotspot. Lichens, which are complex symbiotic structures that contain diverse commensal microbial communities, are prevalent in Paramos. There they play vital roles in soil formation and mineral fixation. In this study we analyzed the microbiomes of seven lichen genera in two Colombian Paramos using 16S rRNA gene analyses and provide the first description of the bacterial communities associated with Cora and Hypotrachyna lichens. Paramo lichen microbiomes were diverse, and in some cases were distinguished based on the identity of the lichen host. The majority of the lichen-associated microorganisms were not present in all lichens sampled and could be considered transient or specialists. We also uncovered sixteen shared taxa that suggest a core lichen microbiome among this diverse group of lichens, broadening our concept of these symbiotic structures. Additionally, we identified strains producing compounds active against clinically relevant pathogens. These results indicate that lichen microbiomes from the Paramo ecosystem are diverse and host-specific but share a taxonomic core and can be a source of new bacterial taxa and antimicrobials.

microbiology↗

bioRxiv2019

A horizontally acquired expansin gene increases virulence of the emerging plant pathogen Erwinia tracheiphila

All land plants depend on proteins called expansins that non-enzymatically loosen structural cellulose, enabling cell wall extension during normal growth. Surprisingly, expansin genes are also present - but functionally uncharacterized - in taxonomically diverse bacteria and fungi that do not produce cellulosic cell walls. Here, we find that Erwinia tracheiphila (Enterobacteriaceae), the causative agent of bacterial wilt of cucurbits, has horizontally acquired an operon with a microbial expansin (exlx) gene and a glycoside hydrolase family 5 (gh5) gene. E. tracheiphila is an unusually virulent plant pathogen that induces systemic wilt symptoms followed by plant death, and has only recently emerged into cultivated cucurbit populations in temperate Eastern North America. Plant inoculation experiments with deletion mutants show that EXLX-GH5 is a secreted virulence factor that confers efficient xylem movement and colonization ability to E. tracheiphila. Bacterial colonization of xylem blocks sap flow, inducing wilt symptoms and causing plant death. Together, these results suggest that the horizontal acquisition of the exlx-gh5 locus was likely a key step driving the recent emergence of E. tracheiphila. The increase in E. tracheiphila virulence conferred by microbial expansins, the presence of this gene in many other bacterial and fungal wilt-inducing plant pathogen species, and the amenability of microbial expansins to horizontal gene transfer suggest this gene may be an under-appreciated virulence factor in taxonomically diverse agricultural pathogens.\n\nImportanceErwinia tracheiphila is a bacterial plant pathogen that causes a fatal wilt infection in cucurbit crop plants. Here, we report that E. tracheiphila has horizontally acquired a microbial expansin gene (exlx) adjacent to a glycoside hydrolase family 5 (gh5) gene. Expansins are predominantly associated with plants due to their essential role in loosening structural cell wall cellulose during normal growth. We find that the EXLX and GH5 proteins in E. tracheiphila function as a single complex to facilitate xylem colonization, possibly by manipulating the size of xylem structures that normally exclude the passage of bacteria. This suggests that horizontal acquisition of the exlx-gh5 locus was likely a key step in the recent emergence of E. tracheiphila as an unusually virulent plant pathogen. The presence of microbial expansin genes in diverse species of bacterial and fungal wilt-inducing pathogens suggests it may be an under-appreciated virulence factor for other microbes.

microbiology↗

bioRxiv2018

An introduced crop plant is driving diversification of the virulent bacterial pathogen Erwinia tracheiphila

Erwinia tracheiphila is the causal agent of bacterial wilt of cucurbits, an economically important phytopathogen affecting few cultivated Cucurbitaceae host plant species in temperate Eastern North America. However, essentially nothing is known about E. tracheiphila population structure or genetic diversity. To address this shortcoming, a representative collection of 88 E. tracheiphila isolates was gathered from throughout its geographic range, and their genomes were sequenced. Phylogenomic analysis revealed three genetic clusters with distinct hrpT3SS virulence gene repertoires, host plant association patterns, and geographic distributions. The low genetic variation within each cluster suggests a recent population bottleneck followed by population expansion. We showed that in the field and greenhouse, cucumber (Cucumis sativus), which was introduced to North America by early Spanish conquistadors, is the most susceptible host plant species, and the only species susceptible to isolates from all three lineages. The establishment of large agricultural populations of highly susceptible C. sativus in temperate Eastern North America may have facilitated the original emergence of E. tracheiphila into cucurbit agro-ecosystems, and this introduced plant species may now be acting as a highly susceptible reservoir host. Our findings have broad implications for agricultural sustainability by drawing attention to how worldwide crop plant movement, agricultural intensification and locally unique environments may affect the emergence, evolution, and epidemic persistence of virulent microbial pathogens.\n\nImportanceErwinia tracheiphila is a virulent phytopathogen that infects two genera of cucurbit crop plants, Cucurbita spp. (pumpkin and squash) and Cucumis spp. (muskmelon and cucumber). One of the unusual ecological traits of this pathogen is that it is limited to temperate Eastern North America. Here, we complete the first large-scale sequencing of an E. tracheiphila isolate collection. From phylogenomic, comparative genomic, and empirical analyses, we find that introduced Cucumis spp. crop plants are driving the diversification of E. tracheiphila into multiple, closely related lineages. Together, the results from this study show that locally unique biotic (plant population) and abiotic (climate) conditions can drive the evolutionary trajectories of locally endemic pathogens in unexpected ways.

evolutionary biology↗

bioRxiv2018

Amycomicin: a potent and specific antibiotic discovered with a targeted interaction screen

The rapid emergence of antibiotic-resistant pathogenic bacteria has accelerated the search for new antibiotics. Many clinically used antibacterials were discovered through culturing a single microbial species under nutrient-rich conditions, but in the environment, bacteria constantly encounter poor nutrient conditions and interact with neighboring microbial species. In an effort to recapitulate this environment we generated a nine-strain Actinomycete community and used 16S rDNA sequencing to deconvolute the stochastic production of antimicrobial activity that was not observed from any of the axenic cultures. We subsequently simplified the community to just two strains and identified Amycolatopsis sp. AA4 as the producing strain and Streptomyces coelicolor M145 as an inducing strain. Bioassay-guided isolation identified amycomicin, a highly modified fatty acid containing an epoxide isonitrile warhead as a potent and specific inhibitor of Staphylococcus aureus. Amycomicin targets an essential enzyme in fatty acid biosynthesis (FabH) and reduces S. aureus infection in a mouse skin infection model. The discovery of amycomicin demonstrates the utility of screening complex communities against specific targets to discover small-molecule antibiotics.\n\nSignificanceBacteria, especially actinomycetes, produce the majority of our clinically useful small-molecule antibiotics. Genomic analyses of antibiotic-producing strains indicate that earlier discovery efforts found only a fraction of the likely antibiotic candidates. In an effort to uncover these previously missed candidates we developed an approach that utilizes the ability of microbial communities to produce antibiotics that are not produced by any single member in isolation. Successful communities were established and deconvoluted to identify both producers and inducers of antibiotic activity. One inducer-producer pair made amycomicin, a potent and specific antibiotic against Staphylococcus aureus, an important human pathogen. Amycomicin targets fatty acid biosynthesis and exhibits in vivo efficacy against skin infections in a mouse model.

microbiology↗