Biology subjects

Vannette, R.

Publications and source records attributed to Vannette, R..

11 recordsLinked to original sources

bioRxiv2026

Temperate Phage Shape Honey Bee Gut Microbiome Structure and Response to Antibiotic Treatment

Bacteriophage (phage) are hypothesized to play a significant role in modulating gut microbiomes. Yet, in vivo research examining the role of phage in gut ecosystems remains sparse, largely due to a lack of tractable model systems. Here, we use the honey bee (Apis mellifera) gut as a model to test the hypotheses that phage-bacteria interactions in the gut are temporally variable and that stress, in the form of antibiotics, can enhance phage killing of their bacterial hosts. First, we isolated and characterized a novel temperate phage which infects a bee-specific strain of Bifidobacterium. We then mono-colonized adult honey bees with this Bifidobacterium strain and tested how phage treatment impacts bacterial abundance over time. Next, using a series of in vitro and in vivo experiments, we examined how phage-bacteria interactions change in response to treatment with tetracycline, an antibiotic commonly used in commercial beekeeping. Finally, to probe the biological mechanisms underlying different phage-antibiotic synergies, we assayed how different classes of antibiotics impacted bacterial growth with and without phage infection. Our results indicate that a single temperate phage can both promote the ability of its Bifidobacterium host to colonize the gut, while also increasing host sensitivity to antibiotic treatment. Together, these findings demonstrate that environmental stressors can shift phage-bacteria interactions from mutualism to antagonism, highlighting the significance of phage in shaping how gut microbiomes respond to antibiotic or xenobiotic perturbation.

microbiology↗

bioRxiv2026

Comparative nectar metabolomics reveals sucrose-nitrogen tradeoffs and chemical drivers of microbial growth in floral nectar

IntroductionMany plant species secrete nectar to attract beneficial animals. The chemical composition of floral nectar influences pollinator nutrition and behavior, as well as microbial growth in flowers. Yet factors that predict nectar composition across plant species, as well as chemical compounds determining microbial growth in nectar, remain poorly understood. MethodsWe used both targeted and untargeted metabolomics to compare the nectar chemical profiles across 31 phylogenetically diverse plant species that span a range of floral morphologies. We examined the common classes of compounds detected in nectar and patterns of co-occurrence among them. We combined newly collected chemical data with previously published data on microbial growth in nectar of the same plant species to examine how nectar chemistry is associated with microbial growth. ResultsPlant species and clades varied in amino acid, minor sugar, and secondary metabolite composition and concentration. Sampled rosids and lilioids generally contained higher amino acids while asterids contained greater concentrations of oligosaccharides and sugar alcohols. Across plant species, proteinogenic amino acids frequently co-occurred in nectar but many were negatively associated with sucrose concentration. Plant species with greater concentrations of amino acids and other nitrogen-containing compounds hosted greater microbial density in nectar, while some other compound groups were negatively associated with microbial diversity. ConclusionsNegative correlations between nectar amino acid and sucrose concentration across species suggest ecological tradeoffs or physiological constraints in nectar composition. Given that the growth of common nectar microbes is limited by amino acid concentration, these findings suggest an ecological cost to amino acid production in nectar. Finally, we document variation among species in nectar vitamins, non proteinogenic amino acids and secondary metabolites with hypothesized yet currently untested ecological roles.

plant biology↗

bioRxiv2025

Floral microbes provisioned by Osmia lignaria establish in larval food stores, but do not affect bee development or survival

Microbial dispersal and subsequent establishment among linked habitats can be used to examine drivers of community assembly and function. Flowers host microbial communities that can be acquired and vectored by bees to new flowers, establish within the adult bee gut, and enter food stores (e.g., pollen provisions) of developing larvae. Yet, whether microbes vectored by insects or applied for biocontrol can establish across these habitats and if they affect bee fitness remain unknown. Here, we applied microbes to flowers visited by blue orchard bees (Osmia lignaria) and compared microbial communities in flowers, adult bee guts, and pollen provisions before and after inoculation to determine microbial establishment, environmental filtering, and overlap across habitat types. We also inoculated provisions with microbes to test their effects on larval survival and development. Experimentally inoculated microbes were detected in all habitats, demonstrating that flowers are a source of microbial acquisition for adult and larval bees. Additionally, larval health was not impacted by microbe supplementation, indicating tolerance of bee larvae to floral microbes in Osmia.

microbiology↗

bioRxiv2025

Pollen diet, more than geographic distance, shapes provision microbiome composition in two species of cavity-nesting bees

The microbial composition of stored food can influence its stability and determine the microbial species consumed by the organism feeding on it. Many bee species store nectar and pollen in provisions constructed to feed developing offspring. Previous work has shown variation in provision microbiome among bee populations, yet whether this variation is determined by the pollen types within provisions, variation between bee species at the same nesting sites, or geographic distance was unclear. Here, we sampled two species of co-occurring cavity nesting bees in the genus Osmia at 13 sites across the Sierra foothills in California and examined the composition of pollen, fungi and bacteria found in their provisions across sites. As expected, pollen, bacterial and fungal composition exhibited significant turnover between bees and sites, with bee species characterized by particular pollen and microbial species. Pollen composition explained 15% of variation in bacterial composition and [~]30% of variation in fungal composition, whereas spatial distance among sites explained minimal additional variation. Symbiotic or bee-specialized microbe genera Ascosphaera, Sodalis and Wolbachia showed contrasting patterns of association with pollen composition, suggesting distinct acquisition and transmission routes for each. Comparing provisions from both bee species comprised of the same pollens points to environmental acquisition rather than bee species as a key factor shaping the early stages of the bee microbiome in Osmia. The patterns we observed also contrast with Apilactobacillus-dominated provision microbiome in other solitary bee species, suggesting variable mechanisms of microbial assembly in stored food among bee species.

ecology↗

bioRxiv2024

Effects of live yeasts and their metabolic products on bumble bee microcolony development

Bumble bees can benefit from fungi, though the mechanisms underlying these benefits remain unknown and could include nutrition, resource supplementation, or pathogen protection. We tested how adding living yeasts or their metabolic products to Bombus impatiens diets in a factorial experiment affects microcolony performance, including survival, reproduction, and pathogen presence. We additionally assessed effects of yeast treatments on diet (nectar and pollen) chemical composition using untargeted metabolomics. Yeasts impacted microcolony reproduction and survival, but effects depended on source colony. Colonies containing the putative pathogen Aspergillus showed reduced reproduction, but yeast treatments reduced Aspergillus prevalence. Yeast treatments altered chemical composition of nectar and pollen, but most distinguishing compounds were unidentified. Our results suggest limited direct effects of yeasts via nutrition, resource supplementation, or modification of diets, instead suggesting that yeasts may benefit bees through interactions with the pathogens including Aspergillus. Overall, the effects of yeast supplementation are context-dependent, and more research is necessary to better understand the factors important in determining their impacts on bee hosts.

ecology↗

bioRxiv2024

Plant species vary in nectar peroxide, an antimicrobial defense tolerated by some bacteria and yeasts

Floral nectar attracts pollinators but can also harbor microbes including plant pathogens. Nectar contains antimicrobial constituents including hydrogen peroxide, yet it is unclear how widespread nectar hydrogen peroxide might be among plant species or how effective against common nectar microbes. Here, we surveyed 45 flowering plant species distributed across 23 families and reviewed the literature for measurements of 13 other species to assess the field-realistic range of nectar hydrogen peroxide (Aim 1) and explored whether plant defense hormones induce nectar hydrogen peroxide upregulation (Aim 2). Further, we tested the hypotheses that variation in microbial tolerance to peroxide is predicted by microbe isolation environment (Aim 3), that increasing hydrogen peroxide in flowers alters microbial abundance and community assembly (Aim 4), and that microbial community context affects microbial tolerance to peroxide (Aim 5). We found that sampled plants contained nectar hydrogen peroxide ranging from 0 to 2940 {micro}M, although half of the sampled species concentrations were less than 100 {micro}M. While plant defensive hormones did not change the concentration of hydrogen peroxide in floral nectar, enzymatically upregulated concentrations in living flowers significantly reduced microbial growth. Together, our results suggest that nectar peroxide is a common but not pervasive antimicrobial defense among nectar-producing plants. In addition, nectar microbes vary in tolerance and detoxification ability, and co-growth can facilitate the survival and growth of less tolerant species, suggesting a key role for community dynamics in microbial colonization of nectar.

plant biology↗

bioRxiv2021

Population-specific patterns of toxin sequestration in monarch butterflies from around the world

Animals frequently defend themselves against predators using diet-derived toxins. Monarch butterflies are a preeminent example of toxin sequestration, gaining protection via cardenolides in their milkweed hosts. Few studies have considered genetic variation in sequestration ability, in monarchs or other species. Here, we use two approaches to study natural selection on cardenolide sequestration in monarchs. First, we conducted a reciprocal rearing experiment with six monarch populations and six associated host species from around the world to determine whether sequestration is higher in monarchs reared on sympatric host species. Second, we compared sequestered cardenolides in wild-caught monarchs from Guam--an island where bird predators have been functionally extirpated for >40 years--to a nearby island with intact birds. We found substantial genetic variation in sequestration ability, though no consistent sequestration advantage in sympatric combinations. One monarch population from Puerto Rico showed greatly reduced sequestration from Asclepias syriaca, likely reflecting a lack of evolutionary association with this host. Monarchs from Guam showed reduced sequestration from A. curassavica, both in a cross-island comparison and when reared under controlled conditions. Our results suggest that processes involved in toxin sequestration are subject to natural selection and may evolve in response to contemporary changes in species interactions.

evolutionary biology↗

bioRxiv2021

Plant phenology influences rhizosphere microbial community and is accelerated by serpentine microorganisms in Plantago erecta

Serpentine soils are drought-prone and rich in heavy metals, and plants growing on serpentine soils host distinct microbial communities that may affect plant survival and phenotype. However, whether the rhizosphere communities of plants from different soil chemistries are initially distinct or diverge over time may help us understand drivers of microbial community structure and function in stressful soils. Here, we test the hypothesis that rhizosphere microbial communities will converge over time (plant development), independent of soil chemistry and microbial source. We grew Plantago erecta in serpentine or nonserpentine soil, with serpentine or nonserpentine microbes and tracked plant growth and root phenotypes. We used 16S rRNA barcoding to compare bacterial species composition at seedling, vegetative, early-, and late-flowering phases. Plant phenotype and rhizosphere bacterial communities were mainly structured by soil type, with minor contributions by plant development, microbe source and their interactions. Serpentine microorganisms promoted early flowering in plants on non-serpentine soils. Despite strong effects of soil chemistry, the convergence in bacterial community composition across development demonstrates the importance of the plant-microbe interactions in shaping microbial assembly processes across soil types.

microbiology↗

bioRxiv2021

Nectar bacteria stimulate pollen germination and bursting to enhance their fitness

For many flower visitors, pollen is the primary source of non-carbon nutrition, but pollen has physical defenses that make it difficult for consumers to access nutrients. Nectar-dwelling microbes are nearly ubiquitous among flowers and can reach high densities, despite the fact that floral nectar is nitrogen limited, containing only very low concentrations of non-carbon nutrients. Pollen contains trace micronutrients and high protein content but is protected by a recalcitrant outer shell. Here, we report that a common genus of nectar-dwelling bacteria, Acinetobacter, exploits pollen nutrition by inducing pollen germination and bursting. We use time course germination assays to quantify the effect of Acinetobacter species on pollen germination and pollen bursting. Inoculation with Acinetobacter species resulted in increased germination rates within 15 minutes, and bursting by 45 minutes, as compared to uninoculated pollen. The pollen germination and bursting phenotype is density-dependent, with lower concentrations of A. pollinis SCC477 resulting in a longer lag time before the spike in germination, which is then closely followed by a spike in bursting. Lastly, A. pollinis grows to nearly twice the density with germinable pollen vs ungerminable pollen, indicating that their ability to induce and exploit germination plays an important role in rapid growth. To our knowledge, this is the first direct test of non-plant biological induction of pollen germination, as well as the first evidence of induced germination as a method of nutrient procurement, as the microbes appear to hijack the pollens normally tightly controlled germination mechanisms for their benefit. Our results suggest that further study of microbe-pollen interactions may inform many aspects of pollination ecology, including microbial ecology in flowers, the mechanisms of pollinator nutrient acquisition from pollen, and cues of pollen germination for plant reproduction.

ecology↗

bioRxiv2020

Orchard management and landscape context mediate the floral microbiome of pear

Crop-associated microbiota are key factors affecting host health and productivity. Most crops are grown within heterogeneous landscapes, and interactions between management practices and landscape context often affect plant and animal biodiversity in agroecosystems. However, whether these same factors typically affect crop-associated microbiota is less clear. Here, we assessed whether orchard management strategies and landscape context affected bacterial and fungal communities in pear (Pyrus communis) flowers. We found that bacteria and fungi responded differently to management schemes. Organically-certified orchards had higher fungal diversity in flowers than conventional or bio-based integrated pest management (IPM) orchards, but organic orchards had the lowest bacterial diversity. Orchard management scheme also best predicted the distribution of several important bacterial and fungal genera that either cause or suppress disease, with organic and bio-based IPM best explaining the distributions of bacterial and fungal genera, respectively. Moreover, patterns of bacterial and fungal diversity were affected by interactions between management, landscape context, and climate. When examining the similarity of bacterial and fungal communities across sites, both abundance- and taxa-related turnover were mediated primarily by orchard management scheme and landscape context, and specifically the amount of land in cultivation. Our study reveals local- and landscape-level drivers of floral microbiome structure in a major fruit crop, providing insights that can inform microbiome management to promote host health and high-yielding quality fruit. IMPORTANCEIn tree fruits, proper crop management during bloom is essential for producing disease-free fruit. Tree fruits are often grown in heterogeneous landscapes; however, few studies have assessed whether landscape context and crop management affect the floral microbiome, which plays a critical role in shaping plant health and disease tolerance. Such work is key for identification of tactics and/or contexts where beneficial microbes proliferate, and pathogenic microbes are limited. Here, we characterize the floral microbiome of pear crops in Washington State, USA, where major production occurs in inter-mountain valleys and basins with variable elevation and microclimates. Our results show that both local (crop management) and landscape (habitat types and climate) level factors affect floral microbiota, but in disparate ways for each kingdom, suggesting a need for unique management strategies for each group. More broadly, these findings can potentially inform microbiome management in orchards for promotion of host health and high-quality yields.

microbiology↗

bioRxiv2020

Fungi are more dispersal-limited than bacteria among flowers

Variation in dispersal ability among taxa affects community assembly and biodiversity maintenance within metacommunities. Although fungi and bacteria frequently coexist, their relative dispersal abilities are poorly understood. Nectar-inhabiting microbial communities affect plant reproduction and pollinator behavior, and are excellent models for studying dispersal of bacteria and fungi in a metacommunity framework. Here, we assay dispersal ability of common nectar bacteria and fungi in an insect-based dispersal experiment. We then compare these results to the incidence and abundance of culturable flower-inhabiting bacteria and fungi within naturally occurring flowers across two coflowering communities in California across two flowering seasons. Our microbial dispersal experiment demonstrates that bacteria disperse among habitat patches more readily than fungi via thrips. Across all flowers, bacterial and fungal incidence and abundance were positively correlated but bacteria were much more widespread, suggesting shared dispersal routes or habitat requirements but differences in dispersal and colonization frequency. The finding that bacteria are more common among flowers sampled here, in part due to superior insect-mediated dispersal, may have broad relevance for microbial life-history, community assembly of microbes and plant-pollinator interactions.

ecology↗