A gut symbiotic filamentous fungus reprograms host metabolism and the microbiota to confer radioprotection.

A metabolite-dependent mechanism by which Bifidobacterium animalis subsp. lactis promotes Bacteroides colonization

B. animalis subsp.

Understanding metabolic interactions between bacteria and fungi for cross-kingdom consortia applications.

Bacterial-fungal interactions represent fundamental ecological associations that shape microbial community structure across diverse environments. While traditionally framed through the lens of antagonism, bacteria and fungi engage in sophisticated metabolic dialogs extending far beyond simple warfare. Both primary and specialized metabolites function as context-dependent signals, nutrient resources, and modulators of cellular processes that fundamentally influence the physiology, development, and evolutionary trajectory of both fungi and bacteria. Primary metabolites mediate mutualistic relationships through cross-feeding and syntrophy, while specialized metabolites, including volatile organic compounds, lipopeptides, and phenazines, modulate fungal physiology at sub-inhibitory concentrations, reprogramming metabolic networks and triggering adaptive responses without causing cell death. At the molecular level, bacterial metabolites regulate fungal gene expression through transcriptional reprogramming, with consequences that extend to long-term evolutionary adaptation. The complexity of Bacillus-Trichoderma interactions exemplifies how these principles translate into ecological outcomes, exhibiting context-dependent transitions from competition to synergism that enhance biocontrol efficacy, plant growth promotion, and organic matter turnover. Recognizing the multifunctional nature of microbial metabolites beyond direct toxicity opens new avenues for rationally engineering cross-kingdom consortia with targeted agricultural and biotechnological applications.

Metabolic shifts driven by host-microbial interactions.

Mycorrhiza helper bacteria as stage-specific modulators of fungal development

The rhizosphere is a narrow and dynamic soil zone where bacteria and fungi establish symbiotic and synergistic relationships with each other and with plants, collectively influencing nutrient cycling, soil health, and overall ecosystem functioning. Mycorrhiza Helper Bacteria (MHB) are a diverse group of bacterial taxa that promote mycorrhiza establishment, together with those that positively influence already established symbiotic associations. MHB have been largely described from the perspectives of interaction mechanisms, ecological functions, or agricultural applications, treating them as generalized fungal growth-promoters or biofertilizers. However, how their effects change throughout fungal development has received little attention. This review addresses this knowledge gap by reframing MHB not as generic growth promoters, but as stage-specific regulators of the fungal development program. We integrate current evidence on transcriptional responses, metabolite-mediated signaling, and emerging small RNA regulatory networks across five sequential phases of the fungal life cycle: spore germination, presymbiotic hyphal growth, mycelial expansion, root colonization, and nutrient uptake. Elucidating these stage-specific regulatory mechanisms may provide the basis for the rational, stage-targeted design of MHB-based innovative strategies for sustainable agriculture.

Pollen Polysaccharides Drive the Strain-Level Assembly and Competitive Dynamics of Bifidobacterium in the Honeybee Gut.

The gut microbiota orchestrates host health by influencing nutrition, immunity, and behavior. Bifidobacterium species are early colonizers maintaining gut homeostasis in honeybees. Despite these critical roles, strain-level dynamics and driving forces behind microbial competition during social transmission remain poorly understood. Here, we established six field-mimicking colonies to track Bifidobacterium communities across successive generations of newly emerged workers. Social transmission markedly reshaped community structure, generating distinct trajectories among phylotypes. OTU10 consistently dominated, reaching a median relative abundance of 77%, whereas OTU61 and OTU43146 were progressively outcompeted or lost. Comparative genomics of five representative species identified 69 carbohydrate-active enzyme families, with GH43 glycosyl hydrolases driving genomic divergence. Bifidobacterium polysaccharolyticum encoded an expanded CAZyme repertoire, supporting rapid growth on glucose and arabinan and indicating an r-selected strategy. In vitro and in vivo competition assays demonstrated that nutrient availability and priority effects act as key ecological filters. Pollen favored Bifidobacterium apousia, whereas sucrose-only diets promoted B. polysaccharolyticum. Moreover, early colonizers excluded later arrivals to some extent, highlighting priority effects. Together, these findings reveal how pollen polysaccharides and transmission bottlenecks interact to structure the strain-level landscape of the social microbiome.

Extensin-enriched host cell wall specialization restricts fungal invasion while sustaining symbiosis in the mycoheterotrophic orchid, Gastrodia elata.

BACKGROUND Fully mycoheterotrophic orchids depend entirely on fungal partners for carbon and mineral nutrition, yet the structural mechanisms that regulate fungal accommodation within host tissues remain poorly understood. This question is particularly relevant in the Gastrodia elata-Armillaria symbiosis, where the fungal partner is a wood-decaying basidiomycete capable of aggressive host colonization and responsible for root rot disease in many tree species. Here, we examined whether host cell wall remodeling and extensin deposition contribute to the establishment and regulation of the host-fungus interface in G. elata tubers. RESULTS Ultrastructural analyses revealed extensive host-derived cell wall remodeling during fungal colonization of G. elata tubers, including localized wall thickening and the formation of hypha-encasing wall domains within fungal-colonized cells and adjacent boundary cells. Comprehensive Microarray Polymer Profiling identified extensin epitopes recognized by JIM20 as the most strongly enriched hydroxyproline-rich glycoproteins component following colonization. Immunogold labeling localized extensin-enriched HRGPs specifically to modified host cell walls and interfacial matrices surrounding intracellular hyphae. Quantitative comparison demonstrated that the interfacial matrix surrounding intracellular hyphae was substantially thicker than that reported for arbuscular or typical orchid mycorrhizal associations. Chemical inhibition of HRGPs deposition using 3,4-DHP disrupted interfacial wall formation, resulting in uncontrolled fungal spread into normally restricted tissues, cortical necrosis, and reduced tuber growth. CONCLUSIONS Our findings demonstrate that extensin-enriched host cell wall remodeling establishes a reinforced symbiotic interface that spatially restricts fungal invasion while maintaining potential routes for nutrient exchange. Our results reveal a structural mechanism enabling a fully mycoheterotrophic orchid to accommodate an invasive fungal symbiont, indicating that spatial compartmentalization of host-fungus interactions represents an important mechanism contributing to symbiotic stability.