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.