Vertot, M. | Search bioRxiv

bioRxiv2025

Penicillium hordei acidification precipitates Bacillus subtilis lipopeptides to evade inhibition

Interkingdom interactions are crucial for community and ecosystem functioning, however secondary metabolites mediating interactions between plant beneficial bacteria and fungi remain understudied. Penicillium and Bacillus species can individually suppress soilborne phytopathogens and promote plant growth. Here, we showed that Penicillium hordei and Bacillus subtilis co-culture led to precipitation of B. subtilis lipopeptides, observed as white line in agar. Metabolomic analysis revealed B. subtilis triggered enhanced production of fungal terrestric acid and its biosynthetic intermediates, which induced lipopeptide precipitation to prevent P. hordei inhibition by chemical inactivation and physical barrier formation. Besides lipopeptide precipitation, terrestric acid-mediated acidification progressively reduced production of antifungal plipastatins. The lack of lipopeptide production permitted P. hordei to invade and overgrow B. subtilis colony. We demonstrated that the white line phenomenon was conserved among closely related fungi via secretion of terrestric, fulvic or barceloneic acids. Furthermore, terrestric acid at specific concentrations acted as a universal metabolite that drives B. subtilis lipopeptide precipitation even in distantly related fungi. This study provides new insights into acidification as a fungal defensive strategy that may promote co-existence with beneficial bacteria exhibiting strong antagonistic potential, thereby contributing to the formation of a stable rhizosphere community.

microbiology↗

bioRxiv2024

Coupling of secondary metabolite production in Bacillus subtilis

Although not essential for their growth, the production of secondary metabolites increases the fitness of the producing microorganisms in their natural habitat by enhancing establishment, competition and nutrient acquisition. The Gram-positive soil-dwelling bacterium, Bacillus subtilis produces a variety of secondary metabolites. Here, we investigated the regulatory relationship between the non-ribosomal peptide surfactin and the sactipeptide bacteriocin subtilosin A. We discovered that B. subtilis mutants lacking surfactin production exhibited higher production of subtilosin A compared to their parental wild-type strain. Additionally, spatial visualization of B. subtilis production of metabolites demonstrated that surfactin secreted by a wild-type colony could suppress subtilosin A production in an adjacent mutant colony lacking surfactin production. Reporter assays were performed using mutants in specific transcriptional regulators that confirmed the role of ResD as an activator of the subtilosin A encoding BGC, while removal or Rok and AbrB repressors increased expression of the BGC that was further enhanced by additional deletion of surfactin, suggesting that a so far unidentified regulator might mediate the influence of surfactin on production of subtilosin A. Our study reveals a regulatory influence of one secondary metabolite on another, highlighting that the function of secondary metabolites could be more complex than its influence on other organisms and interactions among secondary metabolites could also contribute to their ecological significance. ImportanceSecondary metabolites play an important role in the life of microorganisms facilitating their fitness in the environment, including competing against other microorganisms, interacting with their host or environment, and allowing expansion in their environment. However, secondary metabolites also function as cue molecules influencing gene expression between and within species. Here, we describe that the non-ribosomally synthesized peptide surfactin repress the production of ribosomally synthesized and post translationally modified peptide, subtilosin A in Bacillus subtilis, revealing an ecological interaction between two secondary metabolites that could potentially influence the biocontrol efficiency of B. subtilis strain that depends on the production of these secondary metabolites against plant pathogen microorganisms.

microbiology↗