Anckaert, A. | Search bioRxiv

bioRxiv2023

Deciphering the biology and chemistry of the mutualistic partnership between Bacillus velezensis and the arbuscular mycorrhizal fungus Rhizophagus irregularis

Arbuscular mycorrhizal (AM) fungi (e.g. Rhizophagus irregularis) recruit specific bacterial species in their hyphosphere. However, the chemical interplay and the mutual benefit of this intricate partnership have not yet been investigated especially as it involves bacteria known as strong producers of antifungal compounds such as Bacillus velezensis. Here, we show that the soil dwelling B. velezensis migrates along the hyphal network of the AM fungus R. irregularis, forming biofilms and inducing metabolic fluxes that contributes to host plant root colonization by the bacterium. During hyphosphere colonization, R. irregularis modulates the biosynthesis of specific lipopeptides and antimicrobial compounds in B. velezensis as a mechanism toward-off mycoparasitic fungi and bacteria to ensure stable coexistence. These mutual benefits are extended into a tripartite context via the provision of enhanced protection to the host plant through the induction of systemic resistance.

microbiology↗

bioRxiv2023

The fate of bacterial secondary metabolites in the rhizosphere: Streptomyces degrades and feeds on cyclic lipopeptides produced by competitors

Cyclic lipopeptides are key bioactive secondary metabolites produced by some plant beneficial rhizobacteria such as Pseudomonas and Bacillus. They exhibit antimicrobial properties, promote induced systemic resistance in plants and support key developmental traits including motility, biofilm formation and root colonization. However, our knowledge about the fate of lipopeptides once released in the environment and especially upon contact with neighboring rhizobacteria remains limited. Here, we investigated the enzymatic degradation of Bacillus and Pseudomonas cyclic lipopeptides by Streptomyces venezuelae. We observed that Streptomyces is able to degrade the three lipopeptides surfactin, iturin and fengycin upon confrontation with of B. velezensis in vitro and in planta according to specific mechanisms. S. venezuelae was also able to degrade the structurally diverse sessilin, tolaasin, orfamide, xantholisin and putisolvin-type lipopeptides produced by Pseudomonas, indicating that this trait is likely engage in the interaction with various competitors.Furthermore, the degradation of CLPs is associated with the release of free amino and fatty acids and was found to enhance Streptomyces growth, indicating a possible nutritional utilization. Thereby, this work stresses on how the enzymatic arsenal of S. venezuelae may contribute to its adaptation to BSMs-driven interactions with microbial competitors. The ability of Streptomyces to degrade exogenous lipopeptides and feed on them adds a new facet to the implications of the degradation of those compounds by Streptomyces, where linearization of surfactin was previously reported as a detoxification mechanism. Additionally, we hypothesize that lipopeptide-producing rhizobacteria and their biocontrol potential are impacted by the degradation of their lipopeptides as observed with the polarized motility of B. velezensis, avoiding the confrontation zone with Streptomyces and the loss of antifungal properties of degraded iturin. This work illustrates how CLPs, once released in the environment, may rapidly be remodeled or degraded by members of the bacterial community, with potential impacts on CLP-producing rhizobacteria and the biocontrol products derived from them.

microbiology↗