Plant-associated Streptomyces detoxify the mycotoxin fusaric acid by amino acid conjugation

Streptomycetes are prevalent members of soil and plant microbiomes, yet how they cope with toxins produced by root-infecting fungal pathogens remains poorly understood. Plant pathogenic Fusarium species produce the mycotoxin fusaric acid (FA) that contributes to virulence and perturbs rhizosphere microbiome dynamics. Here, we show that root-colonising Streptomyces sp. ATMOS43 neutralizes FA through amino acid conjugation. Metabolomics revealed the formation of single amino acid and dipeptidyl conjugates of FA, with FA-Ser as a major conjugate that lacked detectable toxicity in in vitro and in planta assays. Proteomics and physiological analyses revealed that FA toxicity involves, in part, zinc chelation, which is abolished upon conjugation of FA to Ser. Co-cultivation experiments further showed that Streptomyces sp. ATMOS43 restores growth of FA-sensitive streptomycetes, indicating that conjugation can mitigate the impact of FA on plant microbiome assembly. Together, our findings show that plant-associated streptomycetes can protect plants by directly inhibiting Fusarium growth and by neutralizing its toxic virulence factor FA.