Tryptophan-Driven Metabolomic Shift in Acidobacteriaceae Reveals Phytohormones and Antifungal Metabolites

Acidobacteriota is one of the most abundant phyla in soils and has recently attracted attention for its potential role in promoting phytosanitary benefits. The metabolomic capabilities of this phylum remain poorly characterised, with few experimentally confirmed metabolites described. To address these gaps, we combined metabolomic profiling with comparative genomic analysis to explore the functional potential of novel strains within the Acidobacteriaceae family. Genome mining across the phylum for PGPTs revealed the presence and taxon-specific enrichment of genes related to phytohormone production, as well as other genes associated with plant-growth-promoting effects. When tryptophan (Trp) was added to the cultivation medium, it triggered a strong metabolic response in the strains, resulting in measurable changes in the production levels of phytohormones such as indole-3-acetic acid (IAA) and indole-3-pyruvate (iP). Building on these findings, we examined the metabolic reprogramming caused by Trp supplementation, which suppressed the growth of phytopathogenic fungi, leading to the identification of malassezindoles and pityriacitrins as active agents. This was confirmed by isolating and elucidating the structure of pityriacitrin B and a methyl ester through NMR studies. Overall, these findings shed light on the previously unexplored metabolic potential of the Acidobacteriota phylum, emphasising its ecological importance for phytosanitary applications.