Novel phytotoxic compounds from Streptomyces sp. Caat 7-52: a potential bioherbicide against Conyza canadensis

The rise of herbicide-resistant weeds like Conyza canadensis L. poses a challenge to modern agriculture, driving the need for eco-friendly alternatives. Microbial metabolites from actinobacteria species offer promising weed-control solutions. This study aims to screen and identify an actinobacteria isolate from Brazil's Caatinga biome that produces phytotoxic metabolites and to characterize its compounds.

An isolate, named as Caat 7-52, was selected because of its significant phytotoxic effects against Lemna minor L. Phylogenetic analyses using six concatenated genes (gyrB, recA, rpoB, trpB, atpD and 16S rRNA) confirmed Caat 7-52's close relationship to Streptomyces musisoli TBRC 9950^T, despite phenotypical differences. Bioassay-directed isolation against L. minor revealed 3-hydroxybenzoic acid and albocycline as phytotoxins, with minimum inhibitory concentrations of 50.00 and 3.12 μg mL^-1, respectively. Albocycline analogues were also detected and exhibited moderate phytotoxicity in L. minor. In addition, albocycline effectively inhibited the seed germination of C. canadensis with a minimum inhibitory concentration of 6.25 μg mL^-1, marking the first report of albocycline's phytotoxic activity. Direct use of the fermented broth selectively inhibited dicot weeds, offering a sustainable and solvent-free weed management strategy.

The discovery of Streptomyces sp. Caat 7-52 and its metabolites, combined with the direct application of fermented broth, represents a significant advancement in sustainable weed control. This bioherbicidal approach offers an environmentally friendly alternative for managing resistant weeds like C. canadensis and supports the broader use of microbial metabolites in integrated pest management programs. © 2025 Society of Chemical Industry.