Bioassay-Guided Isolation of a Low Molecular Weight PHB from Burkholderia sp. with Phytotoxic Activity

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

BACKGROUND

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.

RESULTS

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 9950T, 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.

CONCLUSION

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.

Bioactivity Profiling and Untargeted Metabolomics of Microbiota Associated with Mesopelagic Jellyfish Periphylla periphylla

The marine mesopelagic zone extends from water depths of 200 m to 1000 m and is home to a vast number and diversity of species. It is one of the least understood regions of the marine environment with untapped resources of pharmaceutical relevance. The mesopelagic jellyfish Periphylla periphylla is a well-known and widely distributed species in the mesopelagic zone; however, the diversity or the pharmaceutical potential of its cultivable microbiota has not been explored. In this study, we isolated microorganisms associated with the inner and outer umbrella of P. periphylla collected in Irminger Sea by a culture-dependent approach, and profiled their chemical composition and biological activities. Sixteen mostly gram-negative bacterial isolates were selected and subjected to an OSMAC cultivation regime approach using liquid and solid marine broth (MB) and glucose-yeast-malt (GYM) media. Their ethyl acetate (EtOAc) extracts were assessed for cytotoxicity and antimicrobial activity against fish and human pathogens. All, except one extract, displayed diverse levels of antimicrobial activities. Based on low IC₅₀ values, four most bioactive gram-negative strains; Polaribacter sp. SU124, Shewanella sp. SU126, Psychrobacter sp. SU143 and Psychrobacter sp. SU137, were prioritized for an in-depth comparative and untargeted metabolomics analysis using feature-based molecular networking. Various chemical classes such as diketopiperazines, polyhydroxybutyrates (PHBs), bile acids and other lipids were putatively annotated, highlighting the biotechnological potential in P. periphylla-associated microbiota as well as gram-negative bacteria. This is the first study providing an insight into the cultivable bacterial community associated with the mesopelagic jellyfish P. periphylla and, indeed, the first to mine the metabolome and antimicrobial activities of these microorganisms.

Tandem mass spectrometry methods to accelerate the identification of phytotoxic metabolites produced by Streptomyces sp. 39 PL

Natural products isolated by microorganisms are interesting in the search for new compounds with several biological activities. However, low concentration and structural diversity make the isolation a time-consuming step. Tandem mass spectrometry is a well-established technology for the identification and characterization of target microbial natural products due to high sensitivity and selectivity of these experiments. We developed a method employing neutral loss experiments (LC-ESI-MS/MS) to identify luminacins in microbial crude extracts. The luminacins class exhibited conserved fragmentation pattern with loss at 172 Da relative to glycosides fragment and this loss was used in searching for compounds belonging to this class. Therefore, the crude extract produced by Streptomyces sp. 39 PL was analysed and five luminacins were isolated - one is a novel luminacin I at 466 Da.