Diversity, antibacterial and phytotoxic activities of actinomycetes associated with .

Background: Insect-associated actinomycetes represent a potentially rich source for discovering bioactive metabolites. However, the diversity, antibacterial and phytotoxic activities of symbiotic actinomycetes associated with have not yet been conducted.

Results: A total of 86 strains of actinomycetes were isolated from the cornicles and intestines of both nymphs and adults of . Diversity analysis revealed that the isolated strains were preliminarily identified as 17 species from two genera, and the dominant genus was . A total of 36 crude extracts (60%) obtained from the supernatant of the 60 fermented strains exhibited a potent antibacterial activity against at least one tested pathogenic bacterium. Among these active strains, 27 crude extracts (75%) exhibited phytotoxic activity against the radicle of . Furthermore, seven known compounds, including methoxynicotine (), (3Z,6Z)-3-(4-methoxybenzylidene)-6-(2-methylpropyl) piperazine-2,5-dione (), XR334 (), 1-hydroxy-4-methoxy-2-naphthoic acid (), nocapyrone A (), β-daucosterol (), and β-sitosterol () were isolated from an active rare actinomycete sp. ZLC-87 which was isolated from the gut of adult . Among them, compound exhibited moderate antibacterial activity against , , , and pv. with the zone of inhibition (ZOI) of 14.5, 12.0, 12.5, and 13.0 mm at a concentration of 30 μg/disc, respectively, which was weaker than those of gentamicin sulfate (ZOI of 29.5, 19.0, 18.5, and 24.5 mm). In addition, the compound had potent phytotoxic activity against the radicle of and with the inhibition rate of 65.25% and 92.68% at the concentration of 100 μg/mL.

Conclusion: Based on these findings, this study showed that -associated actinomycetes held promise for the development of new antibiotic and herbicide resources.