The study of antibiotic producers from natural sources plays an important role in the development of new drugs. One way to search for antibiotics is the isolation of microbial antibiotic producers from insects and their products [1]. Symbionts and insect-associated microorganisms represent an almost inexhaustible source of bioactive compounds, including antibiotics [2].

In this study, we examined samples of the bark beetle typographus (Ips typographus) found in the bark of fallen spruce (Picea). The bodies of insects, previously sedated with diethyl ether, were prewashed with 80% ethyl alcohol to exclude external contaminants. Then, they were homogenized using a sterile glass rod. The obtained mass was suspended in sterile water for inoculation. The inoculum was spread on 9 × 9 cm Petri dishes with brain heart infusion solid nutrient medium (with nystatin, 50 μg/mL), potato dextrose (with tobramycin, 25 μg/mL), nutrient agar (with nystatin, 50 μg/mL), and nutrient agar (with nystatin, 50 μg/mL, and nalidixic acid, 30 μg/mL). A total of 113 microbial isolates were obtained. Antimicrobial activity was screened using the agar diffusion method against a wide range of test microorganisms: a fungus (A. niger INA 00760), a yeast (C. albicans CBS 8836), Gram-positive bacteria (B. subtilis ATCC 6633, E. faecalis ATCC 29212), and Gram-negative bacteria (E. coli ATCC 25922).

As a result, three isolates of micromycetes with pronounced antimicrobial properties were selected for further study and cultivation in liquid nutrient media. The acitve substances were identified by LC-MS. Strain K1-26 produced harzianic acid. Strain K4-28 produced aspergillic acid. Strain K2-6 produced several antibiotic substances: verruculogen, fumagillin, helvolic acid, and helvolinic acid.

This work was supported by the Russian Science Foundation, project no. 25-14-00281.

1 A. A. Baranova et al., Microorganisms, 2020, 8, 1948.

2 A. A. Baranova et al., Biology, 2022, 11, 1676.