ИСТИНА

The emergence and rapid development of microbial resistance to antibacterial drugs is one of the major problems for modern science and medicine. The discovery of new antibacterial compounds may help to solve the problem, and soil bacteria still remain one of the most promising sources of bioactive natural products. We have recently developed an optimized workflow for screening, isolation and identification of new antibiotics in the course of the Citizen Science project. The workflow has been applied in practice, revealing two actinomycete strains, Streptomyces sp. 44182 and 37078, producing potentially new peptide antibiotics. Optimal cultivation conditions have been determined and fermentation broths have been subjected to solid-phase extraction on LPS-500-H resin. Subsequent activity-guided HPLC analysis of active fractions has been used, since the separation of such biological mixtures is often complicated due to impurities of a similar chemical nature and the degradation of target substances over time, which significantly hampers detection. For each analyte, HPLC conditions were repeatedly refined to identify the exact localization of the active substance. Then, active pure fractions have been analyzed with highresolution mass spectrometry (HRMS) in both positive and negative ionization modes with fragmentation of the three most abundant ions. As a result, two strains Streptomyces sp. 44182 and 37078 were found to produce bioactive compounds with very similar fragmentation patterns and calculated exact masses: 2154.736 Da and 2168.763 Da, respectively. No matches were found in the databases of natural products for these compounds. A mass difference of 14.027 Da probably corresponds to one −CH2 unit. Further MALDI-TOF mass spectrometry analysis has proved the peptide nature of new antibiotics and their belonging to the class of lassopeptide antibiotics. This research was funded by the Ministry of Science and Higher Education of the Russian Federation (Agreement NO.075–15-2021-1085).