Because of the spread of drug resistance, it is necessary to look for new antibiotics that are effective against pathogenic microorganisms. The purpose of this study was to analyse the species composition of actinobacteria isolated from the digestive tract of the millipedes Nedyopus dawydoffiae and to determine their antimicrobial properties. Species identification was carried out on the basis of the morphological and culture properties and the sequence of the 16S rRNA gene. Actinobacteria were grown in different liquid media. Antibiotic properties were determined against some Gram-positive and Gram-negative bacteria as well as fungi. Of the 15 isolated strains, 13 have antibiotic activity against Gram-positive bacteria (including methicillin-resistant Staphylococcus aureus—MRSA) and fungi, but there was no antibiotic activity against Gram-negative test strains Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853. It was established that antibiotic-producing actinobacteria belong to eight species of the genus Streptomyces. Depending on the nutrient medium, actinobacteria demonstrate different antimicrobial activities. As an example, S. hydrogenans shows that even strains selected in one population differ by the range of antimicrobial activity and the level of biosynthesis. Since the antibiotic production is considered as a feature for species competition in the microbiota community, the variability of antibiotic production among different strains of the same species is an adaptive characteristic for the competition in millipedes’ digestive tract community.
The antibiotic INA 2770 active against methicillin resistant staphylococcus aureus (MRSA) was biotechnologically produced and isolated. This antibiotic is identical to cineromycin B. The characteristic features of the 1 H and 13 C NMR spectra of this compound were studied for the first time, and the conformational analysis was carried out by computational methods (molecular mechanics (MM3) force field) and using nuclear Overhauser effect experiments.
In this study, the microbial communities of two nests of black garden ants (Lasius niger) in the hollows of stem branches of old apple trees were found to have similar species compositions: each community contained representatives of three species from the Bacillaceae family and one species of actinomycetes from the genus Streptomyces. In total, four types of bacilli and two actinomycetes were isolated. Actinomycetes were identified as Streptomyces antibioticus-like and Streptomyces sp. None of the bacilli had antibiotic activity, whereas both streptomycetes produced antibiotics that inhibited the growth of Gram-positive bacteria in vitro, including isolates from their community. Antibiotic compounds of S. antibioticus-like strain INA 01148 (Institute of New Antibiotics) were identified as actinomycin D and its closest homologue, actinomycin A. Actinomycins presumably change the microbial community of the ant nest substrate as they act against Gram-positive bacteria and against fungi and Gram-negative bacteria. The antibiotic activity of the isolated Streptomyces sp. INA 01156 is of interest, since the substances produced by this strain inhibit the growth of drug-resistant bacteria, including methicillin-resistant Staphylococcus aureus INA 00761 (MRSA) and vancomycin-resistant strain Leuconostoc mesenteroides VKPM B-4177 (VR) (VKPM–National Collection of Industrial Microorganisms (Russian acronym)).
Tworelated antibiotics, 167-A and 167-B, were isolated from the fermentation broth ofa mutant of an inactive wild strain of Amycolata autotrophica. Antibiotic 167-B was found to be cervinomycin A2; antibiotic 167-A is a new representative of the same group and has the structure of 18-O-demethyl cervinomycin A2.
Currently, the problem of antibiotic resistance of opportunistic and pathogenic microorganisms is extremely urgent. In order to find new effective natural antibiotics, it is necessary to intensify the search process. In the gradual selection of the most promising producers, we introduced the stage of determining the antibiotic activity of the culture fluid of the studied natural strains against the clinical isolates of hospital microorganisms with multiple resistance to medical antibiotics. Determining the species affiliation of potential producers allows to select those producers of a particular species that differ in the antimicrobial spectrum of activity from those described in the literature. Four strains of actinomycetes that showed activity against resistant clinical isolates of yeast Candida albicans, C.famata, C.parapsilosis and Cryptococcus neoformans were selected, namely: Nocardia soli INA 01217, Streptomyces bottropensis INA 01214, S.chromofuscus INA 01211 and S.netropsis INA 01190. The N.soli INA 01217 strain also shows antibiotic activity against the Gram-negative bacterium Escherichia coli ATCC 25922. These strains of actinobacterial producers were selected for subsequent chemical studies of the antimicrobial compounds formed by them.
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