Violacein is a biotechnologically significant secondary metabolite due to its antibacterial, antifungal, and other properties. Isolation, research, and identification of violacein producing strains are of interest for the development of biotechnological processes, in order to enhance the biosynthesis of this compound. The purpose of the present work was to study the properties of a newly isolated bacterium capable of synthesizing blue-purple pigment. An aboriginal bacterium was isolated from the coastal zone of the Vezelka River in the city of Belgorod. Based on chemical and spectrophotometric studies of the crude ethanol extract, the pigment was identified as violacein, and the isolate was assigned to the group of violacein-forming bacteria, which includes bacteria of the genera Chromobacterium, Iodobacter, Janthinobacterium, Duganella, Collimonas, and Massilia. Based on cultural, morphological, tinctorial, physiological, and biochemical properties, as well as analysis of the 16S rRNA gene sequence, the new isolated strain was assigned to the genus Janthinobacterium. The isolated strain is capable of suppressing the growth of a number of fungal and bacterial phytopathogens. For representatives of the genus Janthinobacterium, their inhibitory influence on cyanobacteria was shown for the first time.

Bacteria, designated as A1.1 and A1.2, were isolated from poultry waste based on the ability to form ammonia on LB nutrient medium. Whole genome sequencing identified the studied strains as Peribacillus frigoritolerans VKM B-3700D (A1.1) and Bacillus subtilis VKM B-3701D (A1.2) with genome sizes of 5462638 and 4158287 bp, respectively. In the genome of B. subtilis VKM B-3701D, gene clusters of secondary metabolites of bacillin, subtilisin, bacilisin, surfactin, bacilliacin, fengycin, sactipeptide, and ratipeptide (spore killing factor) with potential antimicrobial activity were identified. Clusters of coronimine and peninodin production genes were found in P. frigoritolerans VKM B-3700D. Information on coronimine in bacteria is extremely limited. The study of the individual properties of the strains showed that the cultures are capable of biosynthesis of a number of enzymes, including amylases. The B. subtilis VKM V-3701D inhibited the growth of bacterial test cultures and reduced the growth rate of the mold fungus Aspergillus unguis VKM F-1754 by 70% relative to the control. The antimicrobial activity of P. frigoritolerans VKM V-3700D was insignificant. At the same time, a mixture of cultures P. frigoritolerans VKM B-3700D/B. subtilis VKM B-3701D reduced the growth rate of A. unguis VKM F-1754 by 24.5%. It has been shown that strain A1.1 is able to use nitrogen compounds for assimilation processes. It can be assumed that P. frigoritolerans VKM V-3700D belongs to the group of nitrifying or denitrifying microorganisms, which may be important in developing methods for reducing nitrogen load and eutrophication.

Clavibacter michiganensis causes plant diseases and is included in the list of microorganisms subject to export control. Janthinobacterium lividum is capable of synthesizing a pigment with antagonistic potential. The purpose of the study was to evaluate the activity of J. lividum VKM B-3705D and the pigment fraction against C. michiganensis VKM Ac-1402. The results of spectrophotometric and nuclear magnetic resonance analysis showed that the pigment synthesized by the J. lividum VKM B-3705D corresponds to violacein. The J. lividum strain demonstrated potential bacteriostatic activity against C. michiganensis VKM Ac-1402 when both strains were co-cultured. Compared to the control (DMSO), the violacein solution suppressed the specific growth of Clavibacter by 57.7%. The mechanism of suppression of the growth of Clavibacter is discussed. One of the ways to suppress the growth of C. michiganensis may be the inhibition of key enzymes. Violacein inhibited the activity of adenosine triphosphatase (ATPase, EC 3.6.1.3) compared to the control (DMSO) by 23.2%. Thus, the current study of the bacteriostatic effect may be a decisive step towards the development of a plant protection product.

The paper presents a study of the antifungal activity of the pigment-forming strains Janthinobacterium lividum VKM B-3515, Pseudomonas chlororaphis VKM B-3546D and their mixture against the test culture Aspergillus unguis VKM F-1754. The growth rate of the colony and the average growth of A. unguis VKM F-1754 in the presence of J. lividum VKM B-3515 were 46.3% lower than the control variant. The growth rate of fungi in the presence of a mixture of two bacteria was 32% lower than in the control, and in the variant with a pure culture of Pseudomonas, it was 21%. The average increase in the diameter of the colonies of A. unguis VKM F-1754 cultivated with (P. chlororaphis VKM B-3546D-J. lividum VKM B-3515) was 33% lower than the control variant with Pseudomonas. While the mixture (P. chlororaphis VKM B-3546D-J. lividum VKM B-3515) showed less activity compared to the pure culture of J. lividum VKM B-3515. Thus, the use of two strains together may not be appropriate.

The study presents growth kinetics of a BG28 bacterial strain isolated from vermicompost (generated with the use of Eisenia fetida worms). The strain was given a codename BG28. It was revealed that the isolate is capable of using high concentrations of sodium benzoate (up to 15 g/l) as a substrate. At the same time, the rate and division constants of a culture that grows at 5 g/l, 10 g/l, and 15 g/l do not differ. However, the mean and specific increment of BG28 at the end of the logarithmic growth phase is significantly higher in the variant with 5 g/l. It was testified, that with the shortest duration of the logarithmic growth phase on a medium with 5 g/l, the substrate loss constant is higher than in other variants. The difference in the kinetic parameters of the culture at 5 g/l and 10 g/l sodium benzoate is insignificant. With an increase of the substrate concentration to 15 g/l, the duration of the logarithmic growth phase increased significantly, but the sodium benzoate decrease constant was found to be the lowest. During the study of the individual properties of BG28, it was revealed that the strain is capable of growing on benzoic acid. On this basis, it can be assumed that the culture contributes to the degradation of plant residues during vermicomposting. Besides, the isolate grows on a mineral nutrient medium with polyethylene glycol 6000 and liquid paraffin. In the process of the individual properties estimation, it was revealed that the strain is capable of local suppression of the Alternaria brassicicola VKM F-1864 mold growth when co-cultivated on agar nutrient medium.

This study describes the biotechnological significance of the by-product obtained in the production of milk products in the food industry.