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Aim: Selection of high-mucoid morphotype of Streptococcus equi subsp. zooepidemicus (Streptococcus zooepidemicus) and study of its morphological, physiological, biochemical and technological characteristics for providing increased secretion of hyaluronic acid (HA)., Materials and Methods: Submerged cultivation was performed in 100 ml glass flasks without baffles or in 1.5 or 10 1 laboratory bioreactors. LB and MRS media were used for cultivation. Mutagenesis was carried out by UV exposure with consequent selection of mucoid phenotype. HA was determined by carbazole method or after exhaustive acid hydrolysis by reaction of N-acetylglucosamine with Morgan-Elson reagent. Total hyaluronidase activity was evaluated by viscosimeter. Determination of cell and capsule size, ability to ferment carbohydrates and other microbiological, physiological and biochemical tests were performed by standard techniques., Results: Instability of capsule phenotype of S. zooepidemicus B-8014 strain was revealed that is explained most probably by formation under certain conditions of bacterial hyaluronidase. This is confirmed by a reduction of HA concentration in cultural medium at pre- and stationary growth phases. Mucoid strain S. zooepidemicus KB-04 was obtained by mutagenesis with subsequent selection that is characterized by increased capsules. The strain was studied for HA formation. Optimization of growth medium composition, physical-chemical conditions and modes of cultivation allowed to significantly increase HA yield., Conclusion: The studies of morphologic, physiologic, biochemical and technological characteristics of the high-mucoid S. zooepidemicus KB-04 strain obtained by mutagenesis with consequent selection were performed, conditions of its cultivation and composition of growth mediu by carbon source and content of bivalent metal ions were optimized.

Bacteriocin production in many Gram-positive bacteria is controlled by a two-component regulatory system that is composed of the sensor protein and the response regulator. In this work, methods of computer analysis were used to describe the locus of genes responsible for the synthesis of class II bacteriocins in the Streptococcus equi genome. Potential regulatory sites (direct repeats) recognized by a DNA-binding protein of the corresponding two-component system were predicted.