Lactobacillus casei and Lactobacillus rhamnosus proteins P40 and P75 belong to a large family of secreted cell wall proteins that contain a carboxy(C)-terminal CHAP or NlpC/P60 superfamily domains. In addition to their peptidoglycan hydrolases activity, proteins in this family are specific antigens of pathogens, frequently responsible of interactions with the host. L. rhamnosus GG and L. casei BL23 purified P40 and P75 proteins have antiapoptotic activity by inducing the EGF/Akt pathway. The aim of this work was to study the genetics, phylogeny and dissemination of this family of proteins in the genus Lactobacillus as well as their characteristics and likely function. The scrutiny of their DNA encoding sequences revealed the presence of minisatellite DNA in the P75 encoding gene of L. casei/paracasei strains ( cmu B) with intraspecific indels that gave raise to four different alleles ( cmu B1–4), which are exclusive of this species. Phylogenic analyses suggest that both proteins are present mainly in the L. casei and Lactobacillus sakei phylogenomic groups. A P40 ancestral gene was possibly present in the common ancestor of Enterococcaceae , Lactobacillaceae and Streptococcaceae . P75 is also present in L. casei and L. sakei groups, but its evolution is difficult to explain only by vertical transmission. Antibodies raised against the N-terminal regions of P40 and P75 improved their immunological detection in culture supernatants as they recognized almost exclusively proteins of L. casei/paracasei/rhamnosus strains, highlighting their structural similarity, that allowed to detect them in different fermented dairy products that contained probiotic L. casei strains. Purified P40 and P75 proteins showed no evident lytic activity but they complemented L. casei BL23 cmu A and cmu B defective mutants, respectively, thus proving that they actively participate in cell division.

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Currently, in Kazakhstan, chemical agents and antibiotics are widely used for treatment and prevention of fish diseases at fish farms. The use of probiotics as an alternative to antibiotics can help reduce the spread of antibiotic resistance in this area. The aim of the present study was to isolate the intestinal lactic acid bacteria of wintering carps. We assume that such bacteria can have more adaptive properties and can be used as probiotics for growing carp juveniles at fish farms. A probiotic characteristic of 22 lactic acid bacteria isolated from Common carp intestines was studied. Universal primers were used to determine the sequence of 16S rRNA gene fragments of lactic acid bacteria (LAB). Phylogenetic relationships of the isolates were estimated using the neighbor-joining (NJ) method in Mega 6,0. All identified isolates can grow in temperature range from 10° C to 37° C and in presence of bile salt. The isolated bacteria were screened for antibacterial activity, resistance to bile, resistance to antibiotics and growth at low temperatures. All isolates were tested in vitro for their ability to inhibit the growth of Shewanella xiamenensis, Pseudomonas taiwanensis, Ps. aeruginosa and Aeromonas punctata. As a result, 7 isolates with strong antagonistic activity were selected. 16S rDNA gene sequencing identified 4 isolates as Lactobacillus fermentum, 2 - as L. casei/paracasei and 1 - as Pediococcus pentosaceus. Antibiotic resistance profile of selected strains was studied, too. This study is the first attempt for Kazakhstan to isolate and study the representatives of the normal intestinal microflora of commercial fish species. Selective strains could be potential probiotics for freshwater aquaculture practices in Kazakhstan.

Объекты исследования – молочнокислые бактерии (МКБ), выделенные из биологических образцов, и коллекционные штаммы МКБ. Цель – характеристика штаммов пробиотиков для разработки напитков профилактического назначения. В процессе работыпроведен скрининг пробиотически активных штаммов МКБ, в результате которого отобрано 17 наиболее активных культур, среди которых 13 коллекционных штаммов из Биобанка промышленных микроорганизмов Республиканской коллекции микроорганизмов и 4 лабораторных изолята. Изучен пробиотический потенциал бактерий: продукция молочной кислоты, антагонизм к условно-патогенным микроорганизмам, адгезивные свойства, устойчивость к неблагоприятным условиям желудочно-кишечного тракта (ЖКТ). Идентификация с использованием системы Bruker MALDI-TOF Biotyper позволила отнести изоляты к следующим видам: Lactobacillus casei, Lactobacillus paracasei, Lactobacillus plantarum. В результате проведенных исследований созданы консорциумы стартерных культур из штаммов Lactobacillus paracasei 2А, Lactobacillus casei Y1, Lactobacillus plantarum 1А, Lactobacillus plantarum 17 А, Lactobacillus brevis 4 LB B-RKM 0610 и отобран оптимальный вариант, соответствующий основным технологическим характеристикам с учетом биосовместимости штаммов для включения в состав разрабатываемого напитка профилактического назначения. The objects of study are lactic acid bacteria (LAB) isolated from biological samples and collection strains of LAB Purpose - characterization of probiotic strains for the development of preventive drinks In the course of the work, screening of probiotically active strains was carried out, as a result of which 17 cultures were selected as the most active, among them 13 collection strains from the Biobank of Industrial Microorganisms of the Republican Collection of Microorganisms and 4 laboratory isolates. The probiotic potential was studied, among which, the production of lactic acid, antagonism to opportunistic microorganisms, adhesive properties, resistance to adverse conditions of the gastrointestinal tract. Identification using the Bruker MALDI-TOF Biotyper system allowed isolates to be assigned to the following species: Lactobacillus casei, Lactobacillus paracasei, Lactobacillus plantarum. As a result of the research, consortiums of starter cultures were created from strains of Lactobacillus paracasei2A, Lactobacillus casei Y1, Lactobacillus plantarum 1A, Lactobacillus plantarum 17 A, Lactobacillus brevis 4 LB B-RKM 0610 and the optimal variant was selected that corresponds to the main technological characteristics, taking into account the biocompatibility of strains for inclusion in the composition of the drink for preventive purposes.