В настоящее время происходит бурный рост и развитие отечественного кормопроизводства, появляются новые рецептуры комбинированных кормов. В связи с этим растет необходимость в качественной оценке эффективности различных добавок, входящих в состав этих кормов, и для этого необходима надежная модель для оценки состояния рыбы. Проанализировано изменение морфологических и физиологических признаков, а также состояния микробиома у стерляди, потреблявшей корма различного качества, для определения физиологических показателей, наиболее подверженных влиянию состава пищи. Стерлядь, получавшая корм ненадлежащего качества, в среднем обладала на 7 % меньшей конечной массой, кровь рыб характеризовалась значительным падением уровня триглицеридов и β-липопротеидов в конце эксперимента. Результаты анализа кишечного микробиома показали, что у стерляди, получавшей некачественный корм, в кишечнике увеличивалось количество Enterococcus и актиномицетов, а также появлялось значительное количество представителей лактозоположительных бактерий, которые отсутствовали у особей из контрольной группы. Кроме того, у рыб, получавших некачественный корм, но остававшихся в хорошем физиологическом состоянии, в кишечнике были обнаружены бактерии Bacillus , отсутствовавшие у других групп, что может говорить о потенциальной пробиотической активности бактерий рода Bacillus, выделенных из их микробиома.

Fusarium diseases cause serious damage to agricultural crops. In agricultural practice, various chemical fungicides, usually based on triazole, are often used to control fusariosis. This leads to the emergence of resistant forms among pathogenic fungi. An alternative to chemical fungicides treatments may be the use of biopreparations based on natural antagonists of Fusarium . Bacillus and Paenibacillus bacteria isolated from farmland soils exhibit a high level of antagonism against phytopathogenic fungi of the genus Fusarium . PCR-based analysis revealed that genes of non-ribosomal peptide synthases are present in the genomes of isolated bacterial strains, while these strains do not have any chitinase activity, so the antifungal effect seems to be provided predominantly by non-ribosomally synthesized peptides. The expression of the detected genes is increased in the presence of fungi during co-culturing, and this effect is strain-specific and pathogen-dependent. In light of these findings, the development of pathogen-specific drugs seems promising.### Competing Interest StatementThe authors have declared no competing interest.

Members of the genus Enterococcus are common gut symbiotic organisms that meet all the requirements for probiotics. In our study, the biological activity of individual fractions of metabolites excreted by probiotic bacteria of 3 strains of Enterococcus durans was studied using biosensor testing. Biosensor testing was performed using two biosensor strains (Escherichia coli MG1655 pRecA-lux and Escherichia coli MG1655 pKat-lux) and three inducers (hydrogen peroxide, dioxidin, ciprofloxacin). The study showed that the probiotic action of E. durans was associated with the activity of individual fractions of bacterial metabolites. Moreover, different fractions exhibited different profiles of biological activity. It has also been demonstrated that the metabolites of these strains can not only demonstrate protective activity but also induce DNA damage. These criteria should be considered in the initial screening of potential probiotic strains to avoid possible adverse effects.

The initial screening of probiotic strains in vitro, carried out by different methods, may omit strains that are promising from the point of view of biotechnology or, conversely, mark as promising strains those that will lose activity when transferred in vivo. It is known that the release of metabolites by probiotic bacteria, in particular, lactobacilli, is highly dependent on the biochemical context. In this work, we modified the method that was previously successfully used for the selection of probiotics for poultry, based on their antioxidant and DNA-protective properties. A comparison was made of this activity on standard media and on an artificial intesti-nal medium that mimics the intestines of a bird. As a result, three Lactobacillus strains were selected, which not only exhibit antioxidant and DNA-protective properties but also do not lose these activities in an artificial in-testinal medium.