Comparative analysis of rumen bacterial community of young and adult Rangifer tarandus reindeers from arctic regions of Russia in the summer-autumn period

Reindeer husbandry is a strategically important industry in the Arctic regions of Russian Federation due to providing the native population with food stuffs. Observing the characteristics of rumen microorganisms' composition is necessary to deepen the information on the reindeer physiology. In this paper, the results of molecular genetic analysis of the rumen bacterial community composition of young and adult specimen Rangifer tarandus individuals from Arctic regions of Russia are presented for the first time. Samples of ruminal contents were collected from 3 animals of each age group in 2017 summer-autumn period in the Yamal-Nenets Autonomous District and the Murmansk Province. The bacterial community composition of the reindeer rumen was analyzed in the laboratory of the «BIOTROF+» company by T-RFLP method (terminal restriction fragment length polymorphism). According to the biodiversity indicators, the Yamal-Nenets Autonomous District reindeer ruminal microorganisms' diversity was significantly higher (P < 0.05) than that in the reindeers of Murmansk region. Young reindeers from the Yamalo-Nenets Autonomous District showed lower biodiversity indicators (P < 0.05) comparing to adults, whereas in the Murmansk region this was not observed. According to the taxonomic affiliation, it has been established that up to 83.50±5.07 % of the phylotypes belong to four bacterial phylums, the Firmicutes, Bacteroidetes, Actinobacteria and Proteobacteria, while Tenericutes, Fusobacteria, Acidobacteria, Cyanobacteria were less frequent. Ruminal microbiome of Rangifer tarandus reindeers showed much higher proportion of unidentified bacteria, as well as the Eubacteriaceae and Clostridiaceae bacteria, as compared to the most studied members of the Bovidae family. Note, that several Eubacteriaceae and Clostridiaceae members are capable of detoxification of usnic acid and other secondary metabolites produced by lichens. During the reindeer ontogenesis, noticeable changes in the ratio of phylotypes and taxonomic groups in rumen microbiota were found. The greatest age changes were noticed in the phylum Firmicutes composition. In adult reindeer rumen, the total counts of cellulosolytic bacteria of the Clostridia class, especially of the families Eubacteriaceae, Clostridiaceae and Lachnospiraceae potentially capable of hydrolysis of plant carbohydrates with the formation of volatile fatty acids (VFA), were significantly higher than in young group (P < 0.05). The inverse pattern was characteristic of bacteria with similar properties from the phylum Bacteroidetes, including the genera Bacteroides, Prevotella. Identification of a significant number of opportunistic and pathogenic microorganisms in the Rangifer tarandus rumen bacterial community, with the dominance of the phylum Fusobacteria, families Сampylobacteriaceae and Enterobacteriaceae, is also of interest. Up to date, this issue has been poorly observed. Direct regularity in changing ruminal pathogen profiles in reindeers of different age or from different habitat was not revealed. Perhaps the detected differences in the level of pathogenic and opportunistic microorganisms could be associated with other factors, e.g. specific pasture ration in different regions or the epizootic situation in the herd. Additional research will clarify the issues in question. In general, the obtained results can be used as a basis to develop recommendations for improving the efficiency of animals breeding.