Features of associative symbiosis on the example of intestinal bacterioflora of rainbow trout (Parasalmo mykiss walbaum)

The features of associative symbiosis were studied on the example of intestinal bacterioflora of three age groups of rainbow trout grown in conditions of cage culture in the waters of Lake Ladoga. Methods of microbiological analysis and Sanger genome-wide sequencing were used to describe the structure of associative symbiosis of trout intestine. To identify the significance of various bacterial taxa in associative symbiosis, a series of experiments on co-culture and evaluation of the viability of associates were performed. As a result of microbiological analysis and genotyping, 310 bacterial species belonging to 37 genera were described. Due to a comparative study of the composition of the intestinal microflora, it was found that firmicut bacteria dominated in the age group 1+, and proteobacteria dominated in the age groups 2+ and 3+. Representatives of 11 genera were classified as constant taxa, for which a sequential change of dominant, subdominant and minor microsymbionts was described, depending on the age group of trout. For the age group 1+ the priority of taxon changes consisted of the sequence of Eubacterium Bacteroides Micrococcus Proteus Fusobacterium, for the age group 2+ the sequence was: Bacillus Propionibacterium Bacteroides Fusobacterium Citrobacter, and for the age group 3+ the sequence was: Bacillus Proteus Flexibacter Campylobacter Cetobacterium. As a result of an experiment on the co-culture of intestinal bacterioflora of one-year-old and two-year-old trout individuals, a mutually stimulating effect between the associates was described. This is evidenced by the high values of the optical density of the culture solution, the long-term linear growth, the constancy of the rate of biomass accumulation and the achievement of a large number of viable cells in the association.