Effect of Bacillus subtilis on the rumen microbial community and its components exhibiting high correlation coefficients with the host nutrition, growth, and development

T-RFLP investigation of the microbial community of the ruminal fluid of calves revealed changes in the microbiocenosis resulting from feeding the animals with biofilm-protected Bacillus subtilis cells. In the control animals, which switched from the diary to the vegetable diet, the phylum Firmicutes predominated Firmicutes (55.11 ± 1.97%), in particular the class Clostridia (53.10 ± 2.06%), families Lachnospiraceae (25.93 ± 1.41%) and Clostridiaceae (9.90 ± 1.35%). Members of the phyla Bacteroidetes (11.15 ± 2.88%) and Actinobacteria (9.27 ± 1.95%) were also present. Uncultured forms constituted 17.28 ± 2.01%. The share of bacilli (family Bacillaceae) was below 2% (1.46 ± 0.41%). Introduction of B. subtilis cells into the rumen of experimental animals increased the share of Bacillaceae to 2.80 ± 0.30%. The numbers of Thermoanaerobacteriaceae, Peptostreptococcaceae, and Alicyclobacillaceae increased by an order of magnitude. The numbers of Pseudomonadaceae, Burkholderiaceae, and uncultured Bacteroidetes increased twofold. Increased numbers of the rumen bacteria and protozoa, elevated fatty acid content, and higher ammonia emission indicated increased efficiency of digestion. Some families, including the domineering ones, included the members with different directions of the correlation with the indices of rumen digestion. The introduced bacilli stimulated the phylotypes with the positive correlation coefficients and suppressed those with the negative correlation. This, the rumen ecosystem was modified in the direction of improved digestion. The functional role of the members of the microbial community, for which the correlations were negative, weakly associated, or unassociated with the indices of rumen digestion are discussed.