Isolation and functional study of efficient cellulose degrading bacteria from horse cecum contents

Objectives Animals that consume and digest roughage for a long time have unique gut microbiota in their gastrointestinal tract. Studying the isolation of beneficial functional bacteria from the gut can provide resources for the development of feed microbial additives. Therefore, the purpose of this study was to isolate and identify bacteria with cellulose degradation ability from the cecal contents of Yili horses, and to provide resources for the development of feed microbial additives. Methods Firstly, the cecal contents of 18 Yili horses were collected, and cellulose degrading bacteria were isolated and screened using CMC-Na screening medium under aerobic and anaerobic conditions. The strains with strong cellulose degradation ability were identified using Congo red staining and DNS methods. The top 60 strains with enzyme index were selected, and full-length 16S rRNA sequencing technology was used to identify and construct a phylogenetic tree. Select the top 5 strains of bacteria with high enzyme activity based on the measured cellulase activity, and the sheep were treated with mixed bacterial suspension by gavage. The rumen microbiota of sheep was analyzed using 16S rDNA amplicon sequencing technology. Results A total of 263 single colonies were isolated, of which 120 single colonies had a hydrolysis circle and colony enzymatic index (EI) of >1.5. Enzyme activity determination screening of the top 60 strains of full-length 16S rRNA sequencing, sequencing results show that the strains are mostly Bacillus spp. Among the 60 strains of bacteria, CE207 has the highest enzyme activity of 14.81 U/mL, and the lowest enzyme activity of CE105 is 1.91 U/mL. The mixed bacteria significantly increased the daily weight gain of sheep (P < 0.001) and feed intake (P < 0.001), and feed conversion rate increased from 7.75% to 10.09%. Sequencing results of sheep rumen microorganisms showed that, compared with the control group, the experimental group contained Muribaculum, Parvibacter, Desulfovibrio, Novosphingobium, Cutibacterium, Parasutterella, Lachnospiraceae_UCG-006, and Allobaculum genera increased significantly in abundance, and Fibrobacter and NK4A214_group genera decreased significantly in abundance, suggesting that a mixture of bacteria can influence the changes in the microflora of the rumen intestinal tract of sheep. Conclusions This finding suggests that the cellulose degrading bacteria isolated in the study can effectively promote the growth and development of herbivores such as sheep, and that efficient cellulose degrading bacteria in the animal gut may become a new direction for the development of feed additives in the future.