Taxonomic and functional characterization of the rumen microbiome of Japanese Black cattle revealed by 16S rRNA gene amplicon and metagenome shotgun sequencing

This study aimed to determine the taxonomic and functional characteristics of the Japanese Black (JB) steer rumen microbiome. The rumen microbiomes of six JB steers (age 14.7 [+ or -] 1.44 months) and six JB sires x Holstein dams crossbred (F1) steers (age 11.1 [+ or -] 0.39 months), fed the same diet, were evaluated. Based on 16S rRNA gene sequencing, the beta diversity revealed differences in microbial community structures between the JB and Fl rumen. Shotgun sequencing showed that Fibrobacter succinogenes and two Ruminococcus spp., which are related to cellulose degradation were relatively more abundant in the JB steer rumen than in the Fl rumen. Furthermore, the 16S rRNA gene copy number of F. succinogenes was significantly higher in the JB steer rumen than in the Fl rumen according to quantitative real-time polymerase chain reaction analysis. Genes encoding the enzymes that accelerate cellulose degradation and those associated with hemicellulose degradation were enriched in the JB steer rumen. Although Preuotelk spp. were predominant both in the JB and Fl rumen, the genes encoding carbohydrate-active enzymes of Preuotelk spp. may differ between JB and Fl. Keywords: carbohydrate-active enzyme; early fattening stage; fibrolytic bacteria; Japanese Black cattle; metagenomics; rumen microbiome