Improved culturability of cellulolytic rumen bacteria and phylogenetic diversity of culturable cellulolytic and xylanolytic bacteria newly isolated from the bovine rumen

Abstract

The phylotypes of rumen bacteria have increased by the accumulation of 16S rRNA gene sequences, and they show a complex microbial community structure in the rumen. However, most of the biochemical properties of rumen bacteria defined by phylotypes are still unknown. We attempted to improve the culturability of cellulolytic bacteria from the rumen using an agar medium (CA) and a gellan gum medium (CG) containing azo-carboxymethylcellulose as a carbon source. We isolated 129 strains from these media, and the numbers of isolates that showed filter paperase, carboxymethylcellulase and xylanase activity were 51, 117 and 105, respectively. The isolates were classified into six phyla by 16S rRNA gene sequences. In accordance with other studies, fibre-adherent rumen bacteria from the phylum Firmicutes were the most abundant cultured isolates obtained (82.2%). Isolates that were unclassified (< 97% similarity) totalled 19.4%, indicating that the media used in this study was successfully able to improve the culturability of rumen cellulolytic bacteria. Moreover, as the Chao1 richness of CG was higher than that of CA, we estimated that, compared with CA, CG supports the growth of a wide variety of rumen bacteria. These results demonstrate that culturable species of ruminal cellulolytic bacteria can be increased using improved culture media.