Characterization and identification of cellulase-producing Enterococcus species isolated from Tibetan yak (Bos grunniens) rumen and their application in various forage silages.

Abstract

Cellulase-producing Enterococcus species isolated from the rumen of Tibetan yak (Bos grunniens) were characterized, and their combined effects on the silage quality of various forages were studied. The two isolated strains with high cellulolytic potential were identified as Enterococcus faecalis (EF85) and E. faecium (EF83) by 16S rRNA sequencing. Both EF85 and EF83 could grow well at 15-55°C, pH 3·0-6·0 and in 3·0-6·5% NaCl. The cellulase secreted by EF85 and EF83 showed good stability at temperatures from 20 to 45°C and pH from 4·5 to 7·0. A commercial inoculant (CLP), a commercial cellulase (CE) and the two cellulolytic strains (EF85+EF83) were added to whole-crop corn, sweet sorghum and Napier grass ensiling for 120days respectively. In Napier grass silage, all inoculants significantly increased lactic acid content and ratio of lactic to acetic acid and decreased pH, butyric acid and ammonia nitrogen contents. The acid detergent fibre and cellulose contents in EF85+EF83 treatment were significantly lower than those in the other treatments. In whole-crop corn and sweet sorghum silages, all additives had no significant effect on the fermentation quality, while CE and EF85+EF83 markedly enhanced cellulose degradation and increased free sugar content. The combined inoculation of the cellulolytic strain EF85 and EF83 to various forages reduced the fibre content of the resulting silages. Few studies involved inoculation of silage with Enterococcus species in different forage types. The isolated cellulolytic strains of E. faecalis EF85 and E. faecium EF83 could be a great alternative for commercial inoculants and enzymes in silage production.