Isolation and characterization of tannin-degrading bacteria from the rumen of wild Hokkaido sika deer (Cervus nippon yezoensis)

We isolated tannin-degrading bacteria from the rumen of wild Hokkaido sika deer and characterized their phylogeny and tannase activity in relation to sample sources. The condensed tannin level was higher in all deer rumen samples (n = 20) than in forage-fed cattle rumen samples (n = 6), whereas no hydrolyzable tannins were detected in any of the rumen samples. Rumen bacteria were enumerated on nonselective brain heart infusion (BHI) agar medium and then transferred onto tannic acid-containing BHI agar plates to screen for bacteria only showing growth (tannin-resistant bacteria) and those showing both growth and a clear zone (tannin-degrading bacteria). Summer samples provided only tannin-resistant bacteria, none of which showed tannin-degrading activity. Although winter samples also provided tannin-resistant bacteria, most isolates exhibited tannin-degrading activity. A total of 70 isolates exhibiting tannin-degrading activity were classified as Streptococcus bovis group based on 16S rRNA gene sequencing and further classified into two groups, either group A or group B. Group A consisted of isolates showing weak tannase activity, whereas group B included a majority of the isolates exhibiting high tannase activity. These results suggest that wild Hokkaido sika deer develop tannin-degrading Streptococcus in the rumen during winter, which allows access to woody food materials rich in tannins.