Condensed tannin (CT) fractions of different molecular weights (MWs) may affect the rumen microbial metabolism by altering bacterial diversity. In this study, the effects of unfractionated CTs (F0) and five CT fractions (F1-F5) of different MWs (F1=1265.8 Da, F2=1,028.6 Da, F3=652.2 Da, F4=562.2 Da and F5=469.6 Da) from Leucaena leucocephala hybrid-Rendang (LLR) on the structure and diversity of the rumen bacterial community were investigated in vitro.
Real-time PCR assay showed that the total bacterial population was not significantly (P > 0.05) different among the dietary treatments. Inclusion of higher-MW CT fractions F1 and F2 significantly (P < 0.05) increased the Fibrobacter succinogens population compared to F0 and CT fractions F3-F5. Although inclusion of F0 and CT fractions (F1-F5) significantly (P < 0.05) decreased the Ruminococcus flavefaciens population, there was no effect on the R. albus population when compared to the control (without CTs). High-throughput sequencing of the V3 region of 16S rRNA showed that the relative abundance of genera Prevotella and unclassified Clostridiales significantly (P < 0.05) decreased, corresponding with increasing MWs of CT fractions, whereas the cellulolytic bacteria of the genus Fibrobacter was significantly (P < 0.05) increased. Inclusion of higher-MW CT fractions F1 and/or F2 decreased the relative abundance of minor genera such as Ruminococcus, Streptococcus, Clostridium XIVa, and Anaeroplasma, but increased the relative abundance of Acinetobacter, Treponema, Selenomonas, Succiniclasticum, and unclassified Spirochaetales compared to the control and lower-MWs CT fractions.
This study indicates that CT fractions of different MWs may play an important role in altering the structure and diversity of the rumen bacterial community in vitro, and the impact was more pronounced for CT fractions with higher MW.