Stable isotopes provide evidence that condensed tannins from sericea lespedeza are degraded by ruminal microbes

Abstract

The objective of Trial 1 was to determine the effects of condensed tannins (CT) from sericea lespedeza [SL; Lespedeza cuneata (Dum. Cours.) G. Don] on in vitro digestible organic matter (IVDOM), total gas production (GP), methane (CH4) emission, and ruminal fluid parameters after fermentation. Substrates used in four 48-h in vitro fermentations were 100% bermudagrass [(Cynodon dactylon (L.) Pers.] hay (0SL), 100% SL hay (100SL), and a mix of both hays (50SL). Linear reductions were observed for all parameters (P < 0.05) with the inclusion of SL, except for CH4 in relation to GP, that presented a quadratic effect (P = 0.005). In Trial 2, SL plants were enriched with 13C–CO2 to obtain pure enriched CT to identify the destination of fermentation end products of CT degradation. The enrichment of CT through the SL was successful (P < 0.001), and carbon originated from CT was detected in the fermentation end products [microbial mass, clarified rumen fluid, and in the CH4 produced (P < 0.001)]. Therefore, inclusion of SL was effective in reducing in vitro CH4 production and compound-specific tracing of δ13C abundance provided better quantitative understanding of the mechanisms of partitioning CT during ruminal fermentation processes.

Evolving understanding of rumen methanogen ecophysiology

“…Shotgun metagenome and metatranscriptome sequencing, and metaproteomic and metabolomic analyses, stable-isotope probing, as well as full genomes of the isolates, have made it possible to perform thorough and precise in situ assessments of the structures and metabolic functions of the rumen microbiome (Shi et al, 2014;Estes et al, 2018;Stewart et al, 2018;Shakya et al, 2019;Wilkinson et al, 2020;van Cleef et al, 2021van Cleef et al, , 2022. The recently developed technology to rapidly generate full genome sequences from metagenomic DNA samples, namely metagenome-assembled genomes or MAGs (Tyson et al, 2004;Almeida et al, 2019;Nayfach et al, 2019;Youngblut et al, 2020;Haryono et al, 2022) has been extended to studies on rumen microbiome (Solden et al, 2018;Stewart et al, 2018Stewart et al, , 2019Wilkinson et al, 2020;Xie et al, 2021) and it allows the assignment of potential metabolic capabilities and in situ roles to microbes that have not even been obtained in pure or enrichment cultures.…”