This study investigated the impact of Methylococcus capsulatus, mixed with or without purified bacterial strains or mixed rumen fluid, on feeding grass-based and/or grain-based diet rations, as well as changes in bacterial cells, rumen fermentation rates, gas production, and rumen microbiota in in vitro and continuous culture. Three experiments were carried out using in vitro ANKUM gas production systems (Exp. 1 and 2) and continuous recirculating flux chamber systems (Exp. 3). In Exp. 1, four strains of rumen bacteria—Streptococcus bovis, Ruminococcus flavefaciens, Methanobrevibacter smithii, and Methylococcus capsulatus—were used to determine the effect of methane-utilizing bacteria (e.g., M. capsulatus) on specific growth rate, volatile fatty acid production, and ruminal methane emissions in co-culture with these bacterial strains. Results from Exp. 1 showed that M. smithii produced the most methane among the strains. When a combination of two microbes, including M. capsulatus, was used, no methane was detected, indicating that M. capsulatus could utilize most of the methane produced in mixtures with M. smithii and other ruminal bacterial strains. In the presence of M. capsulatus (Exp. 2), methane production decreased as the amount of M. capsulatus added increased. Using a continuous recirculating flux chamber system (Exp. 3), methane flux significantly reduced over time in both basal diets with M. capsulatus inoculum. Therefore, comparing methane-utilizing bacteria inoculation with current basal diets may reveal a biological pathway to mitigate methane production related to methanogenesis in ruminants.

Read the full article in the Journal of Animal Science.