A small scale rumen incubation system to screen chemical libraries for potential methane inhibitors

There is currently an urgent need for effective anti-methanogen small molecule inhibitors to help control ruminant methane emissions on a global scale. No assays system has yet been reported that would enable high-throughput screening of either rumen methanogen cultures or an assay system that utilizes rumen fluid. We report here the development of a high-throughput 1.2 ml rumen fluid-based 96-well screening system that incorporates an easily measured substrate for growth with a short incubation time that is combined with an automated gas chromatography injection system for gas analyses. The system markedly enhances the number of samples that can be processed (~1000 per week) compared to previously published assays. We also assessed the system using known rumen anti-methanogen inhibitory compounds, a set of anthraquinone derivatives and 3-nitrooxypropanol. The assay system can detect inhibitors that are methanogen-specific and discriminate between molecules that act as methanogen inhibitors and those acting as electron sinks.