Transcriptome response of Methanobrevibacter ruminantium to lauric acid in cell culture.

Medium chain fatty acids (MCFA) have been shown to inhibit methanogenesis, disrupt the cell envelope, and decrease survival of Methanobrevibacter ruminantium M1 in a dose-, time-, and protonation level dependent way. However, the exact mechanisms behind these observations are still unknown. Although the biochemistry of the metabolic processes of M. ruminantium has been well studied and its genome sequence is now available, little is known about the overall transcriptome regulation of M. ruminantium in response to inhibitors like MCFA. In the present study, we used RNA Sequencing to evaluate the effects of lauric acid (C12) on M. ruminantium. Pure M. ruminantium cell cultures in the mid-exponential growth phase were exposed to C12 in concentrations of 0.4 mg/mL, dissolved in DMSO for 1 h, and the transcriptomic changes compared to DMSO-only treated control samples (final DMSO concentration 0.2 %), were investigated. Gene expression changes upon exposure to C12 were not dramatic in magnitude (log2 fold change mostly below +/- 3) and in gene number (214 genes). However, the observed expression changes affected mostly genes which encoded cell-surface associated proteins (adhesion-like proteins, membrane-associated transporters and hydrogenases), or proteins, which were involved in detoxification or DNA repair processes. The transcriptional response of M. ruminantium M1 to C12 did not specifically inhibit methanogenesis. Instead, the data indicated a non-specific antimicrobial action by lauric acid, which involves destruction of the cell membrane and interferences with cellular energetics in M. ruminantium. To date, there has been no systematic characterization of a ruminal methanogen transcriptome by deep sequencing. Our results give first hints on the molecular inhibitory mechanism of C12 on M. ruminantium.