Inhibitory effects of saturated fatty acids on methane production by methanogenic <i>Archaea</i>

The Effect of Saturated Fatty Acids on Methanogenesis and Cell Viability ofMethanobrevibacter ruminantium

“…Although cell inoculum each time was always applied by transferring the same volume using the microbes at almost the same growth phase and the cell suspensions were prepared by following the same protocol in each incubation, it seems that cell susceptibility varied between incubations, which also caused variability in the CH 4 production patterns of the control groups (Figure 1 and Supplementary Figure 1). In agreement with studies performed at 35–38°C and neutral pH in cultures of ruminal and nonruminal methanogens and bacteria [12, 13, 32] and in sheep in vivo [33], the present data also indicate that C 12 and C 14 are the most effective SFAs. C 12 had also been the most inhibitory representative of the SFAs against 12 Gram-positive microorganisms [32].…”

“…This might have resulted either from the difference in metabolic state between cell cultures and cell suspensions or from differences in growth states before SFA supplementation and harvesting or both. Still, the SFA concentrations where a significant inhibition of methanogenesis occurred in the present study (10 to 80  μ g/mL) were in the same order of magnitude than those reported earlier (30 to 1000  μ g/mL) in growing methanogen cultures [12, 13, 20, 32]. This indicates that in cell cultures and cell suspensions generally the same type of effect occurs.…”

“…C 18 was only inhibitory at 50°C, which corresponds with its increased solubility at this temperature. This supports the hypothesis that SFAs need to be at least partly dissolved in the buffer or medium to be able to exert an effect [13]. Further experiments have to investigate if the SFAs state (protonated versus dissociated) plays a role in M. ruminantium .…”

“…The production of CH 4 by pure, growing, cultures of M. ruminantium , a dominant ruminal methanogen [3], was found to be inhibited by the addition of unsaturated [11, 12] and saturated medium-chain (C 12 –C 16 ; [12]) fatty acids. When testing the nonruminal methanogens Methanothermobacter thermoautotrophicus and Methanococcus voltae , C 12 and C 14 were found to inhibit methanogenesis as well [13]. However, systematic studies on dose-response relationships with SFAs on methanogenesis in pure ruminal methanogen cultures are missing.…”

“…However, systematic studies on dose-response relationships with SFAs on methanogenesis in pure ruminal methanogen cultures are missing. Besides, it is unclear why long-chain SFAs do not inhibit methanogenesis and if this is related to the low solubility of these long-chain SFAs at temperatures below 40°C [13, 14]. Furthermore, although fatty acids (FAs) are known to have antimicrobial and cytotoxic properties [15] and are used by a wide range of organisms like humans [16], molluscs [17], and brown algae [18] to defend against pathogens, the mechanisms which lead to the inhibition effect are still not definitely known.…”