Activity and Viability of Methanogens in Anaerobic Digestion of Unsaturated and Saturated Long-Chain Fatty Acids

Abstract

bLipids can be anaerobically digested to methane, but methanogens are often considered to be highly sensitive to the long-chain fatty acids (LCFA) deriving from lipids hydrolysis. In this study, the effect of unsaturated (oleate [C 18:1 ]) and saturated (stearate [C 18:0 ] and palmitate [C 16:0 ]) LCFA toward methanogenic archaea was studied in batch enrichments and in pure cultures. Overall, oleate had a more stringent effect on methanogens than saturated LCFA, and the degree of tolerance to LCFA was different among distinct species of methanogens. Methanobacterium formicicum was able to grow in both oleate-and palmitate-degrading enrichments (OM and PM cultures, respectively), whereas Methanospirillum hungatei only survived in a PM culture. The two acetoclastic methanogens tested, Methanosarcina mazei and Methanosaeta concilii, could be detected in both enrichment cultures, with better survival in PM cultures than in OM cultures. Viability tests using live/dead staining further confirmed that exponential growth-phase cultures of M. hungatei are more sensitive to oleate than are M. formicicum cultures; exposure to 0.5 mM oleate damaged 99% ؎ 1% of the cell membranes of M. hungatei and 53% ؎ 10% of the cell membranes of M. formicicum. In terms of methanogenic activity, M. hungatei was inhibited for 50% by 0.3, 0.4, and 1 mM oleate, stearate, and palmitate, respectively. M. formicicum was more resilient, since 1 mM oleate and >4 mM stearate or palmitate was needed to cause 50% inhibition on methanogenic activity.A naerobic degradation of long-chain fatty acids (LCFA) is essential for efficient biogas production from complex lipidcontaining wastewaters (1-3). However, there is still concern regarding the potential toxic effect of LCFA toward methanogenic communities. Toxicity of LCFA is the main reason for insufficient treatment results of LCFA-containing wastewaters (4-8). Studies of methanogenic inhibition in the rumen confirm the toxicity of these compounds. Soliva et al. (9) showed the antimethanogenic potential of saturated fatty acids of medium chain length, specifically myristate (C 14:0 ) and laurate (C 12:0 ). The adverse effect of fatty acids toward methanogens appears to be more pronounced at longer chain lengths and more unsaturated bonds (10, 11). Moreover, methanogens inhibition by fatty acids is a rapid phenomenon with long recuperation time, as shown by Koster (12): a 50% loss of methanogenic activity was observed after exposing methanogenic sludge to 7.5 mM laurate for only 7.5 min.Sensitivity of microorganisms to LCFA seems to be related to their cell wall structure, with Gram-positive bacteria and methanogens being more easily inhibited than Gram-negative bacteria (13). Inhibition of pure cultures of methanogens by fatty acids is reported in literature (11, 14). Nevertheless, methanogens are ubiquitous in anaerobic bioreactors treating LCFA-rich wastewaters, even over prolonged continuous LCFA loading (15,16). Sousa et al. (16) identified three predominant genera of methanogens in LCFA-degradi...

Untangling the Effect of Fatty Acid Addition at Species Level Revealed Different Transcriptional Responses of the Biogas Microbial Community Members

“…Till now, it was only known that the methanogens have different tolerance level toward LCFA inhibition and more specifically that hydrogenotrophic methanogens are more resilient compared to the acetoclastic ones. 41 The current research additionally proved that LCFA influence differently the hydrogenotrophic archaea even if they belong to the same genus (i.e., Methanoculleus).…”

Toxicity of long chain fatty acids towards acetate conversion by Methanosaeta concilii and Methanosarcina mazei

“…A comparison between IC 50 values obtained for oleate and palmitate towards acetoclastic methanogens in this study, and towards hydrogenotrophic methanogens (Sousa et al ., ) is presented in Table . Our results show that M. concilii and M. mazei are similarly affected by the presence of oleate as the hydrogenotroph Methanospirillum hungatei, and M. concilii seems to be even more tolerant to the presence of palmitate than M. hungatei .…”

“…In lipid‐containing wastewaters, oleate (C 18:1 ) is generally the most abundant LCFA, and palmitate (C 16:0 ) tends to accumulate in anaerobic bioreactors treating these effluents (Pereira et al ., ; Dereli et al ., ). The effect of LCFA on anaerobic sludge has been studied before (Sousa et al ., ; Palatsi et al ., ; Silva et al ., ), and a few studies report the sensitivity of pure cultures of hydrogenotrophic methanogens (Sousa et al ., ; Zhou et al ., ). Information on the sensitivity of pure cultures of acetoclastic methanogens is lacking.…”

A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars

“…The defining chemistry is inorganic: elemental inventory, liquid water, Eh, pH, redox couples, and a diversity of chemical compounds. Organic molecules are not required environmental constituents because they can be synthesized de novo through the 'primitive' autotrophic pathways such as methanogenesis and acetogenesis (67). We have measured H, O, S, C, N and P in minerals and other compounds with the APXS, ChemCam, CheMin, and SAM instruments, as well as important metals such as Fe, Mg, and Mn (19,28,52).…”