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

Abstract

SummaryLong‐chain fatty acids (LCFA) can inhibit methane production by methanogenic archaea. The effect of oleate and palmitate on pure cultures of Methanosaeta concilii and Methanosarcina mazei was assessed by comparing methane production rates from acetate before and after LCFA addition. For both methanogens, a sharp decrease in methane production (> 50%) was observed at 0.5 mmol L−1 oleate, and no methane was formed at concentrations higher than 2 mmol L−1 oleate. Palmitate was less inhibitory than oleate, and M. concilii was more tolerant to palmitate than M. mazei, with 2 mmol L−1 palmitate causing 11% and 64% methanogenic inhibition respectively. This study indicates that M. concilii and M. mazei tolerate LCFA concentrations similar to those previously described for hydrogenotrophic methanogens. In particular, the robustness of M. concilii might contribute to the observed prevalence of Methanosaeta species in anaerobic bioreactors used to treat LCFA‐rich wastewater.

Long-chain fatty acid feeding frequency in anaerobic codigestion impacts syntrophic community structure and biokinetics

“…In this study, Methanosaeta was the dominant aceticlastic group in both codigesters, despite acetate accumulation to over 3,000 mg/L in the CF codigester and periodic acetate accumulation to 500-1,000 mg/L in the PF2 codigester. A higher tolerance to LCFA was reported for pure cultures of Methanosaeta concilii in comparison to Methanosarcina mazei (Silva et al, 2016), which could explain the presence of Methanosaeta rather than Methanosarcina in our study codigesters.…”

“…The bacterial species known to β-oxidize LCFA in syntrophy with a hydrogen-or formate-consuming partner have so far been identified within only two families, Syntrophomonadaceae and Syntrophaceae (Sousa et al, 2009). The slower biodegradation of LCFA relative to lipid hydrolysis in anaerobic digesters can lead to LCFA accumulation and process instability, as LCFA are known inhibitors of hydrogenotrophic and aceticlastic methanogenic activity at high concentrations (Hanaki et al, 1981;Hwu and Lettinga, 1997;Silva et al, 2016;Sousa et al, 2013). LCFA accumulation can also limit the kinetics of syntrophic βoxidizing bacteria (Hanaki et al, 1981).…”

“…Such models have also represented LCFA-degrading bacteria as a single homogenous population, whereas it was previously shown that various LCFA-degrading taxa can coexist in anaerobic digester sludge (Sousa et al, 2007;Treu et al, 2016;Ziels et al, 2015) with potentially different functional roles (Kougias et al, 2016). Different methanogenic archaea species can also have varying degrees of tolerance to LCFA exposure (Silva et al, 2016;Sousa et al, 2013), suggesting that the digester methanogen community structure could be affected by FOG addition. A recent finding that effluent LCFA concentrations were inversely correlated to LCFA-degrading bacteria 16S rRNA gene concentrations during FOG codigestion (Ziels et al, 2016) implicated that the maximum LCFA bioconversion rate of syntrophic bacteria and methanogenic archaea could establish the allowable FOG loading rate possible before LCFA accumulation.…”

Ecophysiology of Acetoclastic Methanogens

“…However, there are examples where Methanothrix seems to be more resistant. Methanothrix is more resistant to longchain fatty acids (Silva et al 2016) and humic substances (Azman et al 2017) than Methanosarcina. The higher tolerance in these cases was thought to be related to the different cell wall structure.…”

Ecophysiology of Acetoclastic Methanogens

“…However, there are examples where Methanothrix seems to be more resistant. Methanothrix is more resistant to longchain fatty acids (Silva et al 2016) and humic substances (Azman et al 2017) than Methanosarcina. The higher tolerance in these cases was thought to be related to the different cell wall structure.…”