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<p>In methanogenic communities, two main pathways drive methanogenesis: acetoclastic methanogenesis, which converts acetate into CH<sub>4</sub> and CO<sub>2</sub>, and hydrogenotrophic methanogenesis, which reduces CO<sub>2</sub> with H<sub>2</sub> to CH<sub>4</sub>. Under high-pH conditions, a shift in dominance from acetoclastic to hydrogenotrophic methanogenesis is often observed. The goal of this work was to identify the pH tipping point for this metabolic shift and to elucidate the influence of alkalinity on this transition in a haloalkaliphilic methanogenic community enriched from anaerobic soda lake sediments. To this end, a haloalkaliphilic microbial community was cultivated across a pH range (8.20–10.00) at three different alkalinities (0.1, 0.6, 1.2&#xa0;eq/L). Specific qPCR probes were developed to quantify the two dominant methanogens for each catabolism: “<i>Ca. Methanocrinis natronophilus</i>” (acetoclastic) and <i>Methanocalculus alkaliphilus</i> (hydrogenotrophic). Results showed that the relative abundance of <i>Methanocalculus</i> increased with the rise of pH for all alkalinities, with alkalinity exerting a stronger influence than pH. At low alkalinity (0.1&#xa0;eq/L), <i>Methanocalculus</i> abundance doubled from 5.14 ± 1.95% to 9.15 ± 0.77% (pH 8.40–10.35). At moderate alkalinity (0.6&#xa0;eq/L), it increased from 8.33 ± 1.34% to 47.92 ± 3.76% (pH 8.41–10.00), and at the highest alkalinity (1.2&#xa0;eq/L), it increased from 6.78 ± 1.06% to 60.25 ± 2.00% (pH 8.26–9.68). 16S rRNA gene amplicon sequencing further identified “<i>Candidatus</i> Contubernalis” as a putative syntrophic acetate-oxidizing bacterium likely partnering with <i>Methanocalculus</i> in indirect hydrogenotrophic methanogenesis. This work highlights that haloalkaliphilic hydrogenotrophic methanogens offer a promising strategy to integrate CO<sub>2</sub> capture in alkaline solutions with biomethanation.</p>

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Acetoclastic versus hydrogenotrophic methanogenesis: defining how pH and alkalinity shape acetate metabolism in a haloalkaliphilic methanogenic community for biomethane production

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年2月16日

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  • Beatriz C. Diniz,
  • Ben Abbas,
  • Dimitry Y. Sorokin,
  • Mark C. M. van Loosdrecht,
  • Philipp Zantout-Wilfert

摘要

In methanogenic communities, two main pathways drive methanogenesis: acetoclastic methanogenesis, which converts acetate into CH4 and CO2, and hydrogenotrophic methanogenesis, which reduces CO2 with H2 to CH4. Under high-pH conditions, a shift in dominance from acetoclastic to hydrogenotrophic methanogenesis is often observed. The goal of this work was to identify the pH tipping point for this metabolic shift and to elucidate the influence of alkalinity on this transition in a haloalkaliphilic methanogenic community enriched from anaerobic soda lake sediments. To this end, a haloalkaliphilic microbial community was cultivated across a pH range (8.20–10.00) at three different alkalinities (0.1, 0.6, 1.2 eq/L). Specific qPCR probes were developed to quantify the two dominant methanogens for each catabolism: “Ca. Methanocrinis natronophilus” (acetoclastic) and Methanocalculus alkaliphilus (hydrogenotrophic). Results showed that the relative abundance of Methanocalculus increased with the rise of pH for all alkalinities, with alkalinity exerting a stronger influence than pH. At low alkalinity (0.1 eq/L), Methanocalculus abundance doubled from 5.14 ± 1.95% to 9.15 ± 0.77% (pH 8.40–10.35). At moderate alkalinity (0.6 eq/L), it increased from 8.33 ± 1.34% to 47.92 ± 3.76% (pH 8.41–10.00), and at the highest alkalinity (1.2 eq/L), it increased from 6.78 ± 1.06% to 60.25 ± 2.00% (pH 8.26–9.68). 16S rRNA gene amplicon sequencing further identified “Candidatus Contubernalis” as a putative syntrophic acetate-oxidizing bacterium likely partnering with Methanocalculus in indirect hydrogenotrophic methanogenesis. This work highlights that haloalkaliphilic hydrogenotrophic methanogens offer a promising strategy to integrate CO2 capture in alkaline solutions with biomethanation.