Direct interspecies electron transfer enables anaerobic oxidation of sulfide to elemental sulfur coupled with CO2-reducing methanogenesis

Heejung Jung; Hyeonjung Yu; Changsoo Lee

doi:10.1016/j.isci.2023.107504

Direct interspecies electron transfer enables anaerobic oxidation of sulfide to elemental sulfur coupled with CO₂-reducing methanogenesis

iScience. 2023 Aug 1;26(9):107504. doi: 10.1016/j.isci.2023.107504. eCollection 2023 Sep 15.

Authors

Heejung Jung¹, Hyeonjung Yu¹, Changsoo Lee^{1

2}

Affiliations

¹ Department of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Eonyang-eup, Ulju-gun, Ulsan 44919, Republic of Korea.
² Graduate School of Carbon Neutrality, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Eonyang-eup, Ulju-gun, Ulsan 44919, Republic of Korea.

Abstract

Electric syntrophy between fatty acid oxidizers and methanogens through direct interspecies electron transfer (DIET) is essential for balancing acidogenesis and methanogenesis in anaerobic digestion. Promoting DIET using electrically conductive additives proved effective in enhancing methanogenesis; however, its possibility to affect other microbial redox reactions in methanogenic systems has been little studied. This study provides the first confirmation of the electro-syntrophic coupling of sulfide oxidation to S⁰ with CO₂-reducing methanogenesis in sulfur-rich methanogenic cultures supplemented with conductive magnetite (100-700-nm particle size). The H₂S content in biogas, initially exceeding 5000 ppmv, decreased to below 1 ppmv along with an accumulation of extracellular S⁰ (60-70 mg/L; initially <1 mg/L) at a magnetite dose of 20 mM Fe, while there were no significant changes in methane yield. A comprehensive polyphasic approach demonstrated that the S⁰ formation occurs through electro-syntrophic oxidation of sulfide coupled with CO₂-reducing methanogenesis, involving Methanothrix as the dominant methanogen.

Keywords: Biocatalysis; Nanotechnology.