New microbial electrosynthesis system for methane production from carbon dioxide coupled with oxidation of sulfide to sulfate

Microbial electrosynthesis system (MES) is a promising method that can use carbon dioxide,which is a greenhouse gas,to produce methane which acts as an energy source,without using organic substances.However,this bioelectrical reduction reaction can proceed at a certain high applied voltage when coupled with water oxidation in the anode coated with metallic catalyst.When coupled with the oxidation of HS–to SO_(4)^(2-),methane production is thermodynamically more feasible,thus implying its production at a considerably lower applied voltage.In this study,we demonstrated the possibility of electrotrophic methane production coupled with HS–oxidation in a cost-effective bioanode chamber in the MES without organic substrates at a low applied voltage of 0.2 V.In addition,microbial community analyses of biomass enriched in the bioanode and biocathode were used to reveal the most probable pathway for methane production from HS–oxidation.In the bioanode,electroautotrophic SO_(4)^(2-)production accompanied with electron donation to the electrode is performed mainly by the following two steps:first,incomplete sulfide oxidation to sulfur cycle intermediates (SCI) is performed;then the produced SCI are disproportionated to HS^(–)and SO_(4)^(2-).In the biocathode,methane is produced mainly via H_(2)and acetate by electronaccepting syntrophic bacteria,homoacetogens,and acetoclastic archaea.Here,a new ecofriendly MES with biological H_(2)S removal is established.

Biological methane production coupled with sulfur oxidation in a microbial electrosynthesis system without organic substrates

Methane is produced in a microbial electrosynthesis system(MES) without organic substrates. However, a relatively high applied voltage is required for the bioelectrical reactions.In this study, we demonstrated that electrotrophic methane production at the biocathode was achieved even at a very low voltage of 0.1 V in an MES, in which abiotic HS-oxidized to SO_(4)^(2-) at the anodic carbon-cloth surface coated with platinum powder. In addition, microbial community analysis revealed the most probable pathway for methane production from electrons. First, electrotrophic H_(2) was produced by syntrophic bacteria, such as Syntrophorhabdus, Syntrophobacter, Syntrophus, Leptolinea, and Aminicenantales, with the direct acceptance of electrons at the biocathode. Subsequently, most of the produced H_(2) was converted to acetate by homoacetogens, such as Clostridium and Spirochaeta 2. In conclusion,the majority of the methane was indirectly produced by a large population of acetoclastic methanogens, namely Methanosaeta, via acetate. Further, hydrogenotrophic methanogens,including Methanobacterium and Methanolinea, produced methane via H_(2).

Co anchored on porphyrinic triazine-based frameworks with excellent biocompatibility for conversion of CO_(2)in H_(2)-mediated microbial electrosynthesis

Microbial electrosynthesis is a promising alternative to directly convert CO_(2)into long-chain compounds by coupling inorganic electrocatalysis with biosynthetic systems.However,problems arose that the conventional electrocatalysts for hydrogen evolution may produce extensive by-products of reactive oxygen species and cause severe metal leaching,both of which induce strong toxicity toward microorganisms.Moreover,poor stability of electrocatalysts cannot be qualified for long-term operation.These problems may result in poor biocompatibility between electrocatalysts and microorganisms.To solve the bottleneck problem,Co anchored on porphyrinic triazine-based frameworks was synthesized as the electrocatalyst for hydrogen evolution and further coupled with Cupriavidus necator H16.It showed high selectivity for a four-electron pathway of oxygen reduction reaction and low production of reactive oxygen species,owing to the synergistic effect of Co–Nx modulating the charge distribution and adsorption energy of intermediates.Additionally,low metal leaching and excellent stability were observed,which may be attributed to low content of Co and the stabilizing effect of metalloporphyrins.Hence,the electrocatalyst exhibited excellent biocompatibility.Finally,the microbial electrosynthesis system equipped with the electrocatalyst successfully converted CO_(2)to poly-β-hydroxybutyrate.This work drew up a novel strategy for enhancing the biocompatibility of electrocatalysts in microbial electrosynthesis system.

Abiotic-Biological Hybrid Systems for CO2 Conversion to Value-Added Chemicals and Fuels

Abiotic-biological hybrid systems that combine the advantages of abiotic catalysis and biotransformation for the conversion of carbon dioxide(CO2)to value-added chemicals and fuels have emerged as an appealing way to address the global energy and environmental crisis caused by increased CO2 emission.We illustrate the recent progress in this field.Here,we first review the natural CO2 fixation pathways for an in-depth understanding of the biological CO2 transformation strategy and why a sustainable feed of reducing power is important.Second,we review the recent progress in the construction of abiotic-biological hybrid systems for CO2 transformation from two aspects:(i)microbial electrosynthesis systems that utilize electricity to support whole-cell biological CO2 conversion to products of interest and(ii)photosynthetic semiconductor biohybrid systems that integrate semiconductor nanomaterials with CO2-fixing microorganisms to harness solar energy for biological CO2 transformation.Lastly,we discuss potential approaches for further improvement of abiotic-biological hybrid systems.

Microbial electro-fermentation for synthesis of chemicals and biofuels driven by bi-directional extracellular electron transfer

Electroactive bacteria could perform bi-directional extracellular electron transfer(EET)to exchange electrons and energy with extracellular environments,thus playing a central role in microbial electro-fermentation(EF)process.Unbalanced fermentation and microbial electrosynthesis are the main pathways to produce value-added chemicals and biofuels.However,the low efficiency of the bi-directional EET is a dominating bottleneck in these processes.In this review,we firstly demonstrate the main bi-directional EET mechanisms during EF,including the direct EET and the shuttle-mediated EET.Then,we review representative milestones and progresses in unbalanced fermentation via anode outward EET and microbial electrosynthesis via inward EET based on these two EET mechanisms in detail.Furthermore,we summarize the main synthetic biology strategies in improving the bi-directional EET and target products synthesis,thus to enhance the efficiencies in unbalanced fermentation and microbial electrosynthesis.Lastly,a perspective on the applications of microbial electro-fermentation is provided.