Influence of ion exchange membrane types on microbial electrosynthesis performance and biomethane production

Microbial electrosynthesis (MES) utilizes electrical current to convert CO2 into various products via electroactive microbial activity at the cathode. Methane production in MES relies on methanogens within the cathode biofilm and is influenced by various factors including the type of ion exchange membrane, which plays a critical role but remains underexplored, particularly regarding ion transport mechanisms. This study examined methane production in MES reactors equipped with cation exchange membranes (CEM-MES) and anion exchange membranes (AEM-MES) at cathodic potentials of -1.0 to -1.2 V (vs. Ag/AgCl). AEM-MES produced 10.1 times more methane than CEM-MES. Despite elevated catholyte pH and greater pH imbalances in AEM-MES, methane production was primarily governed by H2 production rate rather than pH imbalance. The microbial community of cathode biofilm was significantly influenced by membrane type, with Methanobacterium prevailing in AEM-MES, correlating with reactor performance. AEM-MES demonstrated enhanced methane production, particularly at cathodic potentials that minimized hydrogen evolution.

Proposal of Neomoorella gen. nov. as a replacement name for the illegitimate prokaryotic genus name Moorella Collins et al. 1994

Following Rule 51b(4) of the International Code of Nomenclature of Prokaryotes (2022 Revision) (ICNP), the prokaryotic generic name Moorella Collins et al. 1994 is illegitimate, as it is a later homonym of the fungal genus name Moorella P. Rag. Rao & D. Rao 1964 (Ascomycota: Pezizomycotina). Accordingly, as required by Rule 54 of the ICNP, we propose the replacement name Neomoorella and the replacement type species name Neomoorella thermoacetica. We also propose replacement names for the six other species with validly published and not rejected names belonging to the genus Moorella, for one species with effectively but not validly published name and for the family name Moorellaceae and the order name Moorellales.

Methanol transfer supports metabolic syntrophy between bacteria and archaea

In subsurface methanogenic ecosystems, the ubiquity of methylated-compound-using archaea-methylotrophic methanogens1-4-implies that methylated compounds have an important role in the ecology and carbon cycling of such habitats. However, the origin of these chemicals remains unclear5,6 as there are no known energy metabolisms that generate methylated compounds de novo as a major product. Here we identified an energy metabolism in the subsurface-derived thermophilic anaerobe Zhaonella formicivorans7 that catalyses the conversion of formate to methanol, thereby producing methanol without requiring methylated compounds as an input. Cultivation experiments showed that formate-driven methanologenesis is inhibited by the accumulation of methanol. However, this limitation can be overcome through methanol consumption by a methylotrophic partner methanogen, Methermicoccus shengliensis. This symbiosis represents a fourth mode of mutualistic cross-feeding driven by thermodynamic necessity (syntrophy), previously thought to rely on transfer of hydrogen, formate or electrons8-10. The unusual metabolism and syntrophy provide insights into the enigmatic presence of methylated compounds in subsurface methanogenic ecosystems and demonstrate how organisms survive at the thermodynamic limit through metabolic symbiosis.

Isolation and genomic analysis of "Metallumcola ferriviriculae" MK1, a Gram-positive, Fe(III)-reducing bacterium from the Soudan Underground Mine, an iron-rich Martian analog site

The Soudan Underground Mine State Park, found in the Vermilion Iron Range in northern Minnesota, provides access to a ~ 2.7 billion-year-old banded iron formation. Exploratory boreholes drilled between 1958 and 1962 on the 27th level (713 m underground) of the mine intersect calcium and iron-rich brines that have recently been subject to metagenomic analysis and microbial enrichments. Using concentrated brine samples pumped from a borehole depth of up to 55 m, a novel Gram-positive bacterium was enriched under anaerobic, acetate-oxidizing, and Fe(III) citrate-reducing conditions. The isolated bacterium, designated strain MK1, is non-motile, rod-shaped, spore-forming, anaerobic, and mesophilic, with a growth range between 24°C and 30°C. The complete circular MK1 genome was found to be 3,720,236 bp and encodes 25 putative multiheme cytochromes, including homologs to inner membrane cytochromes in the Gram-negative bacterium Geobacter sulfurreducens and cytoplasmic membrane and periplasmic cytochromes in the Gram-positive bacterium Thermincola potens. However, MK1 does not encode homologs of the peptidoglycan (CwcA) and cell surface-associated (OcwA) multiheme cytochromes proposed to be required by T. potens to perform extracellular electron transfer. The 16S rRNA gene sequence of MK1 indicates that its closest related isolate is Desulfitibacter alkalitolerans strain sk.kt5 (91% sequence identity), which places MK1 in a novel genus within the Desulfitibacteraceae family and Moorellales order. Within the Moorellales order, only Calderihabitans maritimus strain KKC1 has been reported to reduce Fe(III), and only D. alkalitolerans can also grow in temperatures below 40°C. Thus, MK1 represents a novel species within a novel genus, for which we propose the name "Metallumcola ferriviriculae" strain MK1, and provides a unique opportunity to study a cytochrome-rich, mesophilic, Gram-positive, spore-forming Fe(III)-reducing bacterium.IMPORTANCEThe Soudan Underground Mine State Park gives access to understudied regions of the deep terrestrial subsurface that potentially predate the Great Oxidation Event. Studying organisms that have been relatively unperturbed by surface conditions for as long as 2.7 billion years may give us a window into ancient life before oxygen dominated the planet. Additionally, studying microbes from anoxic and iron-rich environments can help us better understand the requirements of life in analogous environments, such as on Mars. The isolation and characterization of "Metallumcola ferriviriculae" strain MK1 give us insights into a novel genus and species that is distinct both from its closest related isolates and from iron reducers characterized to date. "M. ferriviriculae" strain MK1 may also act as a model organism to study how the processes of sporulation and germination are affected by insoluble extracellular acceptors, as well as the impact of spores in the deep terrestrial biosphere.

Isolation and characterization of novel acetogenic Moorella strains for employment as potential thermophilic biocatalysts

Thermophilic acetogenic bacteria have attracted attention as promising candidates for biotechnological applications such as syngas fermentation, microbial electrosynthesis, and methanol conversion. Here, we aimed to isolate and characterize novel thermophilic acetogens from diverse environments. Enrichment of heterotrophic and autotrophic acetogens was monitored by 16S rRNA gene-based bacterial community analysis. Seven novel Moorella strains were isolated and characterized by genomic and physiological analyses. Two Moorella humiferrea isolates showed considerable differences during autotrophic growth. The M. humiferrea LNE isolate (DSM 117358) fermented carbon monoxide (CO) to acetate, while the M. humiferrea OCP isolate (DSM 117359) transformed CO to hydrogen and carbon dioxide (H2 + CO2), employing the water-gas shift reaction. Another carboxydotrophic hydrogenogenic Moorella strain was isolated from the covering soil of an active charcoal burning pile and proposed as the type strain (ACPsT) of the novel species Moorella carbonis (DSM 116161T and CCOS 2103T). The remaining four novel strains were affiliated with Moorella thermoacetica and showed, together with the type strain DSM 2955T, the production of small amounts of ethanol from H2 + CO2 in addition to acetate. The physiological analyses of the novel Moorella strains revealed isolate-specific differences that considerably increase the knowledge base on thermophilic acetogens for future applications.

Whither the genus Caldicellulosiruptor and the order Thermoanaerobacterales: phylogeny, taxonomy, ecology, and phenotype

The order Thermoanaerobacterales currently consists of fermentative anaerobic bacteria, including the genus Caldicellulosiruptor. Caldicellulosiruptor are represented by thirteen species; all, but one, have closed genome sequences. Interest in these extreme thermophiles has been motivated not only by their high optimal growth temperatures (≥70°C), but also by their ability to hydrolyze polysaccharides including, for some species, both xylan and microcrystalline cellulose. Caldicellulosiruptor species have been isolated from geographically diverse thermal terrestrial environments located in New Zealand, China, Russia, Iceland and North America. Evidence of their presence in other terrestrial locations is apparent from metagenomic signatures, including volcanic ash in permafrost. Here, phylogeny and taxonomy of the genus Caldicellulosiruptor was re-examined in light of new genome sequences. Based on genome analysis of 15 strains, a new order, Caldicellulosiruptorales, is proposed containing the family Caldicellulosiruptoraceae, consisting of two genera, Caldicellulosiruptor and Anaerocellum. Furthermore, the order Thermoanaerobacterales also was re-assessed, using 91 genome-sequenced strains, and should now include the family Thermoanaerobacteraceae containing the genera Thermoanaerobacter, Thermoanaerobacterium, Caldanaerobacter, the family Caldanaerobiaceae containing the genus Caldanaerobius, and the family Calorimonaceae containing the genus Calorimonas. A main outcome of ANI/AAI analysis indicates the need to reclassify several previously designated species in the Thermoanaerobacterales and Caldicellulosiruptorales by condensing them into strains of single species. Comparative genomics of carbohydrate-active enzyme inventories suggested differentiating phenotypic features, even among strains of the same species, reflecting available nutrients and ecological roles in their native biotopes.

Improved understanding on biochar effect in electron supplied anaerobic soil as evidenced by dechlorination and methanogenesis processes

Research interest in biochar as an environmental remediation material has rapidly increased over the past few years. However, the effect of biochar on typical environmental processes in anaerobic soil environment has been insufficiently discussed. By regulating the electron donors with sodium acetate or pyruvate, the effects and underpinning chemical-microbiological coupling mechanisms of biochar under anaerobic conditions were disclosed. Unlike the electron limited condition, the addition of electron donors alleviated the competition for electrons among various reduction processes in the soil. The effect of biochar in regulating the electron transfer processes was lessened. But more than doubled methane emissions were resulted by the exogenous substances, especially with the synergic effect of biochar. Biochar addition increased soil environmental heterogeneity. It might indirectly affect the reductive transformation of γ-HCH via increasing the bioavailability of pollutants through adsorption and promoting the metabolism of some rare microorganisms. Anaerolineaceae, Peptococcaceae and Methanosarcina had coherent phylogenetic patterns and were likely to be the enablers for the reductive dechlorination process in flooded soil. ENVIRONMENTAL IMPLICATION: Previous studies have widely reported the performance characteristics of biochar, but its effects under anaerobic environments are not systematically understood. By regulating the electron donors, the competition for electrons among various reduction processes in the soil might be alleviated, resulting in a lessened effect of biochar in regulating the electron transfer processes. The findings presented in this study highlight the role of biochar to the dynamic changes of reduction processes under anaerobic environments. The relevant soil conditions such as the electron donors and the functional microbial groups should be adequately considered for maximizing the all-around beneficial efficiency of biochar amendments.

Combined partial denitrification-anammox with urea hydrolysis (U-PD-Anammox) process: A novel economical low-carbon method for nitrate-containing wastewater treatment

For the sake of exploring a new economical and low-carbon alternative for real nitrate-containing wastewater treatment, a new combined partial denitrification-anammox with urea hydrolysis (U-PD-Anammox) process was developed. The nitrogen removal performance of this process was investigated through long-term operation in a sequencing batch reactor (SBR) and two submerged anaerobic biological filters (SABF). Results showed that the average NO₃^--N to NO₂^-N transformation ratio improved to 82.6% with organic carbon source to NO₃^-N ratio of 1.8, and urea hydrolysis provided sufficient NH₄⁺-N and inorganic carbon to anammox process for nitrogen removal. The influent NH₄⁺-N/NO₂^--N ratio for subsequent anammox reactor could be adjacent to the optimal ratio of 1.32 during the whole operation. The combined process showed efficient nitrogen removal performance with 85% NO₃^--N removal, 93.8% total nitrogen removal and total nitrogen loading rate as 1.1 ± 0.5 kg N/(m³·d). High-throughput sequencing analysis results revealed that Genera Thauera, Hyphomicrobium and Candidatus Brocadia were the dominant species responsible for partial denitrification, urea hydrolysis and anammox, respectively. The proposed process was more economically and environmental-friendly than the traditional denitrification process with 51.7% operational cost reduction, 99.7% N₂O and 60% CO₂ emission decrement, facilitating the sustainable development of the nitrate-containing wastewater treatment industry in the future.

Koleobacter methoxysyntrophicus gen. nov., sp. nov., a novel anaerobic bacterium isolated from deep subsurface oil field and proposal of Koleobacteraceae fam. nov. and Koleobacterales ord. nov. within the class Clostridia of the phylum Firmicutes

An anaerobic thermophilic, rod-shaped bacterium possessing a unique non-lipid sheathed-like structure enveloping a single-membraned cell, designated strain NRmbB1^T was isolated from at the deep subsurface oil field located in Yamagata Prefecture, Japan. Growth occurred with 40-60°C (optimum, 55°C), 0-2% (2%), NaCl and pH 6.0-8.5 (8.0). Fermentative growth with various sugars was observed. Glucose-grown cells generated acetate, hydrogen, pyruvate and lactate as the main end products. Syntrophic growth occurred with glucose, pyruvate and 3,4,5-trimethoxybenzoate in the presence of an H₂-scavenging partner, and growth on 3,4,5-trimethoxybenzoate was only observed under syntrophic condition. The predominant cellular fatty acids were C_16:0, iso-C_16:0, anteiso-C_15:0, and iso-C_14:0. Respiratory quinone was not detected. The genomic G+C content was 40.8mol%. Based on 16S rRNA gene phylogeny, strain NRmbB1^T belongs to a distinct order-level clade in the class Clostridia of the phylum Firmicutes, sharing low similarity with other isolated organisms (i.e., 87.5% for top hit Moorella thermoacetica DSM 2955^T). In total, chemotaxonomic, phylogenetic and genomic characterization revealed that strain NRmbB1^T (=KCTC 25035^T, =JCM 39120^T) represents a novel species of a new genus. In addition, we also propose the associated family and order as Koleobacteraceae fam. nov and Koleobacterales ord. nov., respectively.