Expression of divergent methyl/alkyl coenzyme M reductases from uncultured archaea

The crystal structure of methanogen McrD, a methyl-coenzyme M reductase-associated protein

Methyl-coenzyme M reductase (MCR) is a multi-subunit (α2β2γ2) enzyme responsible for methane formation via its unique F430 cofactor. The genes responsible for producing MCR (mcrA, mcrB and mcrG) are typically colocated with two other highly conserved genes mcrC and mcrD. We present here the high-resolution crystal structure for McrD from a human gut methanogen Methanomassiliicoccus luminyensis strain B10. The structure reveals that McrD comprises a ferredoxin-like domain assembled into an α + β barrel-like dimer with conformational flexibility exhibited by a functional loop. The description of the M. luminyensis McrD crystal structure contributes to our understanding of this key conserved methanogen protein typically responsible for promoting MCR activity and the production of methane, a greenhouse gas.

Biocatalysis of CO2 and CH4: Key enzymes and challenges

Mitigating greenhouse gas emissions is a critical challenge for promoting global sustainability. The utilization of CO2 and CH4 as substrates for the production of valuable products offers a promising avenue for establishing an eco-friendly economy. Biocatalysis, a sustainable process utilizing enzymes to facilitate biochemical reactions, plays a significant role in upcycling greenhouse gases. This review provides a comprehensive overview of the enzymes and associated reactions involved in the biocatalytic conversion of CO2 and CH4. Furthermore, the challenges facing the field are discussed, paving the way for future research directions focused on developing robust enzymes and systems for the efficient fixation of CO2 and CH4.

Genomic language model predicts protein co-regulation and function

Deciphering the relationship between a gene and its genomic context is fundamental to understanding and engineering biological systems. Machine learning has shown promise in learning latent relationships underlying the sequence-structure-function paradigm from massive protein sequence datasets. However, to date, limited attempts have been made in extending this continuum to include higher order genomic context information. Evolutionary processes dictate the specificity of genomic contexts in which a gene is found across phylogenetic distances, and these emergent genomic patterns can be leveraged to uncover functional relationships between gene products. Here, we train a genomic language model (gLM) on millions of metagenomic scaffolds to learn the latent functional and regulatory relationships between genes. gLM learns contextualized protein embeddings that capture the genomic context as well as the protein sequence itself, and encode biologically meaningful and functionally relevant information (e.g. enzymatic function, taxonomy). Our analysis of the attention patterns demonstrates that gLM is learning co-regulated functional modules (i.e. operons). Our findings illustrate that gLM's unsupervised deep learning of the metagenomic corpus is an effective and promising approach to encode functional semantics and regulatory syntax of genes in their genomic contexts and uncover complex relationships between genes in a genomic region.

Metagenomic profiles of archaea and bacteria within thermal and geochemical gradients of the Guaymas Basin deep subsurface

Previous studies of microbial communities in subseafloor sediments reported that microbial abundance and diversity decrease with sediment depth and age, and microbes dominating at depth tend to be a subset of the local seafloor community. However, the existence of geographically widespread, subsurface-adapted specialists is also possible. Here, we use metagenomic and metatranscriptomic analyses of the hydrothermally heated, sediment layers of Guaymas Basin (Gulf of California, Mexico) to examine the distribution and activity patterns of bacteria and archaea along thermal, geochemical and cell count gradients. We find that the composition and distribution of metagenome-assembled genomes (MAGs), dominated by numerous lineages of Chloroflexota and Thermoproteota, correlate with biogeochemical parameters as long as temperatures remain moderate, but downcore increasing temperatures beyond ca. 45 ºC override other factors. Consistently, MAG size and diversity decrease with increasing temperature, indicating a downcore winnowing of the subsurface biosphere. By contrast, specific archaeal MAGs within the Thermoproteota and Hadarchaeota increase in relative abundance and in recruitment of transcriptome reads towards deeper, hotter sediments, marking the transition towards a specialized deep, hot biosphere.

Respiration-driven methanotrophic growth of diverse marine methanogens

Anaerobic marine environments are the third largest producer of the greenhouse gas methane. The release to the atmosphere is prevented by anaerobic 'methanotrophic archaea (ANME) dependent on a symbiotic association with sulfate-reducing bacteria or direct reduction of metal oxides. Metagenomic analyses of ANME are consistent with a reverse methanogenesis pathway, although no wild-type isolates have been available for validation and biochemical investigation. Herein is reported the characterization of methanotrophic growth for the diverse marine methanogens Methanosarcina acetivorans C2A and Methanococcoides orientis sp. nov. Growth was dependent on reduction of either ferrihydrite or humic acids revealing a respiratory mode of energy conservation. Acetate and/or formate were end products. Reversal of the well-characterized methanogenic pathways is remarkably like the consensus pathways for uncultured ANME based on extensive metagenomic analyses.

From methane to value-added bioproducts: microbial metabolism, enzymes, and metabolic engineering

Methane is abundant in nature, and excessive emissions will cause the greenhouse effect. Methane is also an ideal carbon and energy feedstock for biosynthesis. In the review, the microorganisms, metabolism, and enzymes for methane utilization, and the advances of conversion to value-added bioproducts were summarized. First, the physiological characteristics, classification, and methane oxidation process of methanotrophs were introduced. The metabolic pathways for methane utilization and key intermediate metabolites of native and synthetic methanotrophs were summarized. Second, the enzymatic properties, crystal structures, and catalytic mechanisms of methane-oxidizing and metabolizing enzymes in methanotrophs were described. Third, challenges and prospects in metabolic pathways and enzymatic catalysis for methane utilization and conversion to value-added bioproducts were discussed. Finally, metabolic engineering of microorganisms for methane biooxidation and bioproducts synthesis based on different pathways were summarized. Understanding the metabolism and challenges of microbial methane utilization will provide insights into possible strategies for efficient methane-based synthesis.

A high-value biohythane production: Feedstocks, reactor configurations, pathways, challenges, technoeconomics and applications

In recent years, the demand for high-quality biofuels from renewable sources has become an aspirational goal to offer a clean environment by alternating the depleting fossil fuels to meet future energy needs. In this aspect, biohythane production from wastes has received extensive research interest since it contains superior fuel characteristics than the promising conventional biofuel i.e. biogas. The main aim is to promote research and potentials of biohythane production by a systematic review of scientific literature on the biohythane production pathways, substrate/microbial consortium suitability, reactor design, and influential process/operational factors. Reactor configuration also decides the product yield in addition to other key factors like waste composition, temperature, pH, retention time and loading rates. Hence, a detailed emphasis on different reactor configurations with respect to the type of feedstock has also been given. The technical challenges are highlighted towards process optimization and system scale up. Meanwhile, solutions to improve product yield, technoeconomics, applications and key policy and governance factors to build a hydrogen based society have also been discussed.

The methanogen core and pangenome: conservation and variability across biology's growth temperature extremes

Temperature is a key variable in biological processes. However, a complete understanding of biological temperature adaptation is lacking, in part because of the unique constraints among different evolutionary lineages and physiological groups. Here we compared the genomes of cultivated psychrotolerant and thermotolerant methanogens, which are physiologically related and span growth temperatures from -2.5°C to 122°C. Despite being phylogenetically distributed amongst three phyla in the archaea, the genomic core of cultivated methanogens comprises about one-third of a given genome, while the genome fraction shared by any two organisms decreases with increasing phylogenetic distance between them. Increased methanogenic growth temperature is associated with reduced genome size, and thermotolerant organisms-which are distributed across the archaeal tree-have larger core genome fractions, suggesting that genome size is governed by temperature rather than phylogeny. Thermotolerant methanogens are enriched in metal and other transporters, and psychrotolerant methanogens are enriched in proteins related to structure and motility. Observed amino acid compositional differences between temperature groups include proteome charge, polarity and unfolding entropy. Our results suggest that in the methanogens, shared physiology maintains a large, conserved genomic core even across large phylogenetic distances and biology's temperature extremes.