Bioconversion of coal: New insights from a core flooding study

A pressurized core flooding experiment was performed to better understand in situ coal bioconversion processes. The core flooding experiment was conducted using a biaxial core holder packed with subbituminous coal particles (250-150 μm grain size) obtained from the Highvale mine in Alberta, Canada. The coal pack was inoculated with a methanogenic microbial culture enriched from coal and was continuously flooded with mineral salt medium and an organic carbon/nitrogen nutrient supplement (tryptone). The changes in the physical properties of the coal pack during the core flooding suggested coal bioconversion to methane under the experimental conditions. Colonization and bioconversion of coal by microbes was evident from the change in core permeability and presence of metabolites and gas (CH4 and CO 2) in the effluent. A total of 1.52 μmol of CH4 was produced per gram of coal during the 90 days experiment at 22 °C. Signature metabolites consistent with anaerobic biodegradation of hydrocarbons, e.g., carboxylic acids, were identified in effluent samples throughout incubation. The transient nature of metabolites in effluent samples supports fermentation of coal constituents and nutrient supplement to simple molecules such as acetic acid, which served as a substrate for methanogenesis during the bioconversion process. Accumulation of carboxylic acids such as succinic acid in the effluent also demonstrates that the coal bioconversion process may be used for extraction of other value-added products apart from CH4 generation. Importantly, results presented here suggest that coal bioconversion by biostimulation under reservoir conditions is a scalable technology with potential for energy generation and for overall reduction of greenhouse gas emissions. This journal i

Genomic analysis of the mesophilic Thermotogae genus Mesotoga reveals phylogeographic structure and genomic determinants of its distinct metabolism

The genus Mesotoga , the only described mesophilic Thermotogae lineage, is common in mesothermic anaerobic hydrocarbon‐rich environments. Besides mesophily, Mesotoga displays lineage‐specific phenotypes, such as no or little H2 production and dependence on sulfur‐compound reduction, which may influence its ecological role. We used comparative genomics of 18 Mesotoga strains (pairwise 16S rRNA identity >99%) and a transcriptome of M. prima to investigate how life at moderate temperatures affects phylogeography and to interrogate the genomic features of its lineage‐specific metabolism. We propose that Mesotoga accomplish H2 oxidation and thiosulfate reduction using a sulfide dehydrogenase and a hydrogenase‐complex and that a pyruvate:ferredoxin oxidoreductase acquired from Clostridia is responsible for oxidizing acetate. Phylogenetic analysis revealed three distinct Mesotoga lineages (89.6%–99.9% average nucleotide identity [ANI] within lineages, 79.3%–87.6% ANI between lineages) having different geographic distribution patterns and high levels of intra‐lineage recombination but little geneflow between lineages. Including data from metagenomes, phylogeographic patterns suggest that geographical separation historically has been more important for Mesotoga than hyperthermophilic Thermotoga and we hypothesize that distribution of Mesotoga is constrained by their anaerobic lifestyle. Our data also suggest that recent anthropogenic activities and environments (e.g., wastewater treatment, oil exploration) have expanded Mesotoga habitats and dispersal capabilities