Dong, Xiuzhu

Summary Anaerobic oxidation of methane (AOM) is a microbial process degrading ample methane in anoxic environments, and Ca. Methanoperedens mediated nitrate‐ or metal‐reduction linked AOM is believed important in freshwater systems. This work, via 16S rRNA gene diversity survey and 16S rRNA quantification, found abundant Ca. Methanoperedens along with iron in the cold Zoige wetland at Tibetan Plateau. The wetland soil microcosm performed Fe(III) reduction, rather than nitrate‐ nor sulphate‐reduction, coupled methane oxidation (3.87 μmol d −1 ) with 32.33 μmol Fe(II) accumulation per day at 18°C, but not at 30°C. A metagenome‐assembled genome (MAG) recovered from the microcosm exhibits ~74% average nucleotide identity with the reported Ca. Methanoperedens spp. that perform Fe(III) reduction linked AOM, thus a novel species Ca. Methanoperedens psychrophilus was proposed. Ca. M. psychrophilus contains the whole suite of CO 2 reductive methanogenic genes presumably involving in AOM via a reverse direction, and comparative genome analysis revealed its unique gene categories: the multi‐heme clusters (MHCs) cytochromes, the S‐layer proteins highly homologous to those recovered from lower temperature environments and type IV pili, those could confer Ca. M. psychrophilus of cold adaptability. Therefore, this work reports the first methanotroph implementing AOM in an alpine wetland.

Abstract Cel.lu.lo.si.ly.ti.ca.ce'ae. N.L. neut. n. Cellulosilyticum a bacterial genus; N.L. fem. pl. n. Cellulosilyticaceae the Cellulosilyticum family. Slightly curved rod‐shaped cells . Gram‐positive cell‐wall structure but stain Gram‐negative. Terminal spores formed. Mesophilic, optimum growth temperature is approximately 40°C. Obligate anaerobic . No microaerophilic or aerobic growth occurs. Produce acetate, ethanol, and/or formate as the major end products, but not butyric or propionic acid. Hydrolyze cellulose and xylan and ferment cellobiose, but not ferment lactate and pyruvate. The predominant fatty acids are C 16:0 (27.1 %), C 14:0 (9.2 %), and iso‐C 16:0 (6.4%). Phylogenetically distant from the family Lachnospriaceae (Clostridum cluster XIVb), a member of the phylum Firmicutes, with less than 87.7% 16S rRNA similarity. Thus far, only one genus Cellulosilyticum is described. DNA G + C content (mol%) : 33–36. Type genus : Cellulosilyticum Cai and Dong 2010, 848 VP . Taxonomic and Nomenclature Notes According to the List of Prokaryotic names with Standing in Nomenclature (LPSN), the taxonomic status of the family Cellulosilyticaceae is: synonym (last update, February 2025) * . Correct name: Lachnospiraceae LPSN classification: Bacteria / Bacillati / Bacillota / Clostridia / Eubacteriales / Lachnospiraceae The family Cellulosilyticaceae can also be recovered in the Genome Taxonomy Database (GTDB) as f__Cellulosilyticaceae (version v220) ** . GTDB classification: d__Bacteria / p__Bacillota_A / c__Clostridia / o__Lachnospirales / f__Cellulosilyticaceae * Meier‐Kolthoff et al. ( 2022 ). Nucleic Acids Res , 50 , D801 – D807 ; DOI: 10.1093/nar/gkab902 ** Parks et al. ( 2022 ). Nucleic Acids Res , 50 , D785 – D794 ; DOI: 10.1093/nar/gkab776

An obligate anaerobic, Gram-staining-negative, mesophilic, cellulolytic bacterium, strain H1T, was isolated from the rumen content of yak. Cells were straight to slightly curved rods, 0.8–1.0×3.0–4.0 μm in size, non-motile and encapsulated with mucous materials. Elliptical and terminal spores that swelled the cells were produced occasionally. The strain grew at 25–45 °C (optimum, 38 °C) and pH 6.0–7.8 (optimum, pH 6.7). Cellulose, cellobiose, xylan, xylose and maltose were used as carbon and energy sources, but not glucose. Products from cellulose and cellobiose fermentation were formic acid, acetic acid, carbon dioxide and trace amounts of ethanol, lactic acid and succinic acid. The genomic DNA G+C content was 33.7±1.2 mol%. The predominant fatty acids were C16 : 0(27.1 %), C14 : 0(9.2 %) and iso-C16 : 0(6.4%). Based on the 16S rRNA gene sequence analysis, strain H1Twas affiliated to the clostridial rRNA cluster XIVb and showed the highest 16S rRNA gene sequence similarity toClostridium lentocellumDSM 5427T(96.0 %). These two strains formed a distinct lineage of the family ‘Lachnospiraceae’. Based on data from this polyphasic taxonomic study, a new genus,Cellulosilyticumgen. nov., is proposed.Cellulosilyticum ruminicolasp. nov. is proposed for strain H1T. The type strain ofCellulosilyticum ruminicolasp. nov. is strain H1T(=CGMCC 1.5065T=JCM 14822T).Clostridium lentocellumwas reclassified in the new genus asCellulosilyticum lentocellumcomb. nov. (type strain RHM5T=ATCC 49066T=DSM 5427T=NCIMB 11756T).