Anaerozeibacter quisquiliarum gen. nov., sp. nov., a novel mesophilic bacterium isolated from a laboratory-scale methanogenic landfill bioreactor digesting maize, and proposal of Anaerozeibacteraceae fam. nov., representing a new family within the order Eubacteriales.

Bacteria involved in the anaerobic degradation of lignocellulosic waste in landfill sites play crucial roles in carbon turnover and biogas generation. In this study, we isolated and characterized a novel anaerobic bacterium, strain meth-B3ᵀ, from a laboratory-scale methanogenic bioreactor fed with maize-based biomass. Cells were Gram-stain-negative, non-spore-forming, motile rods with optimal growth at 35 °C, pH 7.0 and 0.7% sodium chloride (NaCl). Strain meth-B3ᵀ utilized a broad spectrum of carbohydrates, amino acids and organic acids, including glucose, cellobiose, glycerol, sucrose, maltose and various nitrogenous compounds. It fermented glucose into acetate, butyrate, lactate, propionate, valerate and ethanol. Whole-genome sequencing revealed a 3.8 Mbp genome with a G+C content of 62.65 mol%. Phylogenomic analyses based on 16S rRNA and conserved marker genes placed strain meth-B3ᵀ within the order Eubacteriales, forming a distinct clade from other known families. Comparative genomic metrics (average nucleotide identity, ≤69.4%; average amino acid identity, ≤54.2%; percentage of conserved protein, ≤35.2%) confirmed that strain meth-B3ᵀ represents a novel genus and family. Notably, carbohydrate-active enzyme and Clusters of Orthologous Groups (COG) functional profiling revealed an extensive suite of enzymes with potential activities against cellulose, xylan, starch and other maize-derived polymers, underscoring its ecological and biotechnological relevance in biomass degradation and biogas production. On the basis of genotypic and phenotypic distinctions, we propose the name Anaerozeibacter quisquiliarum gen. nov., sp. nov., with strain meth-B3ᵀ (=DSM 112769ᵀ=ATCC TSD-269ᵀ) being the type strain, and designate Anaerozeibacteraceae fam. nov. within the order Eubacteriales to accommodate this lineage.