Outbreaks of diseases in farmed fish remain a recurring problem despite the development of vaccines and improved hygiene standards on aquaculture farms. One commonly observed bacterial disease in tropical aquaculture of the South-East Asian region is tenacibaculosis, which is attributed to members of the Bacteroidetes genus Tenacibaculum, most notably T. maritimum. The impact of tenacibaculosis on fish microbiota remains poorly understood. In this study, we analysed the microbiota of different tissue types of commercially reared Asian seabass (Lates calcarifer) that showed symptoms of tenacibaculosis and compared the microbial communities to those of healthy and experimentally infected fish that were exposed to diseased farm fish. The microbiota of diseased farm fish was dominated by Proteobacteria (relative abundance±standard deviation, 74.5%±22.8%) and Bacteroidetes (18.07%±21.7%), the latter mainly comprised by a high abundance of Tenacibaculum species (17.6%±20.7%).In healthy seabass Proteobacteria had also highest relative abundance (48.04%±0.02%), but Firmicutes (34.2%±0.02%) and Fusobacteria (12.0%±0.03%) were the next two major constituents. Experimentally infected fish developed lesions characteristic for tenacibaculosis, but the microbiota was primarily dominated by Proteobacteria (90.4%±0.2%) and Firmicutes (6.2%±0.1%). The relative abundance of Tenacibaculum species in experimentally infected fish was significantly lower than in the commercially reared diseased fish and revealed a higher prevalence of different Tenacibaculum species. One strain was isolated and is described here as sp. nov. Tenacibaculum singaporense TLL-A1 T (=DSM 106434 T , KCTC 62393 T ). The genome of T. singaporense was sequenced and compared to those of T. maritimum DSM 17995 T and the newly sequenced T. mesophilum DSM 13764 T .

Methanobrevibacter and Methanosphaera species represent some of the most prevalent methanogenic archaea in the gastrointestinal tract of animals and humans and play an important role in this environment. The aim of this study was to identify genomic features that are shared or specific for members of each genus with a special emphasis of the analysis on the assimilation of nitrogen and acetate and the utilization of methanol and ethanol for methanogenesis. Here, draft genome sequences of Methanobrevibacter thaueri strain DSM 11995T, Methanobrevibacter woesei strain DSM 11979T, and Methanosphaera cuniculi strain 4103T are reported and compared to those of 16 other Methanobrevibacter and Methanosphaera genomes, including genomes of the 13 currently available types of strains of the two genera. The comparative genome analyses indicate that among other genes, the absence of molybdopterin cofactor biosynthesis is conserved in Methanosphaera species but reveals also that the three species share a core set of more than 300 genes that distinguishes the genus Methanosphaera from the genus Methanobrevibacter. Multilocus sequence analysis shows that the genus Methanobrevibacter can be subdivided into clades, potentially new genera, which may display characteristic specific metabolic features. These features include not only the potential ability of nitrogen fixation and acetate assimilation in a clade comprised of Methanobrevibacter species from the termite gut and Methanobrevibacter arboriphilus strains but also the potential capability to utilize ethanol and methanol in a clade comprising Methanobrevibacter wolinii strain DSM 11976T, Mbb. sp. AbM4, and Mbb. boviskoreani strain DSM 25824T.

Three bacterial strains, C9, H5 and TLL-A3, were isolated from fecal pellets of conventionally raised C57BL/6J mice. Analysis of 16S rRNA genes indicated that the strains belonged to the Muribaculaceae , and shared 91.6–99.9 % sequence identity with the recently described Duncaniella muris DSM 103720T. Genome-sequencing of the isolates was performed to compare average nucleotide identities (ANI) between strains. The ANI analysis revealed that all isolates shared highest ANI with D. muris DSM 103720T, with strain C9 being most similar (ANI: 98.0 %) followed by strains H5 (ANI: 76.4 %) and TLL-A3 (ANI: 74.4 %). Likewise, digital DNA–DNA hybridization (dDDH) indicated high similarity of strain C9 (dDDH: 86.6 %) to D. muris DSM 103720T, but strains H5 and TLL-A3 showed lower similarity (dDDH <35 %) to either of the three type species of the Muribaculaceae ( Muribaculum intestinale DSM 28989T , Paramuribaculum intestinale DSM 100749T, D. muris DSM 103720T). MK-10 and MK-11 were abundant in all three isolates, but concentrations varied between species. Based on genotypic, phylogenetic and phenotypic differences, the strains TLL-A3 and H5 are considered to represent novel species of the genus Duncaniella , for which the names Duncaniella freteri sp. nov., and Duncaniella dubosii sp. nov., are proposed. The respective type strains are TLL-A3T (=DSM 108168T=KCTC 15769T), and H5T (=DSM 107170T=KCTC 15734T). Strain C9 reveals limited sequence dissimilarity and minor differences in morphological properties with Duncaniella muris DSM 103720T and is therefore proposed to belong to the same species. The respective strain is C9 (=DSM 107165=KCTC 15733).

An anaerobic bacterial strain, named TLL-A4T, was isolated from fecal pellets of conventionally raised C57BL/6J mice. Analysis of the 16S rRNA gene indicated that the strain belongs to the phylum Bacteroidetes and, more specifically, to the recently proposed Muribaculaceae (also known as S24-7 clade or Candidatus Homeothermaceae). Strain TLL-A4T’s 16S rRNA gene shared 92.8 % sequence identity with the type strain of the only published species of the genus Muribaculum , Muribaculum intestinale DSM 28989T. Genome-sequencing of TLL-A4T was performed to compare average amino acid identity (AAI) value and percentage of conserved proteins (POCP) between both strains. The AAI analysis revealed that strain TLL-A4T had high identity (69.8 %) with M. intestinale DSM 28989T, while the POCP was 56 %. These values indicate that strain TLL-A4T could be considered a member of the genus Muribaculum but not belonging to the species M. intestinale . Quinone analysis indicated MK10 (63 %) and MK11 (32 %) as major quinones in the membrane, while MK9 was only present as a minor component (5 %). The main cellular fatty acid was anteiso-C15 : 0 (42.8 %); summed feature 11 (17.5 %), C15 : 0 iso (13.4 %), C18 : 1 ω9c (5.6 %), C16.0 3-OH (4.5 %) and C15 : 0 (4.2 %) were detected in minor amounts. Analysis of enzyme activities using the API 32A and API 20A kits indicated major differences between strain TLL-A4T and Muribaculum intestinale DSM 28989T. Based on genotypic, phylogenetic and phenotypic differences, strain TLL-A4T is considered to represent a novel species of the genus Muribaculum , for which the name Muribaculum gordoncarteri sp. nov. is proposed. The type strain is TLL-A4T (=DSM 108194T=KCTC 15770T).

Dietary changes are known to alter the composition of the gut microbiome. However, it is less understood how repeatable and reversible these changes are and how diet switches affect the microbiota in the various segments of the gastrointestinal tract. Here, a treatment group of conventionally raised laboratory mice is subjected to two periods of western diet (WD) interrupted by a period of standard diet (SD) of the same duration. Beta-diversity analyses show that diet-induced microbiota changes are largely reversible (q = 0.1501; PERMANOVA, weighted-UniFrac comparison of the treatment-SD group to the control-SD group) and repeatable (q = 0.032; PERMANOVA, weighted-UniFrac comparison of both WD treatments). Furthermore, we report that diet switches alter the gut microbiota composition along the length of the intestinal tract in a segment-specific manner, leading to gut segment-specific Firmicutes/Bacteroidota ratios. We identified prevalent and distinct Amplicon Sequencing Variants (ASVs), particularly in genera of the recently described Muribaculaceae, along the gut as well as ASVs that are differentially abundant between segments of treatment and control groups. Overall, this study provides insights into the reversibility of diet-induced microbiota changes and highlights the importance of expanding sampling efforts beyond the collections of fecal samples to characterize diet-dependent and segment-specific microbiome differences.