The gut microbiota is a complex community consisting of approximately 3 × 1013 microbial cells from more than 1000 species of bacteria, archaea, and eukaryotes (Proctor et al., 2019). The importance of gut microbiota in maintaining host health is well-established through consistent research findings. The metabolites produced by gut microbiota, such as short-chain fatty acids (SCFAs) (Mann et al., 2024), bile acids (Collins et al., 2023), and various molecular activators of host specific receptors (Arnoldini et al., 2025), play a crucial role in maintaining host health (de Vos et al., 2022). For instance, gut microbiota metabolizes complex carbohydrates that are difficult for the host to digest into SCFAs, including acetate, propionate, and butyrate. They regulate host metabolism (Gao et al., 2009), maintain immune homeostasis (Yang et al., 2020), and improve the nervous system (Xiao et al., 2022; Vicentini et al., 2021), among other activities. Approximately 60% of SCFAs are acetic acid, by which balance the pH of the intestinal lumen and providing energy to the host. SCFAs regulate host immune, metabolism, and intestinal barrier functions through multiple receptor pathways (Hays et al., 2024). Although acetic acid has long been regarded as a benign short-chain fatty acid, recent high-quality cohort studies reveal a more nuanced reality: When particular bacterial consortia overproduce acetic acid, this metabolite shifts from friend to foe, becoming a signaling molecule that results in obesity (Moreno-Navarrete et al., 2018), insulin resistance (Perry et al., 2016), and non-alcoholic steatohepatitis (Park et al., 2021). The main producers of acetic acid in the gut come from specific families within the order Eubacteriales of the phylum Bacillota, such as Lachnospiraceae and Oscillospiraceae (Martin-Gallausiaux et al., 2021; Leth et al., 2023). Lachnospiraceae has been the focus of studies, and the Blautia, a genus within Lachnospiraceae, are closely correlated to modulation of host metabolism, immune, and inflammation (Chanda et al., 2024; Liu et al., 2021a). The potential functions of Oscillospiraceae members are not well-documented, except the popular species Faecalibacterium prausnitzii (Miquel et al., 2013). The family Lachnospiraceae, on the other hand, has 217 species, according to LPSN records (https://lpsn.dsmz.de/family/lachnospiraceae), including 27 species in the Blautia (https://lpsn.dsmz.de/genus/blautia). Oscillospiraceae (https://lpsn.dsmz.de/family/oscillospiraceae) remains relatively sparsely populated, with only 137 species names validated to date. Still, previous study (Liu et al., 2022a) revealed that many members of Lachnospiraceae and Oscillospiraceae remain unclassified and need to be formally described.

In this study, we isolated and characterized two new strains HA2173T and HA2174T. Based on the results of phylogenetic analysis, phenotypic and chemotaxonomic characteristics, strains HA2173T and HA2174T were identified as new species from the genus Zongyangia of the family Oscillospiraceae and from the genus Blautia of the family Lachnospiraceae, respectively. Both strains produced acetic acids as the main fermentative products, thus they are named Zongyangia acetica and Blautia acetica. Because the Oscillospiraceae and Lachnospiraceae families have emerged as critical modulators of host physiology, the isolation and characterization of these novel bacterial species provide a timely reservoir for future studies dissecting their precise roles in health and disease.