The methanogenic strain Mx-05^T was isolated from the human fecal microbiome. A phylogenetic analysis based on the 16S rRNA gene and protein marker genes indicated that the strain is affiliated with the order Methanomassiliicoccales. It shares 86.9% 16S rRNA gene sequence identity with Methanomassiliicoccus luminyensis, the only member of this order previously isolated. The cells of Mx-05^T were non-motile cocci, with a diameter range of 0.4–0.7 μm. They grew anaerobically and reduced methanol, monomethylamine, dimethylamine, and trimethylamine into methane, using H₂ as an electron donor. H₂/CO₂, formate, ethanol, and acetate were not used as energy sources. The growth of Mx-05^T required an unknown medium factor(s) provided by Eggerthella lenta and present in rumen fluid. Mx-05^T grew between 30 °C and 40 °C (optimum 37 °C), over a pH range of 6.9–8.3 (optimum pH 7.5), and between 0.02 and 0.34 mol.L⁻¹ NaCl (optimum 0.12 mol.L⁻¹ NaCl). The genome is 1.67 Mbp with a G+C content of 55.5 mol%. Genome sequence annotation confirmed the absence of the methyl branch of the H₄MPT Wood–Ljungdahl pathway, as described for other Methanomassiliicoccales members. Based on an average nucleotide identity analysis, we propose strain Mx-05^T as being a novel representative of the order Methanomassiliicoccales, within the novel family Methanomethylophilaceae, for which the name Methanomethylophilus alvi gen. nov, sp. nov. is proposed. The type strain is Mx-05^T (JCM 31474T).

Bacterial vaginosis (BV) is characterized by the presence of a polymicrobial biofilm where Gardnerella vaginalis plays a key role. Previously, we demonstrated that Saccharomyces cerevisiae CNCM (French National Collection of Cultures of Microorganisms) I-3856 is helpful in resolving experimental simulated BV in mice. In this study, we analyzed its capacity to affect G. vaginalis biofilms and to potentiate the activity of standard antimicrobial agents. We also investigated the anti-biofilm activity of Lacticaseibacillus rhamnosus GG (ATCC 53103), a well-known strain for its intestinal healthy benefits. Biofilm biomass was assessed by crystal violet staining, and G. vaginalis viability was assessed by a colony forming unit (CFU) assay. Here, for the first time, we demonstrated that S. cerevisiae CNCM I-3856 as well as L. rhamnosus GG were able (i) to significantly inhibit G. vaginalis biofilm formation, (ii) to markedly reduce G. vaginalis viability among the biomass constituting the biofilm, (iii) to induce disaggregation of preformed biofilm, and (iv) to kill a consistent amount of bacterial cells in a G. vaginalis preformed biofilm. Furthermore, S. cerevisiae CNCM I-3856 strongly potentiates the metronidazole effect on G. vaginalis biofilm viability. These results suggest that S. cerevisiae CNCM I-3856 as well as L. rhamnosus GG could be potential novel therapeutic agents against bacterial vaginosis.

Saccharomyces cerevisiae (SC), a yeast with an extensive history in food and beverage fermentations, is increasingly acknowledged for its multifaceted application in promoting and benefiting all aspects of a ‘One Health’ approach, including the prevention and control of zoonoses. For instance, SC contributes to environmentally sustainable agricultural practices through the reduced use of toxic agents, thus minimizing air and soil pollution while enhancing crop quality. Additionally, this versatile yeast can improve the health of domestic and farm animals, leading to more efficient and sustainable food production, while fostering synergistic impacts across environmental, animal, and human health spheres. Moreover, SC directly applies benefits to human health by promoting improved nutrition, improving gut health through probiotics, as an alternative to antibiotics, and treating gastric disorders. By aligning with several Sustainable Development Goals (SDGs), SC is vital in advancing global health and well-being, environmental sustainability, and responsible consumption and production. This entry illustrates the numerous benefits of SC and highlights its significant impact on a global ‘One Health’ scale, promoting the achievement of SDGs through its unique characteristics and deeper understanding of its contribution to the One Health concept.

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by its main symptom, visceral hypersensitivity (VH), which is aggravated by stress. Gut–brain interactions and gut bacteria may alleviate IBS symptoms, including VH. γ‐amino butyric acid (GABA), produced notably by lactic acid bacteria (LAB), shows promising result in IBS symptoms treatment. In bacteria, GABA is generated through glutamate decarboxylase (GAD) metabolism of L‐glutamic acid, maintaining intracellular pH. In mammals, GABA acts as an inhibitory neurotransmitter, modulating pain, stress, and anxiety. Therefore, utilizing GABA‐producing LAB as a therapeutic approach might be beneficial. Our previous work showed that a GABA‐producing Lactococcus lactis strain, NCDO2118, reduced VH induced by acute stress in rats after a 10‐day oral treatment. Here, we identified the strain CNCM I‐5388, with a four‐fold higher GABA production rate under the same conditions as NCDO2118. Both strains shared 99.1% identical GAD amino acid sequences and in vitro analyses revealed the same optimal pH for GAD activity; however, CNCM I‐5388 exhibited 17 times higher intracellular GAD activity and increased resistance to acidic pH. Additionally, in vivo experiments have demonstrated that CNCM I‐5388 has faster anti‐VH properties in rats compared with NCDO2118, starting from the fifth day of treatment. Finally, CNCM I‐5388 anti‐VH effects partially persisted after 5‐day treatment interruption and after a single oral treatment. These findings highlight CNCM I‐5388 as a potential therapeutic agent for managing VH in IBS patients.

Irritable bowel syndrome (IBS) is a multifactorial disorder of the gut‐brain axis, characterized by visceral hypersensitivity (VH). Psychobiotics, through GABA synthesis, are good candidates to alleviate gastrointestinal discomfort. Here, we analyzed the GABA‐producer Lactococcus lactis CNCM I‐5388 as an active‐enzyme postbiotic to relieve VH mediated by psychological stress. L. lactis CNCM I‐5388 was inactivated by ethanol while maintaining its glutamate decarboxylase (GAD) activity. This EtOH‐treated nonviable form was given daily orally for 1, 5, or 10 days to female Wistar rats in comparison with viable L. lactis CNCM I‐5388 or vehicle. Visceral sensitivity was measured by electromyography before and after partial restraint stress (PRS). GABA was quantified in the stomach collected from rats and in the gastric compartment of TIM‐1 human gut model in fed state. A daily treatment for 5 and 10 days by L. lactis CNCM I‐5388 both in its viable and nonviable forms counteracted VH promoted by PRS. However, only viable L. lactis CNCM I‐5388 tended to reduce VH after a single administration. After 5‐day treatment, only under PRS conditions, the production of GABA within the stomach was enhanced in rats treated with viable or nonviable L. lactis CNCM I‐5388. This increase was confirmed by using the TIM‐1 human gut model. We found that a postbiotic with an active‐GAD enzyme of L. lactis CNCM I‐5388, similarly to its viable psychobiotic form, exerts anti‐VH properties in an IBS‐like rat model. These effects are associated with GABA production in the stomach where the low pH promotes GAD activity.

Periodontal disease (PD) is one of the most widespread oral inflammatory diseases in dogs, with the potential to cause systemic consequences. The purpose of this study was to evaluate the inhibitory potential of yeast-derived postbiotics and probiotic bacterial strains by using a previously developed in vitro biofilm model mimicking canine PD-associated biofilm including five bacterial species: Neisseria zoodegmatis, Corynebacterium canis, Porphyromonas cangingivalis, Peptostreptococcus canis, and Enterococcus faecalis. After we confirmed the presence of these five bacterial species by employing Fluorescence In Situ Hybridization, the biofilm inhibitory and eradication activity of 11 yeast-derived postbiotics and probiotic bacterial strains, as well as selected dual biotic combinations, against the polymicrobial biofilm were determined using a modified version of the Calgary Biofilm Pin Lid Device and the crystal violet method; additionally, hemolytic activity was evaluated using canine red blood cells. The results show that the inhibitory activity against the polymicrobial PD biofilm ranged from 0% to 22.55%, and eradication ability varied between 0% and 17.28%; however, when combined, the biotics achieved a maximum inhibition rate of 71%. Probiotic strain BC-05 exhibited the lowest in vitro hemolytic activity. Overall, based on the results, four yeast-derived postbiotics and one probiotic bacterial strain were selected as promising candidates for further evaluation, aiming at in vivo application.