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The marine archaeon Methanosarcina acetivorans contains a putative NAD + -independent d-lactate dehydrogenase (D-iLDH/glycolate oxidase) encoded by the MA4631 gene, belonging to the FAD-oxidase C superfamily. Nucleotide sequences similar to MA4631 gene, were identified in other methanogens and Firmicutes with >90 and 35-40% identity, respectively. Therefore, the lactate metabolism in M. acetivorans is reported here. Cells subjected to intermittent pulses of oxygen (air-adapted; AA-Ma cells) consumed lactate only in combination with acetate, increasing methane production and biomass yield. In AA-Ma cells incubated with d-lactate plus [14C]-l-lactate, the radioactive label was found in methane, CO2 and glycogen, indicating that lactate metabolism fed both methanogenesis and gluconeogenesis. Moreover, d-lactate oxidation was coupled to O2-consumption which was sensitive to HQNO; also, AA-Ma cells showed high transcript levels of gene dld and those encoding subunits A (MA1006) and B (MA1007) of a putative cytochrome bd quinol oxidase, compared to anaerobic control cells. An E. coli mutant deficient in dld complemented with the MA4631 gene, grew with d-lactate as carbon source and showed membrane-bound d-lactate:quinone oxidoreductase activity. The product of the MA4631 gene is a FAD-containing monomer showing activity of iLDH with preference to d-lactate. The results suggested that air adapted M. acetivorans is able to co-metabolize lactate and acetate with associated oxygen consumption by triggering the transcription and synthesis of the D-iLDH and a putative cytochrome bd: methanophenazine (quinol) oxidoreductase. Biomass generation and O2 consumption, suggest a potentially new oxygen detoxification mechanism coupled to energy conservation in this methanogen.

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A challenge in the study of gastrointestinal microbiota (GITm) is the validation of the genomic data with metabolic studies of the microbial communities to understand how the microbial networks work during health and sickness. To gain insights into the metabolism of the GITm, feces from healthy and sick rats with cancer were inoculated in a defined synthetic medium directed for anaerobic prokaryote growth (INC-07 medium). Significant differences between cultures of healthy and sick individuals were found: 1) the consumption of the carbon source and the enzyme activity involved in their catabolism (e.g., sucrase, lactase, lipases, aminotransferases, and dehydrogenases); 2) higher excretion of acetic, propionic, isobutyric, butyric, valeric, and isovaleric acids; 3) methane production; 4) ability to form biofilms; and 5) up to 500 amplicon sequencing variants (ASVs) identified showed different diversity and abundance. Moreover, the bowel inflammation induced by cancer triggered oxidative stress, which correlated with deficient antioxidant machinery (e.g., NADPH-producing enzymes) determined in the GITm cultures from sick individuals in comparison with those from control individuals. Altogether, the data suggested that to preserve the microbial network between bacteria and methanogenic archaea, a complete oxidation of the carbon source may be essential for healthy microbiota. The correlation of 16S rRNA gene metabarcoding between cultures and feces, as well as metabolomic data found in cultures, suggest that INC-07 medium may be a useful tool to understand the metabolism of microbiota under gut conditions.

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Tepache is a native beverage from Mexico, which is usually elaborated with pineapple shells, brown cane sugar and is fermented naturally. Beneficial health effects have been attributed to its consumption; however, the total ecosystem of this beverage including chemicals (substrates for microbial growth, prebiotics, etc) and microbiota (probiotics), and potential functionality had not been studied. In this work, the analysis of the tepache beverage for its physicochemical characteristics, as well as its structure of microbial communities and the predictive metabolic functionalities was carried out. Chemical characterization was performed via enzymatic and GC-MS methods. The bacterial and fungal communities were identified by using 16S rRNA and ITS metabarcoding through Illumina MiSeq 2 × 300. The metabolic potential was predicted by in silico tools. This research showed that after 72 h of fermentation, the tepache physicochemical characteristics shifted to 9.5 Brix degrees and acidic pH. The content of ethanol, acetic and L-lactic acid increased significantly from 0.83 ± 0.02 to 3.39 ± 0.18 g/L, from 0.38 ± 0.04 to 0.54 ± 0.04 g/L and from 1.42 ± 0.75 to 8.77 ± 0.34 g/L, respectively. While, the total sugars was decreased from 123.43 ± 2.01 to 84.70 ± 2.34 g/L. The microbial diversity analysis showed a higher richness of bacterial communities and increased fungal evenness at the end of fermentation. At 72 h of fermentation the microbial community was dominated by Lactobacillus, Leuconostoc, Acetobacter and Lactococcus bacterial genera. As for the fungal community, Saccharomyces, Gibberella, Zygosaccharomyces, Candida, Meyerozyma, Talaromyces, Epicoccum and Kabatiella were found to be in most abundance. The predicted functionality profile evidenced a close-fitting relationship between fungal communities at 0 h with the bacterial communities at 72 h of fermentation. The metabolic potential showed that glycolysis and citrate cycle metabolism were predominant for fungal community, while glycolysis, fructose and tricarboxylic acid metabolism were more representative for the bacterial core. Tepache fermentation mainly occurred at two temporal successions. First, a lactic acid and ethanol fermentation dominated by lactic acid bacteria and yeast, and then an increase in acetogenic bacteria. This study revealed for the first time the physicochemical, microbiological changes and predictive functionality that are involved during tepache fermentation. These findings contributed to the knowledge of important microbial sources and could be essential to future efforts in manufacturing process. In addition, this work could help to analyze the health benefits that are empirically attributed to it by consumers.

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El Chichón volcano is one of the most active volcanoes in Mexico. Previous studies have described its poly-extreme conditions and its bacterial composition, although the functional features of the complete microbiome have not been characterized yet. By using metabarcoding analysis, metagenomics, metabolomics and enzymology techniques, the microbiome of the crater lake was characterized in this study. New information is provided on the taxonomic and functional diversity of the representative Archaea phyla, Crenarchaeota and Euryarchaeota, as well as those that are representative of Bacteria, Thermotogales and Aquificae. With culture of microbial consortia and with the genetic information collected from the natural environment sampling, metabolic interactions were identified between prokaryotes, which can withstand multiple extreme conditions. The existence of a close relationship between the biogeochemical cycles of carbon and sulfur in an active volcano has been proposed, while the relationship in the energy metabolism of thermoacidophilic bacteria and archaea in this multi-extreme environment was biochemically revealed for the first time. These findings contribute towards understanding microbial metabolism under extreme conditions, and provide potential knowledge pertaining to "microbial dark matter", which can be applied to biotechnological processes and evolutionary studies.

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Mango (Mangifera indica L.) peel and pulp are a source of dietary fiber (DF) and phenolic compounds (PCs) that constituent part of the indigestible fraction (IF). This fraction reaches the colon and acts as a carbon and energy source for intestinal microbiota. The effect of mango IF on intestinal microbiota during colonic fermentation is unknown. In this study, the isolated IF of a novel 'Ataulfo' mango-based bar (snack) UV-C irradiated and non-irradiated (UVMangoB and MangoB) were fermented. Colonic fermentation occurred in vitro under chemical-enzymatic, semi-anaerobic, batch culture and controlled pH colonic conditions. Changes in the structure of fecal microbiota were analyzed by 16s rRNA gene Illumina MiSeq sequencing. The community´s functional capabilities were determined in silico. The MangoB and UVMangoB increased the presence of Faecalibacterium, Roseburia, Eubacterium, Fusicatenibacter, Holdemanella, Catenibacterium, Phascolarctobacterium, Buttiauxella, Bifidobacterium, Collinsella, Prevotella and Bacteroides genera. The alpha indexes showed a decrease in microbial diversity after 6 h of colonic fermentation. The coordinates analysis indicated any differences between irradiated and non-irradiated bar. The metabolic prediction demonstrated that MangoB and UVMangoB increase the microbiota carbohydrate metabolism pathway. This study suggests that IF of mango-based bar induced beneficial changes on microbial ecology and metabolic pathway that could be promissory to prevention or treatment of metabolic dysbiosis. However, in vivo interventions are necessary to confirm the interactions between microbiota modulating and intestinal beneficial effects.

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