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Effect of Short-Chain Fatty Acids Produced by Probiotics
Published in Marcela Albuquerque Cavalcanti de Albuquerque, Alejandra de Moreno de LeBlanc, Jean Guy LeBlanc, Raquel Bedani, Lactic Acid Bacteria, 2020
Milena Fernandes da Silva, Meire dos Santos Falcão de Lima, Attilio Converti
Patients affected by inflammatory bowel and autoimmune diseases, type 2 diabetes or obesity often exhibit abnormal reduction of levels of SCFAs in gut or SCFA-producing gut bacteria (Rivière et al. 2016, Sun et al. 2017, Hu et al. 2018). Nagpal et al. (2018) recently suggested that such perturbations may be the result of a reduction in the population of gut bacteria that grow in syntrophy with SCFA producers or of an increase in the release of harmful compounds by either the gastrointestinal tract or other microbes. Thus, the following sessions will provide some examples of SCFA regulatory functions on host physiology, highlighting the functional role of these acids in improving human health, with special emphasis on obesity and cancer.
Lifestyle Influences on the Microbiome
Published in David Perlmutter, The Microbiome and the Brain, 2019
Sulfur-reducing bacteria (SRB) consume hydrogen in the generation of H2S, an autacoid with both pro-27,28 and anti-inflammatory29 signaling attributes. Like Archea, SRB are found in about half of human stool specimens30 and attach directly to colonic mucosa.30 Although sulfate-reducing activity is found in many phyla, the dominant SRB in the human colon are members of the genus Desulfovibrio in the phylum Proteobacteria.31 Dietary sulfur is found in ingested protein and in sulfate and sulfite preservatives added to a variety of foods, like bread, preserved meat, dried fruit, and wine. Sulfate is also present in the common food additive carrageenan. Even without food, sulfur is present in sulfated glycans present in host-derived colonic mucus. Unlike Archaea, which through their syntrophism with Ruminococcus grow well in a carbohydrate-rich environment, Desulfovibrio piger, is syntrophic with Bacteroides species like B. thetaiotamicron and thrives when animals are fed a diet high in sugar and fat and low in complex polysaccharides.32 When the diet lacks complex polysaccharides, Bacteroides-derived sulfatases liberate sulfates from mucosal glycans,33 helping D. piger fill its appetite for sulfur.
Addition of Trichocladium canadense to an anaerobic membrane bioreactor: evaluation of the microbial composition and reactor performance
Published in Biofouling, 2021
Hadi Fakhri, Duygu Nur Arabacı, İlayda Dilara Ünlü, Cigdem Yangin-Gomec, Suleyman Ovez, Sevcan Aydin
Biofilms consist of mixed microbial communities. Archaea, especially methanogens, form syntrophic relations with bacteria and have been found together with bacteria in biofilms in various natural environments, from natural bodies of water to human bodies (van Wolferen et al. 2018). Given the nature of membrane bioreactors, the high surface area provides increased attachment and growth of microorganisms on the membrane. In this study, samples from the cake layer were analyzed through 16S rRNA gene sequencing (Figure 5). The results indicated that the archaeal community in the biofilm layer was significantly enriched in the TC reactor, making up 0.7% of the total microbial community compared with the relative abundances of 0.1% and 0.06% in the C1 and C2 reactors, respectively. Similar to the sludge samples, the biofilm cake layer showed increased archaeal diversity in the presence of T. canadense with least diversity in the C1 reactor. This may be due to the decrease in antagonistic microbial species, while the sub-MIC of antibiotics also promoting biofilm growth, therefore increasing the total abundance of microorganisms.
Enabling rational gut microbiome manipulations by understanding gut ecology through experimentally-evidenced in silico models
Published in Gut Microbes, 2021
Juan P. Molina Ortiz, Dale D. McClure, Erin R. Shanahan, Fariba Dehghani, Andrew J. Holmes, Mark N. Read
Intricate metabolic interactions take place between gut microbes. Diverse ecological relationships, such as cross-feeding (mutualism), amensalism, and competition coexist in the gut to shape the microbiome and its metabolic output. Cross-feeding has been extensively studied owing to its scope for expanding a strain’s growth niche. For instance, in co-culture, Ruminococcus bromii produces formate which B. hydrogenotrophica consumes, and B. hydrogenotrophica reciprocates with panthothenate which R. bromii requires for optimal growth but cannot synthesize.100 This relationship also involves hydrogen utilization by B. hydrogenotrophica as described above. Concomitantly, R. bromii and B. hydrogenotrophica compete for the vitamin thiamine in this context, exemplifying how complex interactions in the gut can be. Microbes form a complex web of interactions and variations in microbial membership or activity can trigger a cascade of effects across the network. The units of biological activity in a community are not necessarily cells or strains – syntrophic dependencies mean multi-organism networks are more appropriate for modeling some outputs.
Interactions of commensal and pathogenic microorganisms with the mucus layer in the colon
Published in Gut Microbes, 2020
Rui Cai, Chen Cheng, Jianwei Chen, Xiaoqiang Xu, Chao Ding, Bing Gu
To colonize the mucus layer, pathogenic bacteria have to compete with the commensal microbiota to harvest nutrients for their expansion. One method is to exploit the oligosaccharides released from the mucins by saccharolytic members of the microbiota. For instance, Bacteroides thetaiotaomicron, widely used as a model of Bacteroides to investigate syntrophic links, has sialidase activity to harvest sialic acid but lacks the catabolic pathway for its utilization. Therefore, the sialic acid released by B. thetaiotaomicron can be catabolized by C. difficile and S. typhimurium to promote pathogen growth and expansion.53B. thetaiotaomicron can also cleave fucose from host glycans via multiple enzymes, and free fucose can be used as another carbon source for S. typhimurium.53 Fucose is also a signaling molecule to regulate the expression of EHEC’s virulence repertoire.78 EHEC aims to achieve a particular niche by closely adhering to the intestinal enterocytes and competes with the commensal E. coli for nutrients. EHEC can also use specific sugars that commensal E. coli cannot utilize, such as galactose, mannose, hexuranates and ribose.79