pH and Peptide Supply Can Radically Alter Bacterial Populations and Short-Chain Fatty Acid Ratios within Microbial Communities from the Human Colon

Abstract

The effects of changes in the gut environment upon the human colonic microbiota are poorly understood. The response of human fecal microbial communities from two donors to alterations in pH (5.5 or 6.5) and peptides (0.6 or 0.1%) was studied here in anaerobic continuous cultures supplied with a mixed carbohydrate source. Final butyrate concentrations were markedly higher at pH 5.5 (0.6% peptide mean, 24.9 mM; 0.1% peptide mean, 13.8 mM) than at pH 6.5 (0.6% peptide mean, 5.3 mM; 0.1% peptide mean, 7.6 mM). At pH 5.5 and 0.6% peptide input, a high butyrate production coincided with decreasing acetate concentrations. The highest propionate concentrations (mean, 20.6 mM) occurred at pH 6.5 and 0.6% peptide input. In parallel, major bacterial groups were monitored by using fluorescence in situ hybridization with a panel of specific 16S rRNA probes. Bacteroides levels increased from ca. 20 to 75% of total eubacteria after a shift from pH 5.5 to 6.5, at 0.6% peptide, coinciding with high propionate formation. Conversely, populations of the butyrate-producing Roseburia group were highest (11 to 19%) at pH 5.5 but fell at pH 6.5, a finding that correlates with butyrate formation. When tested in batch culture, three Bacteroides species grew well at pH 6.7 but poorly at pH 5.5, which is consistent with the behavior observed for the mixed community. Two Roseburia isolates grew equally well at pH 6.7 and 5.5. These findings suggest that a lowering of pH resulting from substrate fermentation in the colon may boost butyrate production and populations of butyrate-producing bacteria, while at the same time curtailing the growth of Bacteroides spp.Microbial metabolism in the colon has an important impact on health and is strongly influenced by the amount and type of dietary components that survive small intestinal digestion. Short-chain fatty acids (SCFA) arising from microbial fermentation provide energy sources for the colonic epithelium, and butyrate in particular exerts important effects on cell differentiation and gut health (2,6,30,44,48,50). Products of microbial fermentation, however, can also be toxic or carcinogenic (21). Shifts in microbial community structure caused by diet (32) also have the potential to influence interactions between gut microbes, gut epithelial cells, and the immune system (10,28,40).Conditions for bacterial growth and metabolism in the human large intestine vary with diet and with location in the colon (8, 9, 25, 38, 52). We have little reliable information, however, on the likely impact of dietary and environmental factors on the microbial community of the human colon. The pH of the gut lumen is likely to be a key factor. Several reports indicate that a slightly acidic pH can occur in the proximal colon, increasing distally (4, 38, 46). A major factor tending to reduce colonic pH is the production of SCFA by microbial fermentation of dietary carbohydrate energy sources, including prebiotics, that are digestible by gut microorganisms but not by host enzymes (4,18,20). Another key factor that must...

Supplementation of enzyme-treated soy protein saves dietary protein and promotes digestive and absorptive ability referring to TOR signaling in juvenile fish

“…The negative response on AKP gene expression in the current study might be related to the microorganism population. It has been confirmed that peptide supported the growth of Bacteroides in the distal intestine of human (Walker et al 2005). Furthermore, Bacteroides could secrete lipopolysaccharide in human gut (Conlon and Bird 2015).…”

Phylogenetic distribution of three pathways for propionate production within the human gut microbiota

“…In addition to the type of carbohydrate available to the microbiota, other factors also have to be considered with regard to propionate production in the gut. Thus, pH is an important determinant in the competition between Bacteroidetes and Firmicutes (Walker et al, 2005;Duncan et al, 2009), and the level of propionate production in Bacteroidetes is dependent on carbon dioxide levels (Macfarlane and Gibson, 1997).…”

Production of Butyrate from Lactate by a Newly Isolated Clostridium sp. BPY5

“…This suggested that production of butyrate was limited by the availability of lactate (electron donor) rather than by that of acetate (electron acceptor). In addition, pH is reported to alter the end products of fermentation [37]. For example, the metabolic pathway of xylose fermentation by Clostridium tyrobutyricum switches from butyrate production to lactate and acetate formation when pH decreases from 6.3 to 5.7 or lower [38].…”