Document Detail

The role of pH in determining the species composition of the human colonic microbiota.
MedLine Citation:
PMID:  19397676     Owner:  NLM     Status:  MEDLINE    
The pH of the colonic lumen varies with anatomical site and microbial fermentation of dietary residue. We have investigated the impact of mildly acidic pH, which occurs in the proximal colon, on the growth of different species of human colonic bacteria in pure culture and in the complete microbial community. Growth was determined for 33 representative human colonic bacteria at three initial pH values (approximately 5.5, 6.2 and 6.7) in anaerobic YCFA medium, which includes a mixture of short-chain fatty acids (SCFA) with 0.2% glucose as energy source. Representatives of all eight Bacteroides species tested grew poorly at pH 5.5, as did Escherichia coli, whereas 19 of the 23 gram-positive anaerobes tested gave growth rates at pH 5.5 that were at least 50% of those at pH 6.7. Growth inhibition of B. thetaiotaomicron at pH 5.5 was increased by the presence of the SCFA mix (33 mM acetate, 9 mM propionate and 1 mM each of iso-valerate, valerate and iso-butyrate). Analysis of amplified 16S rRNA sequences demonstrated a major pH-driven shift within a human faecal bacterial community in a continuous flow fermentor. Bacteroides spp. accounted for 27% of 16S rRNA sequences detected at pH 5.5, but 86% of sequences at pH 6.7. Conversely, butyrate-producing gram-positive bacteria related to Eubacterium rectale represented 50% of all 16S rRNA sequences at pH 5.5, but were not detected at pH 6.7. Inhibition of the growth of a major group of gram-negative bacteria at mildly acidic pH apparently creates niches that can be exploited by more low pH-tolerant microorganisms.
Sylvia H Duncan; Petra Louis; John M Thomson; Harry J Flint
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2009-04-21
Journal Detail:
Title:  Environmental microbiology     Volume:  11     ISSN:  1462-2920     ISO Abbreviation:  Environ. Microbiol.     Publication Date:  2009 Aug 
Date Detail:
Created Date:  2009-08-19     Completed Date:  2009-09-30     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  100883692     Medline TA:  Environ Microbiol     Country:  England    
Other Details:
Languages:  eng     Pagination:  2112-22     Citation Subset:  IM    
Microbial Ecology Group, Rowett Institute of Nutrition and Health, University of Aberdeen, Bucksburn, Aberdeen, UK.
Data Bank Information
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MeSH Terms
Base Sequence
Colon / metabolism,  microbiology*
Dietary Carbohydrates / metabolism
Fatty Acids, Volatile / metabolism
Gram-Negative Bacteria / classification,  growth & development*,  isolation & purification,  metabolism
Gram-Positive Bacteria / classification,  growth & development*,  isolation & purification,  metabolism
Hydrogen-Ion Concentration
Molecular Sequence Data
Starch / metabolism
Reg. No./Substance:
0/Dietary Carbohydrates; 0/Fatty Acids, Volatile; 9005-25-8/Starch

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