Protein degradation by human intestinal bacteria.
Analysis of human gut contents showed that substantial quantities of soluble protein, ammonia and branched chain volatile fatty acids occurred throughout the large intestine [0.1-24.4 g (kg contents)-1, 7.7-66.0 mmol (kg contents)-1 and 1.5-11.1 mmol (kg contents)-1 respectively]. The presence of these metabolites suggested that substantial proteolysis was occurring. In vitro studies showed that casein and bovine serum albumin were partly degraded in slurries of human faeces over a 96 h incubation period, to produce TCA-soluble peptides, ammonia and volatile fatty acids. Proteolytic activity detected in the stools of five individuals ranged from 3.5 to 19.8 mg azocasein hydrolysed h-1 (g faecal material)-1. Washed cell and washed particulate faecal fractions accounted for 24-67% of total activity. The predominant proteolytic bacteria in the faecal samples examined were identified as Bacteroides spp. [1.0 X 10(11)-1.3 X 10(12) (g dry wt faeces)-1] and Propionibacterium spp. [1.2 X 10(8)-1.0 X 10(10) (g dry wt faeces)-1]. Other proteolytic bacteria which occurred in lesser numbers were identified as belonging to the genera Streptococcus, Clostridium, Bacillus and Staphylococcus. These results demonstrate that the gut microflora could potentially play a major role in proteolysis in the human colon.
D001407:Bacillus / Q000378:metabolism; D001421:Bacteria, Anaerobic / Q000378:metabolism; D001439:Bacteroides / Q000378:metabolism; D002364:Caseins / Q000378:metabolism; D003013:Clostridium / Q000378:metabolism; D005232:Fatty Acids, Volatile / Q000378:metabolism; D005243:Feces / Q000382:microbiology*; D006801:Humans; D007420:Intestine, Large / Q000378:metabolism; D007421:Intestine, Small / Q000378:metabolism; D010447:Peptide Hydrolases / Q000096:biosynthesis; D011424:Propionibacterium / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D012709:Serum Albumin / Q000378:metabolism; D013210:Staphylococcus / Q000378:metabolism; D013291:Streptococcus / Q000378:metabolism
D002364:Caseins; D005232:Fatty Acids, Volatile; D011506:Proteins; D012709:Serum Albumin; D010447:Peptide Hydrolases