Constancy of glucose and starch fermentations by two different human faecal microbial communities.

The fermentation of glucose and corn starch by faecal suspensions from two subjects was examined over a three and a half year period. The substrate specificity and products of the faecal fermentations of each subject were relatively stable during this period and were significantly different between subjects. The major soluble end products of fermentation of glucose or starch were acetate, propionate, and butyrate. Hydrogen temporarily accumulated and was subsequently used in fermentations by both subjects. Hydrogen was used without methane production in fermentations of subject 1, but was used for methane formation in fermentations of subject 2. Although the rates of glucose fermentation were similar between both subjects; subject 1 produced a significantly greater molar ratio of propionate than did subject 2. The rate of fermentation of starch by faecal suspensions from subject 1 was faster than that of subject 2. The molar ratio of butyrate was greater for starch fermentations by subject 2, while the molar ratio of propionate was greater with subject 1. Significant differences were found between subjects in molar ratios and concentration of acetate and propionate and concentrations of butyrate in faeces.