TABLE 2.

Effect of pH and peptide input on final metabolite concentrations for fecal microbial communities in continuous culture

Metabolite	Concn (mM)a upon incubation at:
	pH 6.5b		pH 5.5c		pH 6.5c (shifted from pH 5.5)		Meand
	Donor 1	Donor 2	Donor 1	Donor 2	Donor 1	Donor 2	pH 6.5	pH 5.5
Medium + 0.6% peptide
Formate	0.5	0.5	0.3	0.1	0.3	0.3	0.4	0.2
Acetate	32.3	28.2	11.4	14.0	28.4	32.3	30.3	12.7
Propionate	20.1	18.3	10.1	5.1	23.2	20.6	20.6	7.6
Butyrate	4.3	5.8	26.3	23.5	6.3	4.9	5.3	24.9
Valerate	2.4	0.2	1.2	0.5	2.8	2.5	2.0	0.9
Succinate	1.3	1.9	0	0	0	0	0.8	0
dl-Lactate	1.4	0.3	0	0	0	0.4	0.5	0
Ammonia	7.7	4.3	2.3	1.5	0.9	1.0	3.5	1.9
Medium + 0.1% peptide
Formate	7.8	0.3	0.3	5.6	6.4	0.6	3.8	3.0
Acetate	26.4	33.3	42.2	34.1	45.3	32.1	34.3	38.2
Propionate	12.0	6.1	4.2	0.9	6.6	5.6	7.6	2.6
Butyrate	7.3	5.2	16.1	11.4	5.3	12.7	7.6	13.8
Valerate	1.2	0.1	0.5	0.5	0.5	0.9	0.7	0.5
Succinate	0	4.7	0	3.6	1.7	2.5	2.2	1.8
dl-Lactate	3.7	2.7	0	1.2	1.9	0.6	2.2	0.6
Ammonia	0.07	0.09	0.2	0.03	0.08	0.02	0.07	0.12

^aMeans of three determinations are shown; typical errors can be seen from Fig. 1 and 2.

^bFrom the experiment shown in Fig. 1 (but including data for donor 1). Data refer to the final (192-h) time point.

^cFrom the experiment shown in Fig. 2 (but including data for the low-peptide condition). Data refer to the final time point at the relevant pH (donor 1, 144 h, pH 5.5, and 360 h, pH 6.5; donor 2, 216 h, pH 5.5, and 458 h, pH 6.5).

^dOverall means of preceding four values at pH 6.5, two at 5.5; the statistical analysis (analysis of variance) is described in the text.