Table 1.
Effect of iron on the microbial production of SCFAs, and metabolites associated with proteolytic and saccharolytic activity.
| SCFA (saccharolytic mainly) | Proteolytic activity associated | Saccharolytic activity associated | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Acetate (mmol) | Butyrate (mmol) | Propionate (mmol) | Valerate (mmol) | Isovalerate (mmol) | Isobutyrate (mmol) | Ammonia (mmol) | Lactate (a.u.) | Succinate (a.u.) | Formate (mmol/L) | Ethanol (mmol/L) | ||
| Single conditions | lowFe | 66.8 (66.0-67.6) |
40.4 (37.2-43.6) |
14.1 (11.5-16.7) |
0.0 a (0.0-0.0)* |
0.1 (0.0-0.3)* |
0.0 (0.0-0.0)* |
30.5 (29.1-31.9) |
100.0 a (66.4-133.6) |
100.0 a (8.6-191.4) |
2.1 a (2.1-2.1) |
2.1 a (2.0-2.2) |
| 50FeS | 84.2 (73.6–94.4) |
46.1 (43.1-49.0) |
17.7 (14.8-20.5) |
0.9 ab (0.7-1.1) |
1.5 (1.3-1.6) |
0.6 (0.6-0.7) |
52.1 (48.7-55.5) |
7.3 b (7.2-7.4) |
202.3 ac (49.4-355.3) |
0.4 b (0.4-0.5) |
0.4 b (0.3–0.6) |
|
| 250FeS | 83.8 (79.7-87.9) |
46.0 (43.9-48.1) |
26.1 (21.1-31.2) |
1.5 b (1.2-1.8) |
1.7 (1.5-2.0) |
0.7 (0.6-0.7) |
57.5 (56.2-58.8) |
6.1 b (5.5-6.6) |
4.7 a (2.3–7.1) |
0.4 b (0.4-0.4) |
0.2 b (0.1-0.2) |
|
| 50FeC | 76.2 (71.6-80.8) |
53.0 (51.2-54.8) |
16.0 (15.9-16.1) |
0.2 a (0.1-0.3) |
0.6 (0.5-0.7) |
0.1 (0.1-0.1) |
50.3 (48.0-52.7) |
5.9 b (4.4-7.4) |
632.8 b (627.4-638.1) |
0.4 b (0.4-0.5) |
1.6 a (1.3-1.8) |
|
| 250FeC | 83.0 (74.9-91.1) |
46.4 (43.8-49.0) |
30.3 (28.4-32.3) |
0.9 ab (0.5-1.3) |
0.7 (0.1-1.3) |
0.3 (0.0-0.5)* |
47.7 (36.6-58.7) |
6.3 b (6.3-6.3) |
13.3 a (6.3-20.3) |
|||
| FeH | 80.6 (76.6-84.6) |
37.4 (34.5-40.3) |
28.0 (23.1-33.0) |
0.1 a (0.1-0.2) |
0.3 (0.1-0.5) |
0.1 (0.0-0.1)* |
40.7 (35.7-45.7) |
7.0 b (6.2-7.7) |
527.9 bc (524.2-531.6) |
0.5 b (0.5-0.5) |
1.6 a (1.4-1.8) |
|
| Iron level (grouped) | lowFe | 66.8 (66.0-67.6) |
40.4 ab (37.2-43.6) |
14.1 a (11.5-16.7) |
0.0 (0.0-0.0)* |
0.1 (0.0-0.3)* |
0.0 (0.0-0.0)* |
30.5 a (29.1-31.9) |
100.0 a (66.4-133.6) |
100.0 ab (8.6-191.4) |
||
| MediumFe | 80.2 (71.6-94.9) |
49.5 a (43.1-54.8) |
16.8 ab (14.8-20.5) |
0.6 (0.1-1.1) |
1.0 (0.5-1.6) |
0.4 (0.1-0.7) |
51.2 b (48.0-55.5) |
6.6 b (4.4-7.4) |
417.5 a (49.4-638.1) |
|||
| HighFe | 83.4 (74.9-91.1) |
46.2 ab (43.8-49.0) |
28.2 c (21.1-32.3) |
1.2 (0.5-1.8) |
1.2 (0.1-2.0) |
0.5 (0.0-0.7)* |
52.6 b (36.6-58.8) |
6.2 b (5.5-6.6) |
9.0 b (2.3-20.3) |
|||
| FeH | 80.6 (76.6-84.6) |
37.4 b (34.5-40.3) |
28.0 abc (23.1-33.0) |
0.1 (0.1-0.2) |
0.3 (0.1-0.5) |
0.1 (0.0-0.1)* |
40.7 ab (35.7-45.7) |
7.0 b (6.2-7.7) |
527.9 a (524.2-531.6) |
|||
| Iron source (grouped) | LowFe | 66.8 (66.0-67.6) |
40.4 ab (37.2-43.6) |
14.1 (11.5-16.7) |
0.0 a (0.0-0.0)* |
0.1 a (0.0-0.3)* |
0.0 a (0.0-0.0)* |
30.5 a (29.1-31.9) |
100.0 a (66.4-133.6) |
100.0 (8.6-191.4) |
||
| FeS | 84.0 (73.6-94.4) |
46.0 ab (43.1-49.0) |
21.9 (14.8-31.2) |
1.2 b (0.7-1.8) |
1.6 b (1.3-2.0) |
0.6 b (0.6-0.7) |
54.8 b (48.7-58.8) |
6.7 b (5.5-7.4) |
103.5 (2.3-355.3) |
|||
| FeC | 79.6 (71.6-91.1) |
49.7 a (43.8-54.8) |
23.2 (15.9-32.3) |
0.5 ab (0.1-1.3) |
0.6 a (0.1-1.3) |
0.2 a (0.0-0.6)* |
49.0 ab (36.6-58.7) |
6.1 b (4.4-7.4) |
323.0 (6.3-638.1) |
|||
| FeH | 80.6 (76.6-84.6) |
37.4 b (34.5-40.3) |
28.0 (23.1-33.0) |
0.1 ab (0.1-0.2) |
0.3 a (0.1-0.5) |
0.1 a (0.0-0.1)* |
40.7 ab (35.7-45.7) |
7.0 b (6.2-7.7) |
527.9 (524.2-531.6) |
|||
Cumulative levels in the lumen and dialysate at 72 h (mean+range) of the main SCFAs acetate, butyrate and propionate are given for the single conditions, the grouped mediumFe and highFe conditions, and the grouped FeS and FeC conditions. Cumulative levels at 72 h (mean+range) of valerate, the BCFAs isobutyrate and isovalerate, and ammonia (proteolytic activity associated metabolites) are displayed the same way. The saccharolytic activity associated metabolites lactate, succinate, formate and ethanol were measured by organic acid analysis and/or 1H-NMR spectroscopy in the dialysate at 72 h. Lactate and succinate levels (mean+range) are shown relative to the lowFe control which was set at 100%; the average concentrations of lactate and formate in the lowFe condition were 3.3 mmol/L and 0.29 mmol/L respectively, as quantified by 1H-NMR spectroscopy. Formate and ethanol levels (mean+range) as determined by 1H-NMR spectroscopy are not shown for grouped conditions because the 250FeC condition was not analyzed by 1H-NMR spectroscopy. Means of the same metabolite, and within its horizontal category, without a common letter differ significantly (p < 0.05; Tukey's multiple comparison post-hoc test). N = 2 for the single conditions, and n = 4 for the grouped conditions mediumFe, highFe, FeS, and FeC.
Value of 0 was assigned when a metabolite was below the detection limit.