Amino Acid Metabolism of Thermoanaerobacter Strain AK90: The Role of Electron-Scavenging Systems in End Product Formation
Table 1
End product formation from amino acids by Thermoanaerobacter strain AK90. Initial amino acid concentration was 20 mM in all cases. Experiments were done with and without electron-scavenging systems, either with 40 mM of thiosulfate () or in a coculture with a hydrogenotrophic methanogen (M39). Data represent the average of two replicate experiments ± standard deviation. Experiments without added carbon source only contained 2 g/L of yeast extract (YE). Branched-chain fatty acids (BCFAs) are 3-methylbutyrate from leucine, 2-methylbutyrate from isoleucine, and 2-methylpropionate from valine. Branched-chain alcohols (BCOHs) are 3-methylbutanol from leucine, 2-methylbutanol from isoleucine, and 2-methylpropanol from valine.
Substrate/conditions
Amino acids (end of fermentation)
End products (mmol/L)
Carbon balance (%)
Ethanol
Acetate
BCFA
BCOH
H2
H2S
CH4
YE
ND1
2.1 ± 0.1
5.2 ± 0.1
0.4 ± 0.12
<0.13
7.1 ± 0.2
ND
ND
ND
YE + S2O3
ND
2.5 ± 0.2
8.9 ± 0.3
0.9 ± 0.12
0.1 ± 0.03
<0.1
0.3 ± 0.1
ND
ND
YE + M39
ND
1.0 ± 0.1
8.7 ± 0.2
0.9 ± 0.22
<0.13
<0.1
ND
2.2 ± 0.1
ND
Ala
19.2 ± 1.5
1.2 ± 0.1
3.4 ± 0.3
<1.0
<0.1
10.9 ± 0.2
ND
ND
ND
Ala + S2O3
0.0 ± 0.0
5.5 ± 0.6
25.4 ± 0.8
<1.0
<0.1
1.3 ± 0.2
11.5 ± 0.8
ND
97.54
Ala + M39
6.1 ± 1.6
1.4 ± 0.1
21.4 ± 2.8
<1.0
<0.1
<0.1
ND
8.0 ± 0.1
94.24
Cys
19.3 ± 0.0
1.2 ± 0.1
3.4 ± 0.1
<1.0
<0.1
6.3 ± 0.5
ND
ND
ND
Cys + S2O3
0.2 ± 0.1
3.0 ± 1.1
24.2 ± 1.6
<1.0
<0.1
1.6 ± 0.1
12.9 ± 0.4
ND
79.84
Cys + M39
0.0 ± 0.0
1.5 ± 0.1
25.6 ± 1.7
<1.0
<0.1
<0.1
ND
8.6 ± 0.4
87.04
Ile
16.2 ± 0.4
1.4 ± 0.3
3.0 ± 0.5
3.8 ± 0.2
<0.1
11.1 ± 0.9
ND
ND
ND
Ile + S2O3
0.0 ± 0.0
2.9 ± 1.2
8.1 ± 1.1
15.9 ± 0.7
4.4 ± 0.3
0.2 ± 0.0
12.5 ± 0.6
ND
100.0
Ile + M39
0.0 ± 0.0
1.4 ± 0.3
8.4 ± 1.4
15.6 ± 1.6
0.2 ± 0.0
0.0 ± 0.0
ND
11.7 ± 1.3
77.5
Leu
18.5 ± 0.4
4.9 ± 0.5
4.2 ± 0.3
2.0 ± 0.1
<0.1
8.9 ± 0.3
ND
ND
ND
Leu + S2O3
0.0 ± 0.0
2.9 ± 1.0
8.1 ± 0.4
9.7 ± 2.1
3.5 ± 0.3
0.6 ± 0.3
13.5 ± 0.7
ND
64.5
Leu + M39
4.0 ± 0.4
1.3 ± 0.2
4.3 ± 0.7
11.7 ± 0.4
0.4 ± 0.1
<0.1
ND
9.9 ± 0.3
73.1
Lys
20.0 ± 0.0
1.1 ± 0.1
2.6 ± 0.1
<1.0
<0.1
5.8 ± 0.1
ND
ND
ND
Lys + S2O3
15.9 ± 2.2
3.7 ± 0.4
9.9 ± 0.5
<1.0
<0.1
0.1 ± 0.0
2.2 ± 0.4
ND
ND5
Lys + M39
8.5 ± 1.2
1.6 ± 0.2
19.5 ± 6.2
<1.0
<0.1
<0.1
ND
5.5 ± 0.3
ND5
Met
19.5 ± 0.5
3.0 ± 0.9
4.0 ± 0.2
<1.0
<0.1
8.2 ± 0.4
ND
ND
ND
Met + S2O3
3.6 ± 0.5
3.0 ± 0.3
6.1 ± 0.3
<1.0
<0.1
0.7 ± 0.1
12.4 ± 0.9
ND
ND
Met + M39
0.4 ± 0.1
1.8 ± 0.2
9.7 ± 0.7
<1.0
<0.1
<0.1
ND
12.2 ± 0.6
ND
Phe
20.4 ± 0.6
1.1 ± 0.1
2.6 ± 0.1
<1.0
<0.1
8.0 ± 0.1
ND
ND
ND
Phe + S2O3
8.3 ± 1.0
2.8 ± 0.3
6.3 ± 0.4
<1.0
<0.1
1.4 ± 0.1
7.4 ± 0.6
ND
ND
Phe + M39
0.1 ± 0.0
1.5 ± 0.2
10.4 ± 1.1
<1.0
<0.1
<0.1
ND
11.7 ± 0.4
ND
Ser
4.0 ± 0.5
5.7 ± 0.5
15.7 ± 0.6
<1.0
<0.1
9.7 ± 0.5
ND
ND
87.54
Ser + S2O3
0.0 ± 0.0
3.3 ± 1.1
26.8 ± 1.4
<1.0
<0.1
0.1 ± 0.1
12.5 ± 1.2
ND
93.54
Ser + M39
0.0 ± 0.0
1.5 ± 0.3
27.5 ± 2.0
<1.0
<0.1
<0.1
ND
8.8 ± 0.2
96.54
Thr
19.0 ± 1.3
1.1 ± 0.1
2.6 ± 0.1
<1.0
<0.1
8.0 ± 0.8
ND
ND
ND
Thr + S2O3
14.5 ± 2.5
3.0 ± 0.4
25.4 ± 2.1
<1.0
<0.1
0.1 ± 0.0
11.5 ± 1.0
ND
ND6
Thr + M39
1.5 ± 0.2
0.8 ± 0.1
31.2 ± 1.8
<1.0
<0.1
<0.1
ND
6.9 ± 0.5
ND6
Tyr
19.3 ± 0.5
1.1 ± 0.1
2.6 ± 0.1
<1.0
<0.1
6.3 ± 0.5
ND
ND
ND
Tyr + S2O3
6.8 ± 1.3
3.4 ± 0.1
7.7 ± 0.3
<1.0
<0.1
0.9 ± 0.2
9.5 ± 0.3
ND
ND
Tyr + M39
1.2 ± 0.2
1.4 ± 0.1
10.0 ± 1.1
<1.0
<0.1
<0.1
ND
7.1 ± 2.0
ND
Val
17.4 ± 1.0
1.1 ± 0.1
2.6 ± 0.1
3.3 ± 0.1
<0.1
9.5 ± 0.1
ND
ND
ND
Val + S2O3
0.0 ± 0.0
3.2 ± 1.1
7.6 ± 0.6
19.2 ± 1.0
1.8 ± 0.5
0.6 ± 0.2
12.4 ± 0.5
ND
103.5
Val + M39
3.3 ± 1.7
1.4 ± 0.0
6.4 ± 1.6
12.3 ± 2.4
<0.1
<0.1
ND
8.9 ± 2.0
71.8
ND: not determined. 2Total of 3-methylbutyrate, 2-methylbutyrate, and 2-methylpropionate. 3Total of 3-methylbutanol, 2-methylbutanol, and 2-methylpropanol. 4Assuming that CO2 is produced in equimolar ratio with the production of acetate and ethanol. 5Butyrate was produced (2.2 mM) but not shown in the table for simplicity reasons. 6Degradation pathway unknown and thus not calculated (see results and discussion).
