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/conditionsAmino acids (end of fermentation)End products (mmol/L)Carbon balance (%)
EthanolAcetateBCFABCOHH2H2SCH4

YEND12.1 ± 0.15.2 ± 0.10.4 ± 0.12<0.137.1 ± 0.2NDNDND
YE + S2O3ND2.5 ± 0.28.9 ± 0.30.9 ± 0.120.1 ± 0.03<0.10.3 ± 0.1NDND
YE + M39ND1.0 ± 0.18.7 ± 0.20.9 ± 0.22<0.13<0.1ND2.2 ± 0.1ND

Ala19.2 ± 1.51.2 ± 0.13.4 ± 0.3<1.0<0.110.9 ± 0.2NDNDND
Ala + S2O30.0 ± 0.05.5 ± 0.625.4 ± 0.8<1.0<0.11.3 ± 0.211.5 ± 0.8ND 97.54
Ala + M396.1 ± 1.61.4 ± 0.121.4 ± 2.8<1.0<0.1<0.1ND8.0 ± 0.194.24

Cys19.3 ± 0.01.2 ± 0.13.4 ± 0.1<1.0<0.16.3 ± 0.5NDNDND
Cys + S2O30.2 ± 0.13.0 ± 1.124.2 ± 1.6<1.0<0.11.6 ± 0.112.9 ± 0.4ND79.84
Cys + M390.0 ± 0.01.5 ± 0.125.6 ± 1.7<1.0<0.1<0.1ND8.6 ± 0.487.04

Ile16.2 ± 0.41.4 ± 0.33.0 ± 0.53.8 ± 0.2<0.111.1 ± 0.9NDNDND
Ile + S2O30.0 ± 0.02.9 ± 1.28.1 ± 1.115.9 ± 0.74.4 ± 0.30.2 ± 0.012.5 ± 0.6 ND100.0
Ile + M390.0 ± 0.01.4 ± 0.38.4 ± 1.415.6 ± 1.60.2 ± 0.00.0 ± 0.0ND11.7 ± 1.377.5

Leu 18.5 ± 0.44.9 ± 0.54.2 ± 0.32.0 ± 0.1<0.18.9 ± 0.3NDNDND
Leu + S2O30.0 ± 0.02.9 ± 1.08.1 ± 0.49.7 ± 2.13.5 ± 0.30.6 ± 0.313.5 ± 0.7ND64.5
Leu + M394.0 ± 0.41.3 ± 0.24.3 ± 0.711.7 ± 0.40.4 ± 0.1<0.1ND9.9 ± 0.373.1

Lys20.0 ± 0.01.1 ± 0.12.6 ± 0.1<1.0<0.15.8 ± 0.1NDNDND
Lys + S2O315.9 ± 2.23.7 ± 0.49.9 ± 0.5<1.0<0.10.1 ± 0.02.2 ± 0.4NDND5
Lys + M398.5 ± 1.21.6 ± 0.219.5 ± 6.2<1.0<0.1<0.1ND5.5 ± 0.3ND5

Met19.5 ± 0.53.0 ± 0.94.0 ± 0.2<1.0<0.18.2 ± 0.4NDNDND
Met + S2O33.6 ± 0.53.0 ± 0.36.1 ± 0.3<1.0<0.10.7 ± 0.112.4 ± 0.9NDND
Met + M390.4 ± 0.11.8 ± 0.29.7 ± 0.7<1.0<0.1<0.1ND12.2 ± 0.6ND

Phe20.4 ± 0.6 1.1 ± 0.12.6 ± 0.1<1.0<0.18.0 ± 0.1NDNDND
Phe + S2O38.3 ± 1.02.8 ± 0.36.3 ± 0.4<1.0<0.11.4 ± 0.17.4 ± 0.6NDND
Phe + M390.1 ± 0.0 1.5 ± 0.210.4 ± 1.1<1.0<0.1<0.1ND11.7 ± 0.4ND

Ser4.0 ± 0.55.7 ± 0.515.7 ± 0.6<1.0<0.19.7 ± 0.5NDND87.54
Ser + S2O30.0 ± 0.03.3 ± 1.126.8 ± 1.4<1.0<0.10.1 ± 0.112.5 ± 1.2ND93.54
Ser + M390.0 ± 0.01.5 ± 0.327.5 ± 2.0<1.0<0.1<0.1ND8.8 ± 0.296.54

Thr19.0 ± 1.31.1 ± 0.12.6 ± 0.1<1.0<0.18.0 ± 0.8NDNDND
Thr + S2O314.5 ± 2.53.0 ± 0.425.4 ± 2.1<1.0<0.10.1 ± 0.011.5 ± 1.0NDND6
Thr + M391.5 ± 0.20.8 ± 0.131.2 ± 1.8<1.0<0.1<0.1ND6.9 ± 0.5ND6

Tyr19.3 ± 0.51.1 ± 0.12.6 ± 0.1<1.0<0.16.3 ± 0.5NDNDND
Tyr + S2O36.8 ± 1.33.4 ± 0.17.7 ± 0.3<1.0<0.10.9 ± 0.29.5 ± 0.3NDND
Tyr + M391.2 ± 0.21.4 ± 0.110.0 ± 1.1<1.0<0.1<0.1ND7.1 ± 2.0ND

Val17.4 ± 1.01.1 ± 0.12.6 ± 0.13.3 ± 0.1<0.19.5 ± 0.1NDNDND
Val + S2O30.0 ± 0.03.2 ± 1.17.6 ± 0.619.2 ± 1.01.8 ± 0.50.6 ± 0.212.4 ± 0.5ND103.5
Val + M393.3 ± 1.71.4 ± 0.06.4 ± 1.612.3 ± 2.4<0.1<0.1ND8.9 ± 2.071.8

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).