TABLE A4. Mass balance and energetics of methanogenic syntrophic degradation of toluene under
experimental batch enrichment conditions1.
Biochemical reaction
Energy
Organism and process
Potential (V)
07
Eq.
GROWTH YIELD-INDEPENDENT REACTIONS
Eh
Redox active components
7
Eh
G rxn (kJ)
07
G
7
G
Assimilatory reactions
-
-
-
Toluene assimilation per C-mole cells
1.1
(4/36)C7H8(36e ) + 0.22CO2(0e ) → CellC(4e )
Acetate assimilation per C-mole cells
1.2
(4/8)C2H3O2-(8e-) → CellC(4e-)
0.111C7H8 + 0.22CO2 → CellC
27
31
27
38
-21
40
148
-76
95
-3
-36
-39
-33
-9
0.060C7H8 + 0.12CO2 → 0.54CellC
15
17
(1-0.06)(C7H8 + 12H+ → 3C2H3O2- +CO2 + 6H2 )
0.94C7H8 + 11.28H+ → 2.82C2H3O2- + 0.94CO2
+ 5.64H2
C7H8 + 11.28H+ → 2.82C2H3O2- + 0.82CO2 +
5.64H2 + 0.54CellC
139
-71
154
-54
0.5C2H3O2- →
CellC
CO2 assimilation per C-mole cells
-
e acceptor: CO2 reduction to cell C
-
-
e donor: H2 oxidation to protons
1.3.2
Assimilatory reaction per C-mole cells
1.3.3
-
-
4e + CO2(0e ) →
1.3.1
-
CellC(4e )
+
-
H2(2e ) → 2H (0e )
-
-
+
2H2(2e ) + CO2(0e ) →
-
-0.36
-0.3703
-0.4141
-0.2661
-
4H (0e ) + CellC(4e )
4H+ + CellC
2H2 + CO2 →
Dissimilatory reactions
Toluene dissimilation
e- donor: toluene oxidation to acetate & CO2
-
2.1.1
-
-
-
C7H8(36e-) → 3C2H3O2 (8e ) + CO2(0e ) + 12e
-
+
-
-
-
e acceptor: proton reduction to H2
2.1.2
2e + 2H (0e ) → H2(2e )
Dissimilatory reaction per mole toluene
2.1.3
C7H8 + (12/2)2H+ → 3C2H3O2 + CO2 + (12/2)H2
-0.2862
-0.3314
-0.4141
-0.2661
C7H8 + 12H+ → 3C2H3O2 + CO2 + 6H2
Acetate dissimilation: reverse acetyl CoA
e- donor: acetate oxidation to CO2
-
2.2.1
e acceptor: proton reduction to H2
2.2.2
Dissimilatory reaction per mole acetate
2.2.3
-
-
2CO2(0e-) + 8e-
C2H3O2 (8e ) →
-
+
-
2e + 2H (0e ) → H2(2e-)
+
C2H3O2 (8e ) + (8/2)2H (0e ) → 2CO2(0e ) +
(8/2)H2(2e )
+
C2H3O2 + 8H → 2CO2 + 4H2
-0.2910
-0.2706
-0.4141
-0.2661
Acetate dissimilation: intramolecular fermentation
Acetate to CO2 and methane per mole acetate 2.3
-
-
C2H3O2 (8e ) →
CO2(0e-) + CH4(8e-)
Hydrogen dissimilation
e- donor: H2 oxidation o protons
-
H2(2e-) → 2H+(0e-)
2.4.1
e acceptor: CO2 reduction to methane
2.4.2
dissimilatory reaction per mole H2
2.4.3
-0.4141
-0.2661
8e + CO2(0e-) →CH4(8e-)
-0.2447
H2(2e ) + (2/8)CO2(0e-) → 2H+(0e-) + (2/8)CH4
(8e-)
H2 + 0.25CO2 → 2H+ + 0.25CH4
-0.2203
-
GROWTH YIELD-DEPENDENT REACTIONS
Syntroph 1
Toluene consuming, acetate, CO2, & H2 producer
Growth reaction per mole toluene
Assimilatory reaction per 0.54 C-mole cells
Dissimilatory reaction per 0.54 C-mole cells
Growth reaction per 0.54 C-mole cells
3.1
3.1.1
3.1.2
3.1.3
C7H8 + ?H+ → ?C2H3O2- + ?CO2 + 0.54CellC
(0.54)(0.111C7H8 + 0.22CO2 → CellC)
Biochemical reaction
Energy
Organism and process
Potential (V)
07
Eq.
Redox active components
Eh
7
Eh
G rxn (kJ)
07
7
G
G
Syntroph 2
Acetate consuming, CO2 & H2 producer
Growth rxn per 1.41 mole acetate/mole toluene
Assimilatory reaction per 0.04 C-mole cells
3.2
3.2.1
C2H3O2- + ?H+ → ?CO2 + ?H2 + 0.04CellC
0.04 (0.5C2H3O2- →
0.02C2H3O2- g
Dissimilatory reaction per 0.04 C-mole cells
Growth reaction per 0.04 C-mole cells
3.2.2
3.2.3
CellC)
1
2
132
-5
133
-3
1
2
-50
-54
-49
-52
-1
1
11.12H2 + 2.78CO2 g 22.24H+ + 2.78CH4
11.20H2 + 2.82CO2 g 22.40H+ + 2.78CH4 +
0.04CellC
-364
-99
-364
-97
C7H8 g 2.17CO2 + 4.17CH4 + 0.66CellC
-126
-207
0.04CellC
(1.41-0.02)(C2H3O2- + 8H+ →
2CO2 + 4H2)
1.39C2H3O2- + 11.12H+ → 2.78CO2 + 5.56H2
1.41C2H3O2- + 11.12H+ → 2.78CO2 + 5.56H2 +
0.04CellC
Syntroph 3
Acetate consuming, CO2 and methane producer
Growth rxn per 1.41 mole acetate/mole toluene
Assimilatory reaction per 0.04 C-mole cells
3.3
3.3.1
C2H3O2 → ?CO2 + ?CH4 + 0.04CellC
0.04(0.5C2H3O2 →
0.02C2H3O2 →
Dissimilatory reaction per 0.04 C-mole cells
Growth reaction per 0.04 C-mole cells
3.3.2
3.3.3
CellC)
0.04CellC
(1.41-0.02)(C2H3O2 →
CO2 + CH4)
1.39C2H3O2 →1.39CO2 + 1.39CH4
1.41C2H3O2 → 1.39CO2 + 1.39CH4 +
0.04CellC
Syntroph 4
H2 and CO2 consuming, methane producer
Growth rxn per 11.20 mole H2/mole toluene
Assimilatory reaction per 0.04 C-mole cells
3.4
3.4.1
(5.64+5.56)H2 + ?CO2 →
0.04(2H2 + CO2 →
0.08H2 + 0.04CO2 →
Dissimilatory reaction per 0.04 C-mole cells
Growth reaction per 0.04 C-mole cells
3.4.2
3.4.3
?CH4 + 0.04CellC
4H+ + CellC)
0.16H+ + 0.04CellC
(11.20-0.08)(H2 + 0.25CO2 g2H+ + 0.25CH4)
Consortium
Toluene consuming, CO2 and methane producer
Growth reaction per mole toluene
1
3.5 2
From Edwards and Grbic-Galic (1994) and Ficker et al. (1999). An anaerobic enrichment consortium of toluene degraders and methanogens consisted
of 4 major types: 1) an organism oxidizing toluene and releasing acetate and/or one or more other oxidative or fermentation pathway intermediates (we
chose toluene oxidation to acetate coupled to H+ reduction to H2); 2) an organism oxidizing a toluene degradation pathway intermediate, and releasing
acetate and/or H 2 (we chose an organism capable of using the reversible acetyl CoA pathway, with acetate oxidation to CO2 and H + reduction to H2, or
the reverse depending on metabolite concentrations (Zinder, 1994); 3) an acetate fermenting methanogen, producing CO2 and methane; and 4) an H2using methanogen reducing CO2 to methane. The consortium growth yield per mole toluene was 17.0 g (17.0*0.46/12 = 0.65 C-mole) cells. For
illustration purposes we partition the yield as follows: Syntroph 1, 14.0 g (0.54 C-mole) cells; Syntrophs 2, 3, and 4, 1.0 g (0.04 C-mole) cells each.
Concentration conditions: 0.1 mM toluene; 0.70 mM acetate; 0.20% atm CO2 gas; and, hypothesized by us, 10-5 atm H2 and 10-4 atm CH4.
2
Eq 3.5 = Eq 3.1.3 + Eq 3.2.3 + Eq 3.3.3 + Eq 3.4.3.