Enrichment of syngas-converting mixed microbial consortia for ethanol production and thermodynamics-based design of enrichment strategies

Table 2 Biochemical reactions, ATP yield and average stoichiometric number used in the thermodynamic potential factor calculation

Stoichiometry of biochemical reactions	ATP yield (mol per reaction)	χ	Refs.
H₂/CO₂ conversion into acetate/ethanol
4 H₂ + 2 CO₂ → CH₃COO⁻ + H⁺ + 2 H₂O	0.3	2	[40]
6 H₂ + 2 CO₂ → CH₃CH₂OH + 3 H₂O	− 0.1/0.3^a	3	[40]
CO conversion into acetate/ethanol
4 CO + 2 H₂O → CH₃COO⁻ + H⁺ + 2 CO₂	1.5	4	[40]
6 CO + 3 H₂O → CH₃CH₂OH + 4 CO₂	1.7	6	[40]
VFA reduction to corresponding alcohols
CH₃COO⁻ + H⁺ + 2 H₂ → CH₃CH₂OH + H₂O	0.33	4	[42]
CH₃(CH₂)₂COO⁻ + H⁺ + 2 H₂ → CH₃(CH₂)₂CH₂OH + H₂O	0.33	4	[42]
CH₃COO⁻ + H⁺ + 2 CO + H₂O → CH₃CH₂OH + 2 CO₂	0.66	5
CH₃(CH₂)₂COO⁻ + H⁺ + 2 CO + H₂O → CH₃(CH₂)₂CH₂OH + 2 CO₂	0.66	5
Chain elongation
5 CH₃CH₂OH + 3 CH₃COO⁻ → 4 CH₃(CH₂)₂COO⁻ + H⁺ + 3 H₂O + 2 H₂	1	1	[41]

^aBertsch and Müller [40] predicted an ATP yield of − 0.1; however, the possibility of a positive ATP yield was also evaluated

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