Redox dependent metabolic shift in Clostridium autoethanogenum by extracellular electron supply

Table 3 Carbon balance accounting for metabolite production from fructose only (top) and Flux optimization of a C. autoethanogenum metabolic network using the experimental rates as constraints in CellNetAnalyzer (bottom)

Condition	Fructose consumed	Metabolites produced (mmol/L)					C-balance (%)
Condition	Fructose consumed	Acetate	Lactate	Ethanol	2,3-BDO	CO₂ ^a	C-balance (%)
Control	26.94	46.43	0.28	17.63	0.73	65.52	122.12
BES	27.24	42.36	0.34	21.57	0.78	65.49	120.83
BES + [Co(sep)]³⁺	27.24	48.22	0.34	13.83	0.48	63.01	116.28
BES + [Co(AMMEsar)]³⁺	25.47	40.90	0.31	19.74	0.68	62	122.32
BES + [Co(trans-diammac)]³⁺	25.99	21.11	9.87	19.04	2.21	44.57	104.71

Condition	Minimizing fructose consumption					Maximizing ATP maintenance
Condition	CO₂ out	H₂ out	ATP main	min fructose	YE (%)	CO₂ out	H₂ out	ATP main	YE (%)
Control	3.11	0.0	7.38	3.01	89.2	3.11	0.00	12.62	84.9
BES	3.19	0.0	7.19	2.67	87.3	3.01	0.00	12.09	53.6
BES + [Co(sep)]³⁺	1.85	0.0	6.29	2.23	88.0	3.16	3.10	7.81	0.0
BES + [Co(AMMEsar)]³⁺	2.68	0.0	7.38	2.74	88.0	3.83	2.76	9.96	0.0
BES + [Co(trans-diammac)]³⁺	4.94	0.0	9.02	4.51	88.6	5.02	0.81	12.75	0.0

Surplus carbon is allowed to leave the system as CO₂, surplus redox power leaves as H₂, ATP main(tenance) flux highlights energy surplus. Yeast extract (YE) flux is calculated on the assumed molecular composition and given as a percentage (%) of the total available yeast extract flux (compare M&M). Minimal fructose flux is the minimal rate of fructose uptake required to meet the observed production rates, based on optimal use of the YE. Apart from the YE all fluxes are given in (mmol/g_CDW h). The underlying network can be found in Additional file 1: Table S1
^aCO₂ production assumed from stoichiometric decarboxylation steps needed for production of acetate and ethanol (1 mol/mol) and 2,3-butanediol (2 mol/mol)

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