TABLE 2.

Analysis of metabolites in spent culture medium of D. alaskensis G20 wild type and CycA mutant I2^a

Medium and strain	Concn of substrate or accumulated metabolite remainingb										Protein yield (mg/liter)	Recovery (%)		Initial electron donor/acceptor concn (mM)i
	Pyruvate	Malate	Succinate	Lactate	Fumarate	Formate	Acetate	CO	H2e	H2Sf		Carbong	Reductanth
Lactate-sulfate
G20	NDc	0.2	0.7	27.4	ND	ND	24.1	NQd	0.6	13.7	102.1	102	112	51.9/30.0
I2	ND	ND	ND	32.0	ND	1.6	20.3	ND	1.0	8.8	95.3	101	101	52.0/30.0
Pyruvate-sulfate
G20	34.5	0.3	0.4	ND	ND	1.9	16.4	NQ	0.4	4	85.5	95	103	54.5/15.0
I2	47.6	ND	ND	ND	ND	0.6	5.8	ND	0.9	ND	12.0	100	99	53.4/15.0
Pyruvate
G20	41.0	ND	0.2	ND	0.1	3.2	7.3	ND	0.7	ND	31.3	102	102	48.7
I2	40.4	ND	ND	ND	ND	0.7	7.6	ND	0.9	ND	32.4	99	95	48.0

^aDuplicate 200-ml lactate-sulfate and pyruvate-sulfate cultures were harvested when their growth reached an OD₆₀₀ of ∼0.5, with the exception of I2 on pyruvate-sulfate, which was harvested at an OD₆₀₀ of 0.17. Cells fermenting pyruvate were harvested at an OD₆₀₀ of ∼0.2.

^bThe soluble metabolite concentrations in the filtrates of harvested cultures. Typically, from the inoculum, there was measurable carryover of acetate to the experimental cultures. This carryover amount was subtracted from the concentration reported in the table. Data are in millimolar unless indicated otherwise and are averages of measurements from duplicate cultures.

^cND, not detected.

^dNQ, detected but not quantified. H₂ interfered with the precise measurement of CO with the gas chromatograph.

^eThe H₂ was collected, and the amounts (mmol) produced in a 200-ml culture were calculated by use of the ideal gas law.

^fNo H₂S was detected in the collected gaseous end products, and dissolved H₂S was quantified (34). The 0.5 mM sulfide added at the time of inoculation, to reduce the medium and to provide a sulfur source for fermenting cultures, was subtracted from the sulfide concentration measured at harvest. The lower limit of detection in this experiment was 0.5 mM.

^gThe carbon recovered in culture filtrates was the ratio of the concentration of carbon present in measured end products and the remaining unused substrate to the initial concentration of carbon provided as the electron donor. For the purpose of this calculation, it was assumed that as a primary end product of organic acid oxidation, the CO₂ concentration was essentially equal to that of the acetate generated during growth minus the concentration of any other C₁ or C₄ end products, such as formate, fumarate, and succinate, which were identified and quantified by HPLC. The amount of carbon present in the biomass produced was not taken into account in these calculations.

^hReductant recovery was the ratio of the number of mole equivalents of electrons in the measured end products as well as the electrons remaining in unused substrate to the total number of moles of electrons available for consumption in the substrate added.

ⁱMeasured concentrations of electrons and the carbon donor determined by HPLC, corrected for inoculum carryover, and calculated concentrations of sulfate in the growth media for G20 and I2 at the initiation of growth.