TABLE 1.

Physiological analysis of chemostat cultures of S. cerevisiae in the presence and absence of high lactate concentrations^a

Physiological parameter (units)	Avg value ± SD
	pH 5		pH 3
	Reference (no acid)	900 mM lactic acid	Reference (no acid)	500 mM lactic acid
Glucose (mmol g−1 h−1)	−6.03 ± 0.10	−11.46 ± 0.31	−6.96 ± 0.39	−10.32 ± 0.37
CO2 (mmol g−1 h−1)	10.40 ± 0.45	17.63 ± 0.85	11.76 ± 0.29	18.02 ± 0.32
Ethanol (mmol g−1 h−1)	9.52 ± 0.16	13.13 ± 0.27	10.99 ± 0.43	17.56 ± 0.74
Glycerol (mmol g−1 h−1)	0.79 ± 0.02	5.06 ± 0.41	0.83 ± 0.04	1.90 ± 0.07
Lactate (mmol g−1 h−1)	0.05 ± 0.01	NDb	0.09 ± 0.01	ND
Acetate (mmol g−1 h−1)	0.02 ± 0.00	0.72 ± 0.09	0.02 ± 0.00	0.10 ± 0.01
Biomass (g liter−1)	2.25 ± 0.02	1.21 ± 0.02	2.03 ± 0.04	1.21 ± 0.04
Biomass yield (g [g glucose]−1)	0.09 ± 0.00	0.05 ± 0.00	0.09 ± 0.00	0.05 ± 0.01
Carbon recovery (%)c	99.4 ± 0.8	93.1 ± 2.5	96.46 ± 3.1	98.52 ± 3.3
Residual glucose (mM)	0.2 ± 0.0	3.0 ± 0.8	0.4 ± 0.1	10.3 ± 1.3

^aPhysiology of anaerobic, glucose-limited, chemostat cultures of S. cerevisiae (dilution rate, 0.10 h⁻¹) grown in the presence and absence of high lactate concentrations at pH 5 and pH 3. Lactate concentrations were chosen such that they resulted in an approximately 50% decrease of the biomass yield relative to that of the reference condition (Fig. 1). Specific rates of glucose consumption and product formation and other parameters are represented as averages ± standard deviations (SD) for three independent cultures for each condition. Due to the high concentrations of lactic acid added to these cultivations, the production or consumption rates of lactic acid could not be determined accurately. For the same reason, lactate was not included in calculations of carbon recovery for these conditions.

^bND, not determined.

^cAcetaldehyde fluxes were not included in the determination of carbon recovery as acetaldehyde measurements were performed only for cultures at pH 5 with lactic acid.