Metabolic engineering of Escherichia coli for the production of butyric acid at high titer and productivity

Table 2 Fermentation characteristics of E. coli strain LW393 and its derivatives

Strain	Relevant property^a	Medium	Sugar	Cell density^b	Butyrate titer (g l⁻¹)	q_P (g g cells⁻¹ h⁻¹)^c	Q_P (g l⁻¹ h⁻¹)^d	Yield (g g⁻¹ sugar)^e
LW393	PTB/BUK	LB	Glucose	11.0 ± 0.03	19.7 ± 0.1	0.21 ± 0.01	0.47 ± 0.01	0.42 ± 0.01
		LB	Xylose	8.2 ± 0.03	25.1 ± 0.4	0.20 ± 0.03	0.36 ± 0.02	0.40 ± 0.01
		Mineral salts	Glucose	10.8 ± 0.20	28.4 ± 0.4	0.25 ± 0.04	0.64 ± 0.04	0.37 ± 0.01
		Mineral salts	Glucose + YE	10.5 ± 0.40	33.1 ± 0.3	0.26 ± 0.09	0.76 ± 0.04	0.35 ± 0.01
		Mineral salts	Xylose	9.4 ± 0.40	27.3 ± 0.8	0.30 ± 0.01	0.60 ± 0.02	0.37 ± 0.01
		Mineral salts	Xylose + YE	10.8 ± 0.17	31.7 ± 0.4	0.36 ± 0.03	0.89 ± 0.07	0.37 ± 0.01
LW483	(-PTB/BUK)	Mineral salts	Glucose	4.7 ± 0.04	14.6 ± 1.0	0.16 ± 0.02	0.20 ± 0.03	0.41 ± 0.01
LW532	LW483, ΔtesB	Mineral salts	Glucose	2.8 ± 0.20	8.8 ± 0.7	0.19 ± 0.03	0.12 ± 0.03	0.41 ± 0.02
LW612	LW532(ptesB)	Mineral salts	Glucose + (IPTG, 10 µM)	4.9 ± 0.10	20.1 ± 0.5	ND	0.30 ± 0.01	0.37 ± 0.01

Cultures were grown in LB or AM1 medium with glucose or xylose ± yeast extract (5 g l⁻¹). All media were supplemented with additional trace elements as presented in “Materials and methods”. Fermentations were at 37 °C and the culture pH was maintained at 7.0 by automatic addition of 2 N KOH. N₂ was sparged through the culture from the beginning (7 ml min⁻¹) to maintain anaerobic condition
All reported values are average of three independent experiments with standard deviation
^a(PTB/BUK), pathway from butyryl-CoA to butyrate utilizes phosphotransbutyrylase and butyrate kinase (Fig. 1). (-PTB/BUK), plasmid p185 encoding ptb and buk was removed from strain LW393. Strain LW612 carries plasmid pLW108 containing E. coli tesB expressed from trc promoter
^bCell density is presented as O. D. 420 nm
^cq_P, specific productivity; unit, g butyrate produced per g dry cell weight per h
^dQ_P, Average volumetric productivity of butyrate over a 24-h period
^eYield, g butyrate (g sugar consumed)⁻¹

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