Improvement of L-phenylalanine production from glycerol by recombinant Escherichia coli strains: The role of extra copies of glpK, glpX, and tktA genes

Table 2 Comparison of the results from the fed-batch fermentations with FUS4/pF81 and its derivatives

Strain	Growth rate	Maximal carbon recovery Y C _Phe /C _Gly	Maximal space-time-yield	Maximal concentration L-Phe	Lactate conc.	Acetate conc.
	(μ [h⁻¹])	[mM] ([%])	[g l⁻¹ h⁻¹] ([%])	[g l⁻¹] ([%])	[mM]	[mM]
FUS4/pF81	0.27 ± 0.01	0.18 ± 0.02 (100)	0.21 ± 0.02 (100)	7.9 ± 0.2 (100)	30.7 ± 10.5	9.5 ± 5.5
FUS4/pF81 (20% O₂)	0.26 ± 0.01	0.26 ± 0.03 (144.4)	0.26 ± 0.01 (123,8)	9.4 ± 0.7 (119,0)	n.d.*	n.d.
FUS4/pF81 (Glucose)	0.49 ± 0.01	0.19 ± 0.02 (105.6)	0.13 ± 0.01 (61.9)	5.5 ± 1.3 (69.6)	15.4 ± 4.7	3.0 ± 0.7
FUS4/pF81 (crude glycerol, 20% O₂)	0.32 ± 0.01	0.23 ± 0.05 (127.8)	0.22 ± 0.05 (104.8)	10.0 ± 0.9 (126.6)	46.8 ± 1.5	24.9 ± 6.8
FUS4.5/pF81	0.28 ± 0.02	0.21 ± 0.04 (116.7)	0.23 ± 0.01 (109.5)	9.7 ± 0.8 (124.0)	69.1 ± 9.5	21.9 ± 3.7
FUS4.6/pF81	0.29 ± 0.03	0.20 ± 0.01 (111.1)	0.25 ± 0.02 (119.0)	7.3 ± 0.5 (92.4)	21.1 ± 1.4	3.2 ± 0.4
FUS4.7/pF81	0.24 ± 0.01	0.26 ± 0.06 (144.4)	0.37 ± 0.01 (180.5)	10.1 ± 0.2 (127.8)	31.3 ± 5.0	7.9 ± 3.8

n.d. not detectable, *lactate was not detectable as long as the glycerol concentration stayed below 5 g/l.
All fed-batch fermentations were conducted two times independently in MM in a 3.6 l bioreactor (as described in Materials and methods). If not stated otherwise, (in brackets) pure glycerol was used as carbon source and oxygen saturation was at 60%. The values represent the mean value and the standard deviation.

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