Enhancement of l-phenylalanine production by engineered Escherichia coli using phased exponential l-tyrosine feeding combined with nitrogen source optimization

Nitrogen source optimization combined with phased exponential l-tyrosine feeding was employed to enhance l-phenylalanine production by a tyrosine-auxotroph strain, Escherichia coli YP1617. The absence of (NH₄)₂SO₄, the use of corn steep powder and yeast extract as composite organic nitrogen source were more suitable for cell growth and l-phenylalanine production. Moreover, the optimal initial l-tyrosine level was 0.3gL^-1 and exponential l-tyrosine feeding slightly improved l-phenylalanine production. Nerveless, l-phenylalanine production was greatly enhanced by a strategy of phased exponential l-tyrosine feeding, where exponential feeding was started at the set specific growth rate of 0.08, 0.05, and 0.02h^-1 after 12, 32, and 52h, respectively. Compared with exponential l-tyrosine feeding at the set specific growth rate of 0.08h^-1, the developed strategy obtained a 15.33% increase in l-phenylalanine production (l-phenylalanine of 56.20gL^-1) and a 45.28% decrease in l-tyrosine supplementation.