3.4 Effects of nucleotides on growth and production
Except for amino acids, the deficient synthesis of nucleotides (uracil and adenine) is also commonly used screening markers. The absence or insufficiency of nucleotides will inevitably affect cell growth, considering their essential roles in translation process as three nucleotide codons in the central rule. We investigated the effects of exogenous addition of nucleotides with different concentrations on the growth and production in two nucleotide deficient strains (ura3 Δ and ade2 Δ). As 100 mg/L of supplements are sufficient (Figure S3), lower concentrations of 20, 60, and 100 mg/L were utilized to determine the growth and production capacity of the strains (Figure 5).
These two deficient strains possessed a similar characteristic in required amounts of nucleotides. The performances of the strains were similar to the control strain when only 60 mg/L uracil or adenine was added, and the increased concentrations did not further improved cell growth (Figure 5A, B). FFA titers of the strain ura3 Δ supplemented with 60 mg/L and 100 mg/L uracil were about 90% of that in control strain (Figure 5C). In contrast, FFA titers of strainade2 Δ were 60% and 90% of that of control strain, respectively (Figure 5D).