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Aromatic amino acid synthesis performance of bacillus acidocaldarius

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2004
Kocabaş, Pınar
In this study, the effects of bioprocess operation parameters on aromatic amino acid synthesis performance of Bacillus acidocaldarius were investigated. Firstly, in laboratory scale shake-bioreactors, a defined medium was designed in terms of its carbon and nitrogen sources, to achieve the highest cell concentration. Thereafter, the effects of bioprocess operation parameters, i.e., pH and temperature were investigated; and the optimum medium contained (kg m-3): fructose, 8; (NH4)2HPO4, 5; CaCl2, 0.2; KH2PO4, 2; NaH2PO4.2H2O, 7.318; Na2HPO4, 0.0438; Mg(CH3COO)2.4H2O, 87₉10-3 ; 1 , MgSO4.7H2O; 2₉10-3, FeSO4.7H2O; 2₉10-3, ZnSO4.7H2O; 15 ₉10-5, MnSO4.H2O; 2₉10-5, CuSO4.5H2O with pH0 =5, T=55?C, N=175 min-1. In this medium, the bacteria produced L-tryptophan at the highest concentration of 0.204 kg m-3 and L-phenylalanine at a maximum concentration of 0.0106 kg m-3 with no L-tyrosine production. Finally the fermentation and oxygen transfer characteristics of the bioprocess were investigated in 3.0 dm3 pilot scale bioreactors. The effects of oxygen transfer were investigated at four different conditions at the parameters air inlet rates of QO/VR =0.2, and 0.5 vvm, and agitation rates of N= 250, 500, 750 min-1. The effect of pH was investigated at pH=5 uncontrolled and controlled operations. The variations in cell, fructose, amino acid and organic acid concentrations with the cultivation time; and using the dynamic method, the oxygen uptake rate and the liquid phase mass transfer coefficient values throughout the growth phase of the bioprocess; the yield and maintenance coefficients were determined. The aromatic amino acids produced at the highest and the least amount and frequency were L-tryptophan and L-tyrosine, respectively. The highest L-tryptophan production, 0.32 kg m-3 in 17 hour was at 0.2 vvm and 500 min-1. Among all operations, the highest L-tryptophan was