Enhancement of docosahexaenoic acid production by Schizochytrium sp. using a two-stage oxygen supply control strategy based on oxygen transfer coefficient.

AIMS: To improve the yield and productivity of docosahexaenoic acid (DHA) by Schizochytrium sp. in terms of the analysis of microbial physiology. METHODS AND RESULTS: A two-stage oxygen supply control strategy, aimed at achieving high concentration and high productivity of DHA, was proposed. At the first 40 h, K(L) a was controlled at 150·1 h(-1) to obtain high µ for cell growth, subsequently K(L) a was controlled at 88·5 h(-1) to maintain high q(p) for high DHA accumulation. Finally, the maximum lipid, DHA content and DHA productivity reached 46·6, 17·7 g l(-1) and 111 mg l(-1) h(-1), which were 43·83%, 63·88% and 32·14% over the best results controlled by constant K(L) a. CONCLUSIONS: This paper described a two-stage oxygen supply control strategy based on the kinetic analysis for efficient DHA fermentation by Schizochytrium sp. SIGNIFICANCE AND IMPACT OF THE STUDY: This study showed the advantage of two-stage control strategy in terms of microbial physiology. As K(L) a is a scaling-up parameter, the idea developed in this paper could be scaled-up to industrial process and applied to other industrial biotechnological processes to achieve both high product concentration and high productivity.

The effect of AmtR on growth and amino acids production in Corynebacterium glutamicum.

AmtR, the master regulator of nitrogen control in Corynebacterium glutamicum, plays important roles in nitrogen metabolism. To investigate the influence of AmtR on amino acids production in C. glutamicum ATCC 13032, the amtR deletion strain C. glutamicum Q1 was constructed and cultured in modified CGXII minimal medium for 60 h. The ammonium consumption rates as well as amino acids production of both strains cultured in modified CGXII minimal medium were determined. The amtR deletion in C. glutamicum caused an obvious growth defect in the exponential growth phase, but both strains had the same biomass in the stationary phases. Maybe the less alpha-oxoglutarate was used for the tricarboxylic acid cycle to influence the growth of strains. During 12 h, the rate of ammonium consumption and the concentration of Glu, Pro, Arg and Ser were higher but Asp, Gly, Ile, Leu, Lys were lower in the mutation strain. During 48 h, the Q1 had higher levels of Asp, Lys, Pro, Ala and Val,and lower levels of Glu, Arg, Leu and Ile, compared to the wild. The more Glu was synthesized by the activated GS/GOGAT pathway in Q1, and then the accumulation of relative amino acids (Pro, Arg and Ser) were up-regulated within 12 h growth. After 48 h growth, the amtR deletion obviously influenced accumulation of Ala, Asp and Pro. The amtR deletion could influence the growth and amino acids production, which could be useful to the production of amino acids.

[Study on the optimal conditions in simultaneous reaction and separation for L-malic acid production].

Based on the principle of coupling reaction and separation process, free cells containing fumarase were used for producing L-malic acid. The calcium fumarate was used as substrate to produce calcium malate directly. This new method was more advantageous than the traditional immobilized cells conversion system in aspects such as simple equipment and operation, high conversion efficiency and the yield of product. The results showed that at reaction temperature 40 degrees C, pH7.0-7.5, reaction time 20-28 h, the conversion efficiency was up to 99.9% and about 3.2 kg calcium fumarate was converted to calcium malate per liter enzyme suspension. Also, L-malic acid produced in free fumarase system satisfied USP criterion, the residual fumaric acid was less than 0.1% and the cost was approximately to that of DL-malic acid produced by chemical synthesis.