Effects of different glycerol feeding strategies on S-adenosyl-l-methionine biosynthesis by P(GAP)-driven Pichia pastoris overexpressing methionine adenosyltransferase.

Methionine adenosyltransferase (MAT) was overexpressed within Pichia pastoris employing the promoter of glyceraldehyde-3-phosphate dehydrogenase gene (P(GAP)), to biosynthesize S-adenosyl-l-methionine (SAM). Effects of five glycerol feeding tactics on MAT activity were first investigated. Strategies A-C were based on limited feeding correlated with dissolved oxygen (DO) at 50.0%, 25.0% and 0.0%, respectively. For strategies D and E, unlimited supplementation was executed by pulsed feeding mode. Gradual decline (2-0%) (w:v) of the residual glycerol level was shown between any two pulses in strategy D, while a nearly stable content (2%) throughout fed-batch cultivation with strategy E. With shifting strategies A-E in alphabetical order, gradual improvements of MAT activities were achieved, with the maximum of 9.05Ug(-1) dried biomass for strategy E, since the specific glycerol consumption rate (F(G)) ascended due to the elevated specific oxygen uptake rate (qO(2)). The success was ascribed to the enhancement of oxygen transfer rate (OTR), because 2% glycerol improved oxygen saturation content in broth (C*) and volumetric oxygen transfer coefficient (k(L)a). Strategy E also led to the highest values of ATP and biomass besides MAT. Consequently, the highest SAM yield and volumetric level were obtained at 0.058gg(-1) and 9.26gl(-1), respectively.

[Influence of Mn2+ on the biotechmycin fermentation].

The effect of Mn2+ on the biotechmycin fermentation by Bioengineered strain WSJ-l-195 was studied. In the fermentation process, Mn2+ could improve the biological potency significantly, especially when Mn2+ concentration was 5 mmol/L added at 24 h. The pH profile of fermentation broth decreased gradually after 5 mmol/L Mn2+ supplemented at 24 h, and PMV was lower than that of the control sample. Further research about the influence of Mn2+ on the biosynthesis of biotechmycin was carried out in the aspect of organic acids. The results showed that concentrations of organic acids in a fermentation with 5 mmol/L Mn2+ supplemented at 24 h had been changed greatly, especially the concentration of propionic acid, of which the highest value was about 6 times as that in the control sample at 84 h. In addition, it was found that the yield of biotechmycin could be improved significantly with tiny amount of propionic acid added. Therefore, it can be concluded that Mn2+ has profound influence on the biosynthesis of biotechmycin: it enriches the biotechmycin precursor pool such as propionic acid and thus improves the yield of biotechmycin.