排序方式: 共有46条查询结果,搜索用时 15 毫秒
41.
42.
Cybernetic modeling of the cephalosporin C fermentation process by Cephalosporium acremonium 总被引:2,自引:0,他引:2
A cybernetic mathematical model has been developed to describe the production of cephalosporin C. In developing the model, diauxic behavior of substrate consumption, morphological differentiation of cells, and catabolite repression of cephalosporin C production by the preferred substrate, glucose, were considered. The proposed model was tested on the experimental data from the literature and could adequately describe the morphological differentiation of cells, the sequential utilization of carbon sources and the production of cephalosporin C. It could be a useful tool to optimize the production of cephalosporin C by Cephalosporium acremonium in batch, fed-batch or continuous operations. 相似文献
43.
The bacterial endosymbiont of aphids, Buchnera aphidicola, often provides amino acids to its hosts. Plasmid amplification of leucine (leuABCD) and tryptophan (trpEG) biosynthesis genes may be a mechanism by which some Buchnera over-produce these nutrients. We used quantitative polymerase chain reaction to assess the leuABCD/trpEG copy variability within Uroleucon ambrosiae, an aphid with a wide diet breadth and range. Both leuABCD and trpEG abundances are: (i) similar for aphids across 15 populations, and (ii) low compared to Buchnera from other aphid species (particularly trpEG). Consequently, the plasmid location of trpEG combined with Buchnera's chromosomal polyploidy may functionally limit, rather than increase, tryptophan production within Uroleucon ambrosiae. 相似文献
44.
The objective of this study is to improve cephalosporin C (CPC) production by optimization of medium and culture conditions.
A statistical method was introduced to optimize the main culture medium. The main medium for CPC production was optimized
using a statistical method. Glucose and corn steep liquor (CSL) were found to be the most effective factors for CPC production.
Glucose and CSL were optimized to 2.84 and 6.68%, respectively. CPC production was improved 50% by feeding of 5% rice oil
at day 3rd and 5th day during the shake flask culture ofC. acremonium M25. The effect of agitation speeds on CPC production in a 2.5-L bioreactor was also investigated with fed-batch mode. The
maximum cell mass (54.5 g/L) was obtained at 600 rpm. However, the maximum CPC production (0.98 g/L) was obtained at 500 rpm.
At this condition, the maximum CPC production was improved about 132% compared to the result with batch flask culture. 相似文献
45.
46.
Isopenicillin N synthase (IPNS) catalyses a key step in the penicillin and cephalosporin biosynthetic pathway which involves the oxidative cyclisation of the acyclic peptide delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine (ACV) to isopenicillin N. Based on crystallographic evidence from the Aspergillus nidulans IPNS crystal structure complexed with the substrate ACV (Roach et al. (1997) Nature 387, 827-830), we were able to provide mutational evidence for the critical involvement of the conserved R-X-S motif in ACV binding in IPNS. The crystal structure further implicated arginine-87 in the binding of the aminoadipyl portion of ACV. Thus, in this study, the site-directed mutagenesis of the corresponding arginine-89 in Cephalosporium acremonium IPNS (cIPNS) was performed to ascertain its role in cIPNS. Alteration of arginine-89 to five amino acids from different amino acid groups, namely lysine, serine, alanine, aspartate and leucine, was performed and no activity was detected in all the mutants obtained when enzyme bioassays were performed. Furthermore, the solubility of the mutants was considerably lower than the wild-type cIPNS after expression at 37 degrees C, but could be recovered when the expression temperature was lowered to 25 degrees C. This suggests that arginine-89 could be critical for the activity of cIPNS due to its involvement in ACV binding and the solubility of wild-type enzyme. 相似文献