The intracellular pH (pHi) of a,dicarboxylic acid producing Candida tropicalis was determined by a fluorescence technique using the pH-sensitive fluorescent probe 5(6)-carboxyfluorescein diacetate. Fermentations with n-tridecane substrate to produce a,-tridecanedioic acid were carried out in a 5-l bioreactor in which growth and production were separated. During the growth phase, the measured pHi values were varied from 5.65 to 6.15 in all the experiments performed under different constant pH-operating conditions. The specific rates of growth, sucrose consumption, CO2 production, and O2 consumption were correlated with pHi. Cytochrome P450 monooxygenase (P450), which catalyzes n-alkane hydroxylation, was only slightly expressed during the growth phase. During the first 6h of the production phase, P450 activity was induced rapidly accompanying higher pHi. A much higher level of P450 activity was observed at pHi of 6.55

The effects of oligosaccharide from Fusarium oxysprum on secondary metabolisms in suspension cultures of Taxus chinensis var. mairei were investigated by detecting the oxidative burst (OB) signals using an Electron Paramagnetic Resonance (ESR) spectrometer. The oxidative burst signals induced by oligosaccharide gradually increased to a maximum at 4h. Phenylalanine ammonia lyase (PAL) and polyphenol oxidase (PPO) activities were respectively 2 and 4 times higher than those of control, and large amount of phenolics were accumulated in culture medium. Two times of obvious increase in taxol production was observed, which was in accordance with the two times of elicitation of oxidative burst signals. The dependence of taxol production on the intensity of OB signals obeyed a modified Logistic curve. It was inferred that the syntheses of the side chain and nucleus of taxol were enhanced at low and high intensities of OB signals, respectively.

A non-linear cascade model is proposed to describe the signal transduction pathway in suspension cultures of Taxus chinensis var. mairei induced by an oligosaccharide from Fusarium oxysporum. The oxidative burst intensity, which was defined as the amount of the free radicals including superoxide anion (O2·), H2O2 and OH− and measured by ESR spectrometry, was used as the signal characteristic and the theory of electronic signal transduction cascade was then applied to derive the initial model. The model shows that the signal transduction cascade process is composed of three cascade nets, represented by the phosphorylation of a G-protein, activation of an ion channel and phospholipase C, and phosphorylation of protein kinase C. The three reactions were calculated as beginning at 30.5, 48.8 and 141.4min after elicitation, and the maximum variation rates of the signal intensity in the three nets occurred at 43.2, 80.6 and 192.6min, respectively. The validity of the model predictions was verified by experimental data.

A structured kinetic model was established to describe the process of Taxol formation in suspension cultures of Taxus chinesis var. mairei induced by an oligosaccharide from Fusarium oxysporum. In this model, the role of intracellular starch as a storage carbon source had to be taken into account. Substrate uptake, culture growth, cell respiration, and secondary metabolites, predicted by the model, agreed with those obtained experimentally. The effective factors of oligosaccharide elicitation, ηe,j, defined as the ratio of the parameter values in the system with oligosaccharide to those in control, reflected the effects of the oligosaccharide on cell growth and Taxol production.

Separation of l-glutamine (l-Gln) from Gln fermentation broth by nanofiltration (NF) was investigated with NTR7450 NF membrane. The effects of various experimental parameters such as transmembrane pressure, pH and concentration of broth on the rejection of l-Gln and l-glutamate (l-Glu) showed that NTR7450 was able to effectively separate l-Gln and l-Glu when the appropriate conditions were chosen. Moreover, the rejection of l-Gln and l-Glu in a single amino acid solution was also studied with the variation of pH, concentration, and physicochemical parameters. It was demonstrated that deviations in the rejection of fermentation broth from a single l-Gln or l-Glu solution were mainly caused by the complex ionic composition of the real fermentation broth.