(v/v)/min gas flow rate of 24-48h at 29±1℃. The addition of the sieve plates in the riser of the external-loop airlift bioreactor increased productivity. After 48 h, under optimized operation conditions, crude protein productivity with one sieve and two sieves were 13.6mg/mL and 13.7mg/mL, respectively, comparing 12.7mg/mL without sieves in the airlift bioreactor and 11.7mg/mL in the in the 10-L mechanically stirred tank bioreactor. It is feasible to operate the external-loop airlift bioreactors and possible to reduce the production cost for microbial biomass production from the rice straw hydrolysate.

Immobilized Pseudomonas sp. HZ519 cells have been used for transformation of validamycin A to valienamine and the degradation pathway of validamycin A by Pseudomonas sp. HZ519 has also been studied. Substrate inhibition in immobilized cell system was avoided. An average of 8.6gL-1 valienamine concentration was obtained when concentration of validamycin A was increased up to 120gL-1. Through a treatment of the immobilized cells with 0.3mol/L-1 substrate, the activity of the immobilized cells was increased distinctly. Compared with free cells, the productivity of valienamine by CA-immobilized cells was improved about three times. The reusability of the immobilized cells was evaluated with repeated/batch degradation experiments. The Tiele modulus was obtained from the experimental effectiveness factor. The result showed that the degradation process in the immobilized system was governed by intraparticle diffusion and chemical reaction.

A reversed-phase high-performance liquid chromatography method for the quantitative analysis of valienamine in the microbial degradation of validamycin A, using a procedure for pre-column derivatization of valienamine with p-nitrofluorobenzene is described. Valienamine in the broth was first isolated with the ion-exchange method. The optimized conditions for the derivatization were the reaction time 30 min and reaction temperature 100℃. With the mobile phases consisting of acetonitrile-water (12∶88)(eluent A) and methanol (eluent B), the gradient was carried out with 100% of A for 15 min and then 100% of B for another 10min. The parameters in the process were the flow rate of the mobile phase 1.0ml/min, the injection volume 20μl, the column temperature 40℃ and wavelength of ultraviolet detection 398nm in all runs. A good linearity was found in the range of 0.5-150.0μg/ml. Both intra-and inter-day precisions of valienamine, expressed as the relative standard deviation, were less than 9.4%. Accuracy, expressed as the relative error, range from −0.5 to 2.7%. The mean absolute recovery of valienamine at three different concentrations was 94.2%. The method was proved suitable for the study on the process of microbial degradation of validamycin A to produce valienamine.

Different cation resins, IR-120 and HZ-001, were used as catalysts to prepare validoxylamine A through validamycin A degradation. Herein, influences of reaction time, reaction temperature, resin usage, initial validamycin A concentration, as well as external and internal diffusion limitation, on the degradation ratio of validamycin A were studied. Results demonstrated that validamycin A could almost completely be degraded into validoxylamine A under optimized operation conditions of 5.0% (w/v) resin usage, 1.0%(w/v) initial validamycin A concentration, agitation speed of 200 rpm, and heating at 100℃ for 5h.