Improving the biocatalytic performance of co-immobilized cells harboring nitrilase via addition of silica and calcium carbonate.

To improve nicotinic acid (NA) yield and meet industrial application requirements of sodium alginate-polyvinyl alcohol (SA-PVA) immobilized cells of Pseudomonas putida mut-D3 harboring nitrilase, inorganic materials were added to the SA-PVA immobilized cells to improve mechanical strength and mass transfer performance. The concentrations of inorganic materials were optimized to be 2.0% silica and 0.6% CaCO3. The optimal pH and temperature for SA-PVA immobilized cells and composite immobilized cells were both 8.0 and 45 °C, respectively. The half-lives of composite immobilized cells were 271.48, 150.92, 92.92 and 33.12 h, which were 1.40-, 1.35-, 1.22- and 1.63-fold compared to SA-PVA immobilized cells, respectively. The storage stability of the composite immobilized cells was slightly increased. The composite immobilized cells could convert 14 batches of 3-cyanopyridine with feeding concentration of 250 mM and accumulate 418 g ·L-1 nicotinic acid, while the SA-PVA immobilized cells accumulated 346 g L-1 nicotinic acid.

A new polysialic acid production process based on dual-stage pH control and fed-batch fermentation for higher yield and resulting high molecular weight product.

To determine the factors influencing the resulting molecular weight of polysialic acid (PSA), batch fermentations by using Escherichia coli were conducted. It was found that temperature and pH were significant factors affecting the PSA production and its resulting molecular weight. When pH was set at 6.4, temperature of 37 °C was suitable for cell growth and PSA production while 33 °C facilitated production of higher molecular weight of PSA. pH 6.4 was favorable for PSA production while pH 7.4 was good for higher molecular weight of PSA at 37 °C. Intramolecular self-cleavage of PSA might lead to relatively low molecular weight under mild acidic condition. Our data suggest that the PSA molecular weight is significantly affected by the pH condition rather than the temperature. It is concluded that the resulting PSA molecular weight not only depends on fermentation conditions but also relates to cell growth rate and PSA production rate. Higher PSA molecular weight was made when its production rate was faster than degradation rate. A novel two-stage pH control fermentation process for production of high molecular weight PSA was developed. At the first stage, pH was set at 6.4 to encourage cell growth and PSA production, whereas pH was set at 7.4 at the second stage to promote the formation of higher molecular weight PSA. PSA yield up to 5.65 g/L and its resulting molecular weight of 260 kDa was attained, the highest level ever reported.