Continuous alpha-amylase production using Bacillus amyloliquefaciens adsorbed on an ion exchange resin

Abstract

A method for the continuous production of extracellular alpha amylase by surface immobilized cells of Bacillus amyloliquefaciens NRC 2147 has been developed. A large-pore, macroreticular anionic exchange resin was capable of initially immobilizing an effective cell concentration of 17.5 g DW/1 (based on a total reactor volume of 160 ml). The reactor was operated continuously with a nutrient medium containing 15 g/l soluble starch, as well as yeast extract and salts. Aeration was achieved by sparging oxygen enriched air into the column inlet. Fermentor plugging by cells was avoided by periodically substituting the nutrient medium with medium lacking in both soluble starch and yeast extract. This fermentor was operated for over 200 h and obtained a steady state enzyme concentration of 18700 amylase activity units per litre (18.7 kU/l), and an enzyme volumetric productivity of 9700 amylase activity units per litre per hour (9.7 kU/l-h). Parallel fermentations were performed using a 2 l stirred vessel fermentor capable of operation in batch and continuous mode. All fermentation conditions employed were identical to those of the immobilized cell experiments in order to assess the performance of the immobilized cell reactor. Batch stirred tank operation yielded a maximum amylase activity of 150 kU/l and a volumetric productivity of 2.45 kU/l-h. The maximum cell concentration obtained was 5.85 g DW/l. Continuous stirred tank fermentation obtained a maximum effluent amylase activity of 6.9 kU/l and a maximum enzyme volumetric productivity of 2.73 kU/l-h. Both of these maximum values were observed at a dilution rate of 0.345 l/h. The immobilized cell reactor was observed to achieve larger volumetric productivities than either mode of stirred tank fermentation, but achieved an enzyme activity concentration lower than that of the batch stirred tank fermentor.