Maintenance of penicillin G acylase expression by B. megaterium: preservation methods and activity recovery

this work reports the influence of different culture preservation methods on the production of penicillin g acylase (pga) by bacillus megaterium atcc 14945. the initial stock culture, presenting pga activity of 97 iu l-1, was preserved for two years using different procedures: monthly subculturing and storage in refrigerator (s), freeze-drying using skim milk 10%, plus inositol 5% as cryoprotectors (l1), freeze-drying using sucrose 7%, plus peptone 7% (l2), and freezing with glycerol 10% (f). after cultivations at standard operational conditions, different values of enzyme activity were obtained: 56 iu l-1 for monthly subculturing (s), 15-41 iu l-1 for freeze-dried cells and frozen spores. all the tested methods have failed in preserving the pga expression. among all tested cultures, s presented the highest specific activity, and was used to prepare a standard inoculum in cryovials (-50oc, frozen spores in a 20% glycerol solution). by cultivation of this inoculum under different conditions, it was found that pga activity raised to 128 iu l-1 when 0.4 g l-1 of salts was added to the medium.