Unique features of several microbial α-amylases active on soluble and native starch

Abstract

Starch is the main energy store of major agricultural crops such as corn, potato, rice and wheat. Various amylase type enzymes are used to convert cooked starch to glucose that goes into bioethanol fermentation. Only a few amylase type enzymes have been described that can act on the starch granule itself. Granular starch has a complex crystalline structure that prevents most amylases to directly act on it. In this PhD thesis the action of several amylases on native granular starch was studied in detail. From the wastewater treatment plant of a potato starch factory of AVEBE, a microbial strain specialized in the degradation of potato starch granules was isolated. This isolate possesses a multi domain amylase with several starch binding and fibronectin modules, enabling a rapid degradation of potato starch granules. Deletion of multiple domains resulted in a loss of the granule degrading capacity of this amylase. The modular organization was not found in an amylase obtained from a microbial strain living in a sea anemone from Jellyfish lake, Kakaban Island, Indonesia. This amylase showed very little activity towards granular starch, which is not surprising as this lake has no starch. The substrate for this amylase enzyme is very likely glycogen present in the sea anemone. These results demonstrate that starch granules are inert and require specialized amylase enzymes to be completely degraded. Such special amylase enzymes could be used in a non-cooking starch conversion process, reducing the amount of energy required in the production of glucose syrups for bioethanol fermentation