Hyperthermostable, Ca2+-Independent, and High Maltose-Forming α-Amylase Production by an Extreme Thermophile Geobacillus thermoleovorans: Whole Cell Immobilization

摘要

The synthesis of extracellular α-amylase in Geobacillus thermoleovorans was constitutive. The enzyme was secreted in metabolizable carbon sources as well as non-metabolizable synthetic analogues of glucose, but the titers were higher in the former than that in the latter. G. thermoleovorans is a fast-growing facultatively anaerobic bacterium that grows under both aerobic and anaerobic conditions and produces an extracellular amylolytic enzyme α-amylase with the by-product of lactic acid. G. thermoleovorans is a rich source of various novel thermostable biocatalysts for different industrial applications. α-Amylase synthesis was subject to catabolite repression in the presence of high concentrations of glucose. The addition of cAMP to the medium containing glucose did not result in the repression of α-amylase synthesis. The addition of maltose (1%) to the starch arginine medium resulted in a twofold enhancement in enzyme titers. Polyurethane foam (PUF)-immobilized cells secreted α-amylase, which was higher than that with the free cells. PUF appeared to be a better matrix for immobilization of the thermophilic bacterium than the other commonly used matrices. The repeated use of PUF-immobilized cells was possible over 15 cycles with a sustained α-amylase secretion. The use of this enzyme in starch saccharification eliminates the addition of Ca2+ in starch liquefaction and its subsequent removal by ion exchangers from the product streams.