REPRESSION AND INACTIVATION OF ALPHA-AMYLASE IN THERMOMONOSPORA SPECIES DURING GROWTH AN CELLOBIOSE

Thermophilic actinomycetes establish themselves as numerically dominan t bacterial populations in selected high temperature environments by v irtue of their exoenzymic ability to degrade the complex polysaccharid es in thermogenic plant biomass. When Thermomonospora curvata and Ther momonospora fusca were grown on a mixture of cellulose and starch in m ineral salts minimal medium, alpha-amylase was repressed via inhibitio n of maltose uptake by cellobiose. Addition of cellobiose to exponenti al phase cells growing on maltose or maltotriose triggered rapid degra dation of extant amylase in the culture fluid of wild-type cells, but not in a protease-deficient mutant of T. fusca. A serine protease puri fied from T. fusca caused inactivation of the amylase in culture fluid of the mutant when added at a concentration approximating to that of the wild-type strain. The chelating agent, EDTA, accelerated inactivat ion by the protease, while the presence of calcium or amylase reaction products protected the amylase. Therefore, during growth in an enviro nment containing multiple polysaccharides. these thermophiles control the levels of their extracellular depolymerizing enzymes via both indu cer exclusion and proteolytic inactivation.