Induction and Catabolite Repression of Cellulase Synthesis in the Thermophilic Fungus Sporotrichum thermophile

Abstract

SUMMARY: A strain of Sporotrichum thermophile (var. 2), grown in submerged culture at 44°C, decayed crystalline cellulose by the secretion of cellulolytic enzymes into the culture medium. Dialysed culture filtrates, after growth on cellobiose, were also effective in degrading crystalline cellulose (Avicel). Cellulase, measured viscometrically with carboxymethylcellulose as substrate and therefore referred to as CM-cellulase, was induced by cellulose, glucomannan, cellobiose and, to a limited extent, by laminaribiose and cellobionic acid. Low CM-cellulase activities were also detectable when the organism was grown on other carbon sources. In culture media supplemented with readily metabolized non-inducing substrates, such as glucose, CM-cellulase activity did not increase after their exhaustion indicating that no derepression of constitutive CM-cellulase occurred. CM-cellulase synthesis induced during growth on cellobiose was strongly inhibited, although not completely suppressed, by glucose and other carbon sources. In cultures grown on glucose and cellobiose, glucose was utilized first and CM-cellulase synthesis was repressed; cellobiose utilization occurred only after glucose exhaustion and triggered CM-cellulase formation. When glucose was added to a culture growing on cellobiose, further utilization of the latter was prevented and CM-cellulase synthesis was inhibited. The use of glucose analogues gave some indications that cellobiose did not compete with glucose for the same transport carrier and that glucose catabolism was a prerequisite for the inhibition of CM-cellulase synthesis.