Regulation of Cellulase Formation in Clostridium thermocellum

Summary: True cellulase activity (i.e. degradation of crystalline cellulose) was markedly derepressed when cellobiose-grown cells were transferred to fructose or sorbitol, especially while the cells were adapting over many hours to these carbon sources. On the other hand, the long lag phase on glucose was not accompanied by derepression. Transfer to cellobiose resulted in low cellulase production. Growth on crystalline cellulose derepressed cellulase production. Addition of cellobiose (the preferred carbon source for growth) to cells adapting to fructose caused a rapid burst of growth and cessation of cellulase synthesis. After cells had adapted to growth on fructose or sorbitol, repression set in and, after a number of transfers, growth on these carbon sources yielded cellulase at a level even lower than with cellobiose or glucose. It appears that rapid growth on a soluble sugar such as cellobiose causes carbon source repression which is relieved during slow growth on crystalline cellulose or during the growth lag on fructose or sorbitol. The reason for the lack of cellulase derepression during the growth lag on glucose is unexplained.