Inactivation of polycaprolactone depolymerase (cutinase) in Fusarium cultures by an extracellular protease

Abstract

Cultures of Fusarium moniliforme grown on polycaprolactone (PCL) or on cutin as a sole source of carbon and energy had low levels of detectable PCL depolymerase (cutinase) activity in the supernatant medium. A small peak of depolymerase activity was observed after hyphal accumulation had ceased, but this activity soon declined. The low level of the peak of activity and its decline were attributable to proteolytic inactivation of the depolymerase. A decrease in the pH of cultures coincided with the appearance of protease activity in the supernatant at about the same time as the appearance of the transient peak of depolymerase activity. Addition of protease substrates (bovine serum albumin, casein) to the culture at this time caused a dramatic although temporary increase in PCL depolymerase activity. The same effect was seen for cultures of F. solani pisi. Use of a different buffer system for the medium prevented a drop in pH and resulted in higher and stable levels of PCL depolymerase activity.