A second polycaprolactone depolymerase from Fusarium, a lipase distinct from cutinase

Polycaprolactone (PCL), a synthetic polyester with applications in biodegradable plastics, is degraded by a variety of microorganisms, including fungal phytopathogens. These pathogens secrete cutinase, which hydrolyzes cutin, the polyester structural component of plant cuticle, releasing ω-hydroxy fatty acids that induce cutinase synthesis. Our laboratory previously reported that growth of Fusarium solani on PCL requires cutinase, which is active as a PCL depolymerase and induced by the products of its action on PCL. A mutant strain of F. solani in which the cutinase gene is deleted was unable to grow on PCL and did not secrete PCL depolymerase activity in the media tested. It is now shown that this mutant produces a PCL depolymerase in media containing lipase inducers. Wild-type strains also produce this second PCL depolymerase, which is induced by Tween 80 and tributyrin, but not by PCL or cutin. The second depolymerase shows interfacial activation, indicating that it is a lipase. PCL may thus be a substrate but not an inducer of depolymerases that degrade it, and screening microorganisms on medium with PCL as the sole source of carbon and energy may fail to reveal strains with active PCL depolymerases, because of the absence of an inducer. Surprisingly, Tween 80 induces both cutinase and lipase activities in wild-type F. solani. Received: 31 March 1998 / Received revision: 27 July 1998 / Accepted: 8 August 1998