Suberin-grown Fusarium solani f. sp pisi generates a cutinase-like esterase which depolymerizes the aliphatic components of suberin

Abstract

Fusarium solani pisi isolate T-8 was found to grow with suberin from potato tuber periderm as the sole source of carbon. The extracellular fluid from such cultures catalysed the hydrolysis of p-nitrophenyl butyrate and radioactive apple cutin. The major portion of this esterase was bound to the suberin-containing mycelial mat from which the activity could be washed out with a 0·4% Triton X-100 solution. All of this esterase activity was contained in two isozymes which were purified by a passage of the Triton wash through QAE-Sephadex followed by ion exchange chromatography with SP-Sephadex. Both isozymes were homogeneous as judged by polyacrylamide gel electrophoresis with or without SDS. Each showed a molecular weight of 23 000. Analysis of the aliphatic components released by the esterase from suberin by combined GLC/MS showed that all classes of monomers were released by the esterase. The two enzymes were very similar in their catalytic properties and amino acid composition to two isozymes of cutinase isolated from the extracellular fluid of the same fungus grown on apple cutin. The esterases had one disulphide bridge and no free SH group just as previously noted for fungal cutinases. Ouchterlony double diffusion analyses showed that the two esterases isolated from suberin-grown cells cross-reacted with complete fusion of the precipitin lines when tested with antibodies generated against the two cutinases generated by cutin-grown cells. These results strongly suggest that F. solani pisi generates extremely similar, if not identical, polyesterases to degrade cutin and suberin when these polymers constitute the sole carbon source.