Starch‐like exopolysaccharide produced by the filamentous fungi Ophiostoma ulmi and O. novo‐ulmi

Abstract

SummaryThis paper describes the chemical and biochemical properties of exopolysaccharides (EPS) produced by Ophiostoma ulmi and O. novo‐ulmi isolates, the Dutch elm disease (DED) fungi. Some of EPS have been considered as pathogenicity factor in the DED complex. The selected isolates grow well and produce EPS in a medium containing various types of carbon and nitrogen sources. EPS obtained from potato dextrose broth (PDB) medium appeared to be opaque, firm and stained purple blue with iodine‐potassium iodide solution, whereas those from yeast extract (YE) medium were less opaque, jelly‐like and remained unchanged in iodine solution. The selected fungal isolates produced much higher molecular weight EPS from the medium containing YE than from PDB. The results of this study suggest that high molecular weight compounds produced by O. ulmi (W9) and O. novo‐ulmi (R136) are not involved in DED pathogenesis. Spectrometric analysis of acid‐digested EPS obtained from PDB and YE revealed the presence of a monomer similar to glucose used as a standard. Thin layer chromatography indicated that glucan‐1,4‐α‐glucosidase (glucoamylase) only hydrolyses EPS from PDB media and releases glucose. The results strongly indicate that isolates of O. ulmi and O. novo‐ulmi produce starch‐like EPS from PDB medium. The EPS obtained from YE medium lacked this characteristic. The biological significance and the potential use of these EPS are discussed.