The Cellulolytic Activity of Six Oomycetes

Abstract

A review of the literature has shown a need for further investigation of the physiology of aquatic Phycomycetes and in particular the Oomycetes. Most investigations have dealt primarily with their morphology, taxonomy, and geographical distribution (1, 5, 6). However, their importance in decomposition and simplification of organic matter, especially when compared with bacteria and protozoa, is still an unanswered question (6). One of the most important structural polysaccharides of the plant kingdom is cellulose. The degradation of cellulose is often discussed in connection with the action of fungal parasites. The ability of Oomycetes to produce cellulolytic enzymes has been infrequently investigated (1, 5, 6). In addition, most studies that are reported lack quantitative data. Unestam (7), in his quantitative study, reported no cellulolytic activity of a Pythium sp. and Saprolegnia sp. incubated in shake and stationary media containing cellulose. Preliminary investigations, of growth on a semichemically defined medium, indicated that Pythium mamnmillatum Meur, P. dissoticum Drechsler, Pythium sp., Achlya americana Humphrey, Saprolegnia parasitica Coker, and Thraustotheca clavata (de Bary) Humphrey could be utilized for a quantitative investigation of the cellulolytic activity of Oomycetes. Dr. C. L. Fergus supplied isolates Pythium mammillatum, England 1962; Pythium sp., Vaartaja; P. dissoticum, W. A. Campbell 919-2; Thraustotheca clavata, ATCC 14555. Isolates of Achlya americana and Saprolegnia parasitica were obtained from the American Type Culture Collection as ATCC 14565 and ATCC 22284 respectively. The cellulolytic activity of the fungi was determined by modifying the method described by Fergus (3). First, the ability of these six Oomycetes to utilize an insoluble form of cellulose was investigated. Filter paper (Whatman No. 3, 5.5 cm in diam) was folded, oven-dried, and weighed. Two pieces were placed in each of a number of 250-ml Erlenmeyer flasks containing 50 ml of a medium of the following composition: K2HPO4,