Chapter IX — 135 — Yeasts and Molds 



parasitic or saprophytic fungi, another problem which invites attention. 

 Most of the fungi described by Bargiioorn and Linder (1944) were 

 isolated from wood or rope which had been submerged in the sea. His- 

 tological examination of their natural substrata showed that the fungi 

 penetrate and ramify the cell walls of wood and cordage fibers, inducing 

 decay by enzymatic hydrolysis of the cellulose and other cell wall con- 

 stituents. The fungi readily utilized cellulose, pectin, and starch under 

 experimental conditions. Maltose, galactose, xylose, and asparagine were 

 also utilized. Growth was vigorous and fairly rapid on wood flour agar. 

 Many of the fungi attacked lignin. The evidence is convincing that fungi 

 cause the deterioration of cordage libers and wood under marine condi- 

 tions. 



Importance of fungi in lakes : — In reviewing the literature on the sub- 

 ject, Weston (1941) states that there are between 700 and 800 species of 

 Phycomycetes which are definitely aquatic, besides many others which, 

 though normally terrestrial, are capable of living in water. In this latter 

 category are several species of Penicillium and Fusarium. Relatively few 

 species of Ascomycetes are adapted to aquatic life. 



Aquatic fungi are capable of activity and survival over a wide range of 

 environmental conditions, being found in inland waters throughout the 

 world. They grow equally well in direct sunlight or darkness. Certain 

 ones are active at temperatures ranging from 1° to 33° C, and in water as 

 acidic as pK 3.2 or as alkaline as pH 9.6. Most fungi require free oxygen. 



Aquatic fungi are both saprophytic and parasitic. Their ability to 

 break down pectins, hemicelluloses, and cellulose is widespread. In at- 

 tacking organic matter, fungi may influence the pH, oxygen content, and 

 other chemical properties of the water. Most plants and animals living 

 in lakes are susceptible to parasitism by aquatic fungi. Serious fungal 

 epidemics among diatoms and desmids have been reported. The eggs of 

 some animals are destroyed by fungi, and such organisms may also cause 

 extensive infections of fresh-water fish. Fungi may be a limiting factor 

 in aquatic biology. 



Many aquatic animals such as protozoans, rotifers, coelenterates, 

 arthropods, etc., devour fungi spores from which they derive nourishment. 



According to Weston (1941), water fungi are "ubiquitous, abundant, 

 versatile, hardy, and efficient, playing a significant part in the complexly 

 interwoven pattern of biologic interaction in inland waters; as sapro- 

 phytes in manifold capacities unceasingly active in the essential degra- 

 dation of complex materials; and as parasites ever preying inconspicuously 

 on the major groups of plants and animals important in hydrobiology, 

 and occasionally so severely destructive as to reduce productivity." 



Numerous species of Phycomycetes, which parasitize the eggs, em- 

 bryos, and adult forms of various aquatic animals, are described by 

 Sparrow (1943). Fresh-water algae, diatoms, and other aquatic plants 

 are likewise infected. Some of the Phycomycetes are responsible for 

 infections of epidemic proportions. For example, Rhizophydium agile has 

 been reported to destroy up to 75 per cent of the Chroococcus turgidus cells 

 in the field and in gross cultures. Attention is directed to the extensive 

 bibliography on aquatic Phycomycetes compiled by Sparrow (1943). 



