Physiological parameters of growth in Saprolegnia parasitica coker

Abstract

Persistent bacteria were separated fromS. parasitica by means of the oligodynamic effect of a silver ring in a modification ofRaper's technique.

Inoculation of fungal cultures was by means of mycelial macerate.

Growth was measured by mycelial dry weight.

A chemically defined medium (standard medium) was developed which consisted of a mineral base (chlorides of magnesium, manganese, zinc, calcium, and iron) chelated with EDTA, supplemented with glucose, sodium glutamate, and methionine, and buffered at pH 7.0 with 0.01 M. KH₂PO₄.

Shaking culture methods supported increased growth rates and higher dry weight yields compared to stationary methods.

Excellent growth occurred between 15 to 30°C. in the standard medium and between pH 4.0 and 8.0 in the standard medium plus 0.01 M. sodium succinate and 0.01 M. TRIS used as additional buffers.

Significant phosphate toxicity was demonstrated at concentrations exceeding 0.05 M. Sodium succinate and TRIS, used as buffers at 0.01 M. each, were compatible withS. parasitica, whereas boric acid, sodium barbital, and sodium citrate inhibited growth under similar conditions.

Substitution of other carbon sources for glucose in the standard medium (on an equal carbon basis where possible) indicated that cellobiose, dextrin, fructose, glycerine, glycogen, sodium lactate, and soluble starch supported significantly heavier growth than did the standard medium minus glucose; glycogen had a greater yield than did the standard medium minus glucose; glycogen had a greater yield than the standard medium. Arabinose, dulcitol, galactose, inulin, lactose, mannitol, mannose, raffinose, rhamnose, sorbitol, sucrose, and xylose neither stimulated nor inhibited growth; however, growth inhibition was produced by α-ketoglutaric acid, sodium citrate, and sodium succinate.

When fatty acids and lipids were substituted for glucose (on an equal carbon basis where possible), only butter, lard, oleo, and palmitic acid supported heavier growth ofS. parasitica than the standard medium minus glucose. Stearicacid neither stimulated nor inhibited growth; acetic acid, butyric acid, formic acid, octanoic acid, and propionic acid significantly inhibited the growth of the fungus.

Various nitrogen sources were substituted for sodium glutamate in the standard medium (on an equal nitrogen basis where possible). Casein hydrolysate and gelatin produced yields higher than that developed in the standard medium; other nitrogen sources produced lesser yields but still greater than those from the standard medium minus sodium glutamate:

• a. Alanine, arginine, aspartic acid, and histidine (good nitrogen sources).

• b. Ammonium chloride, cysteine, leucine, serine, and urea (fair nitrogen sources).

• c. Glycine, isoleucine, lysine, methionine, phenylalanine, potassium nitrate, sodium nitrate, threonine, tryptophan, and valine (poor nitrogen sources).

When various sulfur sources were substituted for methionine in the standard medium (on an equal sulfur basis), only cysteine and cystine produced dry weights comparable to that which developed in the standard medium. The following were very poor sulfur sources yet supported more growth than did the standard medium minus methionine: sodium sulfide, sodium thiosulfate, and thiourea. The ability of the other sulfur sources to support growth was questionable: potassium persulfate, sodium bisulfite, sodium dithionate, sodium hydrosulfite, sodium sulfate, sodium sulfite, and sodium thiocyanate.

The standard medium contained only two nitrogen sources: sodium glutamate and methionine. Sodium glutamate served as a carbon source as well as a nitrogen source, but methionine could serve only as a source of sulfur.