Physiological Studies on an Isolate ofSaprolegnia Feraxfrom the Larval Gut of the BlackflySimulium Vittatum

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Abstract
An isolate of Saprolegnia ferax was obtained from the gut of a larva of the blackfly Simulium vittatum. Growth occurred best over a broad temperature optimum of 19 C through 26 C. The isolate was aerobic and grew best at pH 5.6. In media containing glucose (5 g/liter), the optimum concentration of vitamin-free casamino acids and lactalbumin hydrolysate was 4 g and 8 g per liter, respectively. Any effect of various pH indicators on dry weight yield was not detected; however, pH indicators were not incorporated into final media because all indicators tested, except for bromophenol blue, were taken up by the fungus. The optimum concentration of phosphate was 10 mM. The pattern of utilization of ninhydrin-positive substances from vitamin-free casamino acids and from lactalbumin hydrolysate, with and without added glucose, was determined. In the presence of lactalbumin hydrolysate, but without added glucose, aspartic acid, threonine, serine, glutamine and/or asparagine, alanine, isoleucine, leucine, tyrosine, and phenylalanine were utilized more rapidly than when glucose was present. Also, ammonia was released into the medium at a greater rate in the absence of glucose. The release of the polyamine spermidine was detected during lysis when the isolate was grown on vitamine-free casamino acids. The polyamines spermine and spermidine were detected during lysis after growth on lactalbumin hydrolysate.