Studies on Pythiopsis cymosa from Newfoundland

Abstract

An isolate of Pythiopsis cymosa de Bary was obtained from a pupa of the blackfly Prosimulium fuscum (Syme & Davies). The optimum temperature for growth of the isolate was 17°C. The isolate was highly aerobic and grew best at pH 6·9 on a medium containing 4 g of casamino acids per litre. Glucose utilization was first detected at the end of the lag phase, and 79% of the total glucose supplied was utilized during the 24 h period following the end of the lag phase. Ninhydrin-positive substances supplied by casamino acids were utilized except cysteic acid and urea. Compounds released by the fungus into the medium were: γ -aminobutyric acid, citrulline, α -aminoadipic acid, carnosine, α -amino- n -butyric acid, β -alanine and glutamine or asparagine (or both). The morphology of the isolate is described. An attempt to infect a mixed blackfly larval population in the laboratory by using fungal cysts failed.