The Occurrence of Arachniotus Citrinus in Soils

Abstract

Arachniotus citrinus was first described by Massee and Salmon in 1902 (3). This member of the family Gymnoascaceae was observed growing on kangaroo dung collected in the London Zoo. Morphological studies were made on the gross specimen only, as cultivation of the fungus on synthetic media was not attempted. Since that date no fur? ther observations of this ascomycete have been reported. Recently, while a large number of Tennessee soil samples were being screened for the presence of Histoplasma capsulatum and Microsporum gypseum, two soil samples yielded A. citrinus. One isolate was recov? ered indirectly from soil by passage through mice (2), while the second was observed developing adventitiously on strands of sterilized human hair used as bait for isolation of M. gypseum (1). A. citrinus grew readily on Sabouraud dextrose agar, forming a white cottony colony which slowly turned lemon-yellow 3 in color as asci and ascospores were developed. On Czapek's agar mycelial development was sparse but numerous lemon-yellow clusters of asci were formed. There was scant production of mycelium on sterilized rabbit dung pellets and rabbit dung extract agar (Fig. 1A). However, this medium was excellent for inducing ascus formation. Microscopic examination of the fungus grown on all these media revealed essentially similar findings. It was noted that copulation branches arose from mycelial filaments and coiled about each other (Fig. 1B). From these copulation branches asci were successively developed (Fig. 1C). This successive development of asci from the copulation branches led to the formation of clusters of asci along the hyphae (Fig. ID). No signs of a peridium were found. Each ascus enclosed eight elliptical, smooth, lemon-yellow spores (Fig. ID). When mounted in