Ultrastructural studies of induced morphogenesis byAspergillus parasiticus

Abstract

Vegetative development of Aspergillus parasiticus may follow two patterns of morphogenesis depending upon the presence or absence of manganese ions in the medium. This alteration of morphology is suggestive of a hyphal-yeastlike dimorphism. Aspects of this morphogenesis of A. parasiticus are illustrated and described. Anomalies of the fine structural appearance of the cell wall of hydrated conidia following inoculation into a manganese-deficient synthetic medium occurred prior to germ tube formation. After approximately 96 h incubation, ceils of A. parasiticus underwent alteration to thick-walled, slightly elongate forms resembling arthrospores. These altered forms had scanty cytoplasm and 3 distinct cell wall layers. The thick inner layer had multiple, slightly undulating parallel boundaries perhaps resulting from the repeated deposition of newly synthesized cell wall material. Along these boundaries, small areas of electron-dense material were associated with delicate membrane-like microstructures suggestive of bilayer leaflets. Ultrastructurally, these altered forms of A. parasiticus do not resemble closely those reported previously for the yeastlike phases of certain of those fungi exhibiting true hyphal-yeastlike dimorphism.Aspergillusparasiticus Speare is of interest because of its ability to produce aflatoxin B1, a potent hepatocarcinogen (Wogan, 1969). In a study of the biosynthesis of aflatoxin B1, Detroy & Ceigler (1971) observed that vegetative development of A. parasiticus may follow 2 patterns of morphogenesis depending upon the presence or absence of manganese ions in the culture medium. When conidia ofA. parasiticus were inoculated into complex media containing yeast extract, the fungus grew in its normal hyphal form. When cultured in a manganese-deficient synthetic medium, it grew as large spherical, "yeastlike" structures which appeared to be a stable, morphogenetic form. Upon subsequent transfer of the "yeastlike" forms to synthetic medium containing manganese, further growth produced filamentous hyphal cells. These 2 patterns of morphogenesis suggested a hyphal-yeastlike dimorphism as characterized by certain of the important fungal pathogens of man and animals.It is the purpose of this study to describe the fine structure of the 2 vegetative forms of A. parasiticus, and to examine certain aspects of ultrastructural reorganization occurring during the culturally induced morphogenesis as characterized by this fungal organism. MATERIALS AND METHODSStock cultures of A. parasiticus ATCC 15517 were maintained on potato dextrose agar (Difco) slants at 30°C. Conidia were harvested from 5-day old slant cultures by flooding them with sterile deionized water and gently dislodging the conidia with an inoculating loop. The conidial suspensions were washed several times by centrifugation with sterile deionized water. Five ml samples of a heavy suspension of washed conidia were inoculated into 50 ml vol of the synthetic medium described by Detroy & Ciegler 179 Med Mycol Downloaded from informahealthcare.com...

Manganese Deficiency Is Required for High Itaconic Acid Production From D-Xylose in Aspergillus terreus

“…A deficiency in manganese ions is known to change the morphology of Aspergillus spp. from smoothly filamentous to stubbed, swollen, highly branched and even yeast-like hyphae (Barnett and Lilly, 1966; Garrison and Boyd, 1974; Kisser et al, 1980; Papagianni, 2006; Clark et al, 2016). In agreement with this, the morphology of A. terreus at Mn 2+ concentration <3 μg L –1 was mostly represented by yeast-like forms and loose cell clumps, and formation of hyphae occurred only over 5 μg L –1 (Figure 3).…”