Fungal Biology Lecture 4A (F09)

Lecture: Fungal Structure, Part C BIOL 4848/6948 - Fall 2009

Biology of Fungi Spore Germination

 Some general features  Some spores have a fixed point of Fungal Growth and germination termed the germ pore  Other spores swell (non-polar growth) prior Development to a germ-tube emergence from a localized point; subsequent wall growth is focused at this point

Spore Germination (cont.) Spore Germination (cont.)

1 Lecture: Fungal Structure, Part C BIOL 4848/6948 - Fall 2009

Spore Germination (cont.) Spore Germination (cont.)

 Some germinating spores exhibit  Hyphal tips show tropism to a variety of different types of tropism, i.e., a substances directional growth response to an  Nutrients external stimulus, e.g.,  Cysteine and other amino acids  Negative autotropism - germ tubes emerge  Volatile metabolites from a point on the spore furthest away  Sex pheromones from a touching spore  Positive tropism - germination towards an external stimulus

Mold-Yeast Dimorphism Mold-Yeast Dimorphism (cont.)

 Some fungi have the ability to alternate  Dimorphism occurs in response to between a mold form and a that of a environmental factors, of which no one yeast form - dimorphic fungi common factor regulates the morphological switch in all dimorphic  Several pathogens of humans exhibit fungi [Table 5.1, Deacon] dimorphism  e.g., Histoplasma capsulatum - mold at  Candida albicans 25°C, yeast at 37°C  Histoplasma capsulatum  e.g., Mucor rouxii - mold with oxygen, yeast in the absence of oxygen

Mold-Yeast Dimorphism (cont.) Mold-Yeast Dimorphism (cont.)

 What is clear is that there is a change in  Two fundamental questions on the polarity in terms of growth, thereby observed differences: making study of the cell cycle a  Are the differences the cause of significant focal point dimorphism?  To help identify the control of dimorphic  Did the dimorphic switch cause the growth, the mold and yeast phases of a differences? fungus are compared - typically differences in biochemistry, physiology, and gene expression are noted

2 Lecture: Fungal Structure, Part C BIOL 4848/6948 - Fall 2009

Mold-Yeast Dimorphism (cont.) Mold-Yeast Dimorphism (cont.)

 Examples of differences:  Cellular signaling and regulatory factors  Cell wall composition  Calcium, calcium-binding proteins, cAMP, pH, and protein phosphorylation have all been Organism Mold Phase Yeast Phase shown to fluctuate depending upon the growth Mucor rouxii More mannose form of a dimorphic fungus Paracoccidioides brasiliensis More -1,3- glucan More -1,3-glucan  Not clear is some or all or any directly impact Candida albicans More chitin the changes in cell morphology Histoplasma capsulatum More chitin  Gene expression differences Blastomyces dermatitidis More chitin  Measurement of mRNA production

 Again, no clear cut answer as to an obligatory role of a gene in dimorphism

Asexual Reproduction Asexual Reproduction (cont.)

 Two fundamentally  Sporangiospores different processes  Formed by the lead to the cleavage of development of two protoplasm within distinct types of a multinucleate mitospores: sporangium  Sporangiospores Sporangiospores (arrows) of Rhizopus. Source: Sporangium of Rhizopus and conidia of Penicillium. www.apsnet.org/education/IllustratedGlossary/  Conidia Sources: darwin.baruch.cuny.edu/bio1003/fungi.html and PhotosS-V/sporangiospore.htm www.visualsunlimited.com/browse/vu307/vu307719.html