Introduction
Phycomyces blakesleeanus is a filamentous fungus that belongs to the order Mucorales, class Zygomycetes. Phycomyces is very sensitive to light and most Phycomyces research has been directed to investigate various aspects of the photobiology of Phycomyces. In fact it was its sensitivity and graded photoresponses that stimulated Max Delbrück to investigate the phototropism of Phycomyces macrophores. Others aspects of the biology of Phycomyces have been investigated in depth, like spore germination, carotene biosynthesis and sexual development. Metabolic, developmental, and photoresponse mutants have been isolated and some of them have been mapped in the Phycomyces genetic map. Most research and genetic analysis have been carried out with the standard wild type strain NRRL1555, and the information contained in this site will refer almost exclusively to it.
This site has been created with the aim of providing information for the general public with interest in the biology of Phycomyces and to provide an electronic forum for the rapid exchange of ideas and new experimental results for the scientists involved in Phycomyces research. Those interested in more details of the biology of Phycomyces should read the two major reviews: Bergman, K. et al. (1969) Phycomyces. Bacteriol. Rev. 33, 99-157; Cerdá-Olmedo E. and Lipson E. D. (eds.) (1987) Phycomyces. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, USA. Many of the pictures that appear in this site have been taken from the Phycomyces book.
Phycomyces reviews:
Phycomyces
life cycle
Phycomyces starts its vegetative life cycle as a spore, with three nuclei in average, that germinates after a heat-shock or after exposure to certain chemicals in the presence of suitable nutrients. After activation, the spore will swell and will produce one, two, or sometimes three germination tubes. The germination tubes will grow at their tips, branching repeatedly to form lateral tubes. The resulting tubes, hyphae, will form a thread-like structure, the mycelium that will grow until it occupies the available medium. Phycomyces hyphae contain no transverse walls (septa), and thus the whole mycelium can be considered as a a single cell (coenocyte). Vegetative reproduction starts with the development of sporangiophores, specialized unbranched hyphae that grow vertically. The nuclei in the hyphae will migrate through the developing sporangiophore and will be packed into spores inside a sporangium, a sphere that is formed at the tip of the sporangiophore. The spores can be liberated from the sporangium and will germinate to create a new mycelium. There are two types of sporangiophores of very different size, macrophores and microphores. Macrophores can grow for several cm and their growth is very sensitive to external stimuli such as light, wind, barriers, and the presence of nearby objects. The phototropism of the macrophores has been investigated in great detail. Microphores, on the contrary, are about 1 mm long. The number of macro- and microphores that grow in a culture depends on the ambient light: blue light stimulates macrophorogenesis and inhibits microphorogenesis.
There are two sexes in Phycomyces, (+) and (-), with no morphological difference. When hyphae of the two sexes grow close to each other they will slow their growth and will swell, grow, and brach to become zygophores, the first differentiated structures of the sexual cycle. Zygophores have protusions in all directions and a bright colour due to abundant carotene synthesis. Zygophores of opposite sex come into contact to become progamentangia that grow out of the aqueous medium and into the air, as their protusions proliferate and interwine. A gamentangium becomes delimited at the tip of each progamentangium by a transverse septum. The remaining parts of the progametangia are called suspensors, since they support the gamentangia in the air. Thorn-like appendages grow out of the suspensor wall and the two gamentangia mix their contents to form the zygospore. The zygospore remain dormant for months until a germsporangiophore emerges forming a germsporangium containing about 10,000 germspores, similar to the vegetative spores, that are the product of karyogamy and meiosis. The germspores, when placed in appropiate medium, will germinate to form a vegetative mycelium.
You can make a tour through the
vegetative cycle of Phycomyces.
First step in the life cycle: the spore
Click in the figure for more information and photographs from relevant stages of the Phycomyces life cycle.
main
page - life cycle - genome - photoresponses - methods - abstracts - directory - Delbrück - web sites