I. Penicillium
The genus Penicillium is host to a wide variety of species found in practically all environmental niches. They have been given the name "green mold" or "blue mold", but many Penicillium species possess a variety of colors, textures, and morphological characteristics. The genus gained notoriety after their ability to produce antibiotics, namely penicillin, was discovered in 1941. Since then, bacteriologists, pharmacologists, chemists, and molecular biologists have pursued the study of Penicillium species as biochemical and industrial workhorses involved in the degradation of man-made chemicals, production of organic chemicals, and production of cheese.
Classification in Penicillium is based solely upon conidiophore structure called the penicillus. The penicillus, or "brush", is the whorled structure which bears the single celled conidia. The genus Penicillium can be divided into four groups based on the penicillus structure. These are the Monoverticillata, Asymmetrica, Biverticillata-Symmetrica, and Polyverticillata. Descriptions and illustrations of these are attached.
Today you will examine some Penicillium species and will write a key that can be used to identify the different species based on what you observe. A person interested in finding the species of an unknown should be able to use your key. You can devise your key based on colony morphology on the agar plate (be sure to specify the media), spore texture, other mycelial structures, etc... A copy of this should be submitted today and will be used for your final.
II. Aspergillus In 1792, Micheli was the first to distinguish the stalks and spore heads of Aspergillus. Under the microscope, he noted that the spore chains radiated from the central structure similar to an aspergillum, a religious item used in church services. Being a priest, he named the fungus Aspergillus.
The study of Aspergillus did not gain notoriety until the 1940's when their potetial as industrial and pharmaceutical powerhouses was being established. Presently, Aspergillus species are used to manipulate chemicals which are difficult to synthesize inorganically, to produce many organic acids for food industries, and are also used in the decomposition of man-made chemicals.
As with the genus Penicillium, Aspergillus is classified based on the morphology of the conidiophore. The conidiophores are borne on a hyphal cell termed a foot cell. The conidiophore stalk ends with an enlarged vesicle which bears a group of sterigmata. These, in turn, can bear secondary sterigmata called metulae which then bear the conidia in unbranched chains.
Primary classification of Aspergillus is based upon the number of series of sterigmata which can be uniserate, uni- and biserate, and biserate only. Further classification is based upon the presence or absence of hulle cells (thick walled cells similar to chylamydospores), and also upon the characteristics and pigmentation of conidiophores.
For this part of the lab, you will examine different species of Aspergillus. An incomplete key is given where the distinguishing characteristics of particular species are listed. Your job is to complete the key by writing down the species name in the blank that follows after the description.
III. Nematophagous fungi
Included in the abundant and diverse microbial population of soil are fungi that are taxonomically distinct but are ecologically a natural group; they are united by their adaptation to a predacious habit. These remarkable organisms are able to capture, kill, and consume microscopic animals which include amoebae, nematodes, rotifers, and isects. we will focus today on the nematophagous fungi, namely Arthrobotrys conoides.
There are approximately 150 species of nematophagous fungi. Some of these belong to the phyla Chytridiomycota, Oomycota, Zygomycota; but many belong to the form-phylum Deuteromycota, form-order Moniliales. The structures produced by these fungi for the capture of their prey vary greatly in design and detail, but they all trap nematodes by either adhesion or occlusion.
Arthrobotrys is characterized by tall, colorless conidiophores bearing conidia at the tip and often at several swollen points below. The conidia are colorless, 2 to 3 celled, and leave a conspicuous scar when released. The fungus forms constricting rings or sticky networks of loops to trap its prey.
Obtain a plate of Arthrobotrys. Pipet some nematodes from the nematode plate onto the fungal culture. Observe under the dissecting scope and locate a trapped nematode.Prepare a wet mount of the trapped nematode and fungal structures and observe under the microscope. Record your observations.