As some of you know, currency or money can often carry very small particles on its surface. Through a number of studies it has been shown that anywhere from 75% to 97% of one dollar bills contain detectable amounts of cocaine! At first these numbers seem staggering, but further investigation has pinpointed the culprit of most of the contamination to ATM machines and other money counting devices. One bill that has been in contact with cocaine can contaminate hundreds of other bills it touches in an ATM machine.

     Besides cocaine, dollar bills can carry many other things that are undectable with the naked eye or even a microscope. Some fungi, mainly molds, produce reproductive spores at a prolific pace. In fact, right now you are likely breathing in hundreds of spores with every breath! Fungal spores are everywhere, and some can take residence on things that people use everyday, like money! This petri dish on the right contains media selective for fungi and was inoculated with one swipe of the dollar bill over the surface. As you can see, many different fungal spores germinated on this petri dish.

     Well not exactly, mushroom forming fungi are members of the Basidiomycota and Ascomycota. Molds are classified in the deuteromycetes, or the Fungi Imperfecti. The deuteromycetes have no known sexual (teleomorph) state and usually reproduce asexually (anamorph) by conidia. Because they have no known sexual (teleomorph) state, they cannot be placed with complete confidence in any of the phyla. About 90% of the deuteromycetes are thought to have affinities to the Ascomycota because they both reproduce asexually by conidia. It is likely that these fungi have no sexual state at all, the prolific asexual state is adequate for evolution and survival. Some of these deuteromycetes are common soil saprophytes, which is necessary for decomposition and nutrient recycling. Aspergillus, Penicillium, and Trichoderma are some of the deuteromycetes that are very common as well as have important industrial applications. Aspergillus niger is used on an industrial scale to produce millions of gallons of citric acid which is a common ingredient in a lot of foods including soft drinks. Penicillium chrysogenum is used to make thousands of gallons of Penicillin. Trichoderma not only is used to make stone washed jeans but also has potential as a biocontrol agent.

     Members of the deuteromycetes can also be harmful to humans. Some of these fungi can cause plant diseases, like Verticillium that can cause a vascular wilt in trees. There are also some species of the more common genera, Aspergillus and Penicillium, that can cause mycoses in immunocomprimised people. Aspergillosis is known as the most feared of all human fungal diseases. It is usually a pulmonary infection that is characterized by the presence of highly septate, hightly branched hyphal structures. This gives the overall appearance of an "army on the march." Deuteromycetes don't have to grow inside your body for them to negatively affect you. Stachybotrys chartarum, the black mold that allegedly causes sick building syndrome, can grow in moist places in your house. The conidia and spores of this mold are thought to cause problems to humans when inhaled. However, no study has proven that Stachybotrys is the causative agent of sick building syndrome, so don't burn your house down quite yet.

     The animation on the left is 6 coins of varying denomination that were streaked onto Potato Dextrose Agar and allowed to grow. As you can see, the plates are colonized rather quickly. All of this growth occured after only 5 days! Remember that when a spore lands on a suitable substrate, it germinates and then grows out in every direction. This is why colonies usually appear to be round in shape. The deuteromycetes are notoriously hard to identify to species. Genera are separated by the differences in their conidiogenous cells or conidia, colony color, hyphal structure, pigmentation of media, and consistency and topography of the colony. If you put these characteristics together you will get a synoptic key that should lead to the accurate identification of a sample. Remember that you only get an accurate I.D., when the characteristics are accurately interpreted. Not to mention that there are approximately 1,680 genera and 17,000 species classified in this group!

OK, So Where Do I Start?

     Let's focus on the petri dish in the upper left hand corner of the animation. With a lot of practice you might be able to identify one of these molds by just looking at the colonies, but I'm not that good so we will have to do some more work. A tape mount is a quick and easy way to look at the hyphae and conidiation of a colony. You will need 1) Clear Tape, 2) Microscope Slide, 3) Water, and a 4) Microscope. You then lay the tape, sticky side down, on the colony and pick up some of the hyphae and conidia. The tape is then placed over a drop of water onto the slide, so the tape acts as your coverslip. The slide can then be viewed under the microscope up to 1000x (oil immersion). After making a tape mount of this colony, this is what can be seen under the microscope...

     The colony that I looked at turns out to be a species of Cladosporium. Cladosporium spp. are common deuteromycetes that can be isolated indoors or outdoors. Cladosporium, along with Aspergillus, Penicillium, and Trichoderma are the most common "airborne" members of the deuteromycetes. They are grouped in the dematiaceous or darkly pigmented molds which means that the colony is dark green to black in color. There are about 30 species in the genus Cladosporium and the species distinctions are difficult like most of the deuteromycetes.

If you have anything to add, or if you have corrections, comments, or recommendations for future FotM's (or maybe you'd like to be co-author of a FotM?), please write to me at volk.thom@uwlax.edu

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