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You may notice the endnotes don't necessarily start at "1".  The following article is an excerpt from a back issue of our on-line newsletter.



Microscopic Examination of Common Fungi

When hunting for interesting life-forms to study with the microscope, one's own refrigerator can be a productive search area.  Bacteria, molds, and yeasts are present in even the best-kept refrigerators, but the most rewarding search is one carried out in a fridge that hasn't been cleaned in a couple of months.

Penicillium (?) growth on a carrot
This un-appetizing mold growth on a carrot gives us an abundant source of hyphae, conidiophores, etc. to study with the microscope. It appears the mold infestation started in a bruised or torn section in the side of the carrot.  Opportunistic fungi-- including Penicillium spp.-- can also invade damaged tissues in animals and people.   Zygomycosis, a rare but dreadful disease, comes to mind.
Procedure:  A search in the refrigerator turned up at least one piece of moldy produce:  a carrot showing tufted masses of white and blue-green fungi.  Samples of this were removed with forceps 5 and placed on a clean microscope slide; two or three drops of prepared hematoxylin stain were then added and allowed to soak into the mold samples.  A clean cover slip was placed on the preparation and as many air bubbles as possible were pressed out gently. The slide was studied with an Observer III microscope and photographs were taken using a MiniVID USB eyepiece camera (an early version of the camera with lower resolution).

Results and Discussion:  At 40x total magnification, the stained fungi showed up as tangled masses of thin stalks (hyphae), sometimes terminating in complex structures that warranted closer inspection. At 100x total magnification these structures became much clearer and were vaguely reminiscent of sea-anemone tentacles or squashed flowers. The first MiniVID photo was taken at 100x.
Penicillium (?) mold at 100x
At 400x total magnification, individual spherical structures (conidia) became visible; these are shown in the photographs below. The "flower-like" conidiophore was difficult to bring into focus, thanks partially to its high 3-dimensional relief as compared to the rest of the hyphae.
Penicillium (?) conidiophore at 400x
Though the hematoxylin stain was chosen arbitrarily (without researching what the best stain would have been), it adhered well. A proper procedure would have included de-staining to remove excess pigment, but we obtained passable results for this mini-experiment. We initially guessed that the fungus samples from the carrot represented a common member or members of the genus Penicillium, or perhaps Cladosporium. Since no photo-atlas of fungi was handy, some meandering on the web turned up the very informative doctorfungus.org website. The site contains an impressive, searchable image bank.
Of the photos we searched, the closest match was Penicillium chrysogenum, a common fungus in many households-- and the original source of the antibiotic penicillin.  Though P. chrysogenum may not be the true identity of our sample (any mycologists out there: feel free to make suggestions), one can easily notice a similarity here.  Compare the "strings" of spherical phialides on the conidiophores of known P. chrysogenum with those in our unidentified mold sample, shown below  6:

Penicillium (?) conidiophores at 400x
It really looks like the fungus from which the drug penicillin was discovered.  See also Tom Volk's Fungus of the Month for November 2003;  it has a nice phase-contrast photo of P. chrysogenum.
The above photomicrographs were taken with the old version of the USB Mini-VID eyepiece camera, fitted into an Observer III student microscope.  The sample was prepared minimally and handled with very little care, and the slide was only a temporary mount.  Despite its highly improvised character, this mini-experiment has brought to light some interesting objects which had been silently growing in the refrigerator.

We hope you enjoyed this article!

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Notes:

5 Tearing off pieces of the fungus probably filled the air with spores. Now they're really everywhere. The writer probably inhaled some of them, which is likely not desirable.
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6 As you can see, the conidiophores, phialides, etc. are tangled and mashed all over the place in our samples, causing them not to look like the nice and neat reference photos with which we're comparing them. Also, there are so many genera and species of fungi that it might be a little na´ve for us to think we've pegged the identity this easily. It has been an enjoyable try, though.
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While the information in this newsletter is thought to be accurate to the best of the authors' current knowledge, it is not guaranteed to be free of errors or to be suitable for any particular use. The procedures and experiments outlined within can be dangerous or even fatal if carried out improperly. If you choose to attempt any of them, you proceed entirely at your own risk.

Contents of his newsletter are Copyright 2010.  Please email us if you find any errors or omissions or would simply like to make a suggestion.


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