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Fungi straddle the realms of microbiology and macrobiology.  
The only above-ground signs of the humongous fungus are patches of dead trees and the mushrooms that form at the base of infected trees. Courtesy of the USDA Forest Service. The only above-ground signs of the humongous fungus are patches of dead trees and the mushrooms that form at the base of infected trees. Courtesy of the USDA Forest Service. It started out 2,400 years ago as a single spore invisible to the naked eye, then grew to gargantuan proportions by intertwining threads of cells called hyphae. Under a microscope, hyphae look like a tangled mass of threads or tiny plant roots. This tangled mass is called the fungal mycelium, and is the part of the famous honey mushroom that spreads for miles underground. If mushrooms and other fungi can get so huge, why mention them on a site about microorganisms? Visible fungi such as mushrooms are multicellular entities, but their cells are closely connected in a way unlike that of other multicellular organisms. Plant and animal cells are entirely separated from one another by cell walls (in plants) and cell membranes (in animals). The dividers between fungal cells, however, often have openings that allow proteins, fluids and even nuclei to flow from one cell to another. A few fungal species have no cell dividers: just a long, continuous cell dotted by multiple nuclei spread throughout. 
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This illustration shows the multicellular nature of mushrooms, and how they spread throughout the forest floor. © Bert Dodson.
The zoospores have no cell wall, are uniflagellated, and may swim for 24 hours on endogenous energy reserves. On contact with a suitable surface (e.g., a nematode cuticle), the zoospore encysts by withdrawing its flagellum and surrounding itself with a thick cell wall and then adhering to the surface.
Courtesy of MicrobeLibrary.org.
The fungi Arthrobotrys oligospora can capture a nematode when it merely touches the outside of its trap.
Courtesy of MicrobeLibrary.org.
Animation (Low Resolution, 256K QT)
Fungi are eukaryotic (you-carry-ah-tick) organisms—their DNA is enclosed in a nucleus. Many of them may look plant-like, but fungi do not make their own food from sunlight like plants do.
Yeast cell (blue highlights scars where buds formed)
Microbiol. Rev. 54:381-431, 1990
Some fungi are quite useful to us. We've tapped several kinds to make antibiotics to fight bacterial infections. These antibiotics are based on natural compounds the fungi produce to compete against bacteria for nutrients and space. We use Saccharomyces cerevisiae (sack-air-oh-my-seas sair-uh-vis-ee-ay), aka baker's yeast, to make bread rise and to brew beer. Fungi break down dead plants and animals and keep the world tidier. We're exploring ways to use natural fungal enemies of insect pests to get rid of these bugs.
Many more interesting facts about fungi can be found throughout the Microbe website, so keep clicking and reading.
You can also get a lot of details about fungi and see some cool images at The Microbial World website.
The fruiting body of the fungus Pilobolus. This specimen was found in cow dung.When the spore caps at the end of spore stalks fully mature, they burst. The spores may simply drop in the same area, or be carried by the wind or rain to new spots.
Courtesy of MicrobeLibrary.org.
Fungal hyphae
Courtesy of Alex Hausler, Givaudan Roure
When you hear the word fungus, you probably think of mushrooms. Did you know bread mold is a kind of fungus, too? And that the itchy burning of athlete's foot is, yes, caused by another fungus? And that when you take penicillin, you're taking a medicine made by a fungus?
Fungi come in a variety of shapes and sizes and different types. They can range from individual cells to enormous chains of cells that can stretch for miles.
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