Wednesday, November 27, 2013

Some Fungi You Should Be Thankful For

Ahem... For which you should be thankful.

Here at the PDIC we focus on the negative impacts of fungi, bacteria, nematodes, and viruses on plant health and human well-being. This tends to overshadow the fact that they do more good than harm in the grand scheme of things. Since we deal mostly with fungi, I offer several for which we should be grateful.

Saccharomyces cerevisiae helping in the kitchen.
Saccharomyces cerevisiae. The lowly baker's yeast is one of humanity's best friends in the fungal kingdom. It's a one-celled organism, whereas most fungi grow as thread-like "hyphae". More importantly, it's capable of fermentation, a process that starts with carbohydrates such as sugar and results in energy for the fungus and alcohol and carbon dioxide as byproducts. Without the yeasts, the rolls and stuffing on the Thanksgiving table would be unleavened, and there simply would be no wine, beer, or spirits at the celebration.

Mycorrhizal fungi at work, under the surface.
Plant Pathology Department Slide Collection
Mycorrhizae. When we look at a plant, we don't usually think about the roots. Even when we do think about roots, we usually forget that most plants partner-up with certain fungi that enable them to better extract nutrients from soil. This association is known scientifically as a "mycorrhiza" (plural "mycorrhizae"), which is simply Greek for "fungus-root". Other benefits have been ascribed to this relationship such as increased resistance to root diseases and other stresses. There are two basic groups: the ectomycorrhizae and the arbuscular mycorrhizae. The former are characteristically associated with trees and form a fungal mantle on the outside of the root, slightly modifying its structure and appearance. Often these fungi produce mushrooms or puffballs (above or below ground) when it comes time to reproduce. A good example is the small, reddish Russula mushroom we see popping up each fall in our area. The arbuscular mycorrhizae form on both herbaceous and woody plants, and are very inconspicuous. If you aren't a scientist dedicated to plant roots in some way or another, you probably won't ever notice them. Do appreciate them, though, as they are close collaborators with the plants we so value and need.

Brown cubical rot of pine wood, caused by the fungus Meruliporia incrassata.
Plant Pathology Department Slide Collection
Wood decay fungi. Yes, wood decay fungi are unwelcome when they invade living trees or our homes, but we’d be in deep trouble without them. They are a critical cog in the carbon cycle, degrading the cellulose and lignin components of wood. In fact, fungi are the only organisms in the world that produce the enzymes necessary to break down lignin. Without them we would be up to our eyeballs in woody debris. There are a number of spin-off benefits, as well. For example, pulping using these fungi will be better than current processes in terms of reducing both energy use and chemical waste.

Fungi with medicinal applications. We remember with gratitude the mold Penicillium, which brought about the antibiotic revolution. Apart from the penicillins, the cephalosporin antibiotics can also be traced to a fungal metabolite. The cholesterol-lowering drugs compactin and lovastatin are derived from fungal fermentation, although other statin drugs are synthetic or semi-synthetic. Traditional Chinese medicine makes use of a number of different fungi, some of which may find their way into the western pharmacopeia.

Agriculturally important fungi. Several fungi such as Beauveria bassiana and Metarhizium anisopliae are used as biological insecticides. Some such as Trichoderma harzianum are found in biological fungicides. Also, an important group of chemical fungicides, the strobilurins, were developed based on a chemical found in the mushroom Strobilurus tenacellus.

Farmed, or Farmer?
Neocallimastix and company. Probably the most obscure group on the list, it was only within the last forty years that these were recognized as fungi and not protozoans. This includes genera with such names as Orpinomyces, Piromyces, and Neocallimastix, Once known as the "rumen chitrids", they are better called "anaerobic gut fungi", "anaerobic zoosporic fungi", or simply "anaerobic fungi". They work together with bacteria and protozoans in the digestive systems of many kinds of herbivores to break down the fibrous diet of these animals. They are found in the rumen of animals such as sheep and cattle, but have also been found in deer, horses, kangaroos, even rhinos and elephants. They do a better job than bacteria at breaking down lignocelluloses, and their rhizoids can get through plant cuticles, which bacteria & protozoans cannot penetrate. We really should be thinking of cows as farmers, responsible for a large and diverse population of microbes that convert roughage into materials that the cows can metabolize.

Strawberry jelly ingredients. Where does the citric acid come from?
Agaricus bisporus and other edible fungi. These are probably what you first think of when you consider "good" fungi, though their contributions pale in comparison to the others listed above. Note that the portabella and crimini represent a strain of Agaricus bisporus, the same white button mushroom of pizza fame. Of course there are many other wonderful edible fungi out there. A number are more popular in oriental culture than in the west, but you've probably eaten Auricularia in oriental soups. You may not be aware, though, of your consumption of a product that is commercially produced using the mold fungus Aspergillus niger: citric acid. The next time you see "citric acid" on the label, think fungus rather than lemons! And whatever you eat, have a Happy Thanksgiving!

Read on to find out about Insects to Be Thankful For.