Fungal spores are smaller and lighter than plant seeds, but they are not usually released as high in the air. The giant puffball mushroom bursts open and releases trillions of spores: The huge number of spores released increases the likelihood of spores landing in an environment that will support growth [Figure 4].
Like animals, fungi are heterotrophs: They use complex organic compounds as a source of carbon rather than fixing carbon dioxide from the atmosphere, as some bacteria and most plants do.
In addition, fungi do not fix nitrogen from the atmosphere. Like animals, they must obtain it from their diet. However, unlike most animals that ingest food and then digest it internally in specialized organs, fungi perform these steps in the reverse order. Digestion precedes ingestion. First, exoenzymes, enzymes that catalyze reactions on compounds outside of the cell, are transported out of the hyphae where they break down nutrients in the environment.
Then, the smaller molecules produced by the external digestion are absorbed through the large surface areas of the mycelium. As with animal cells, the fungal storage polysaccharide is glycogen rather than starch, as found in plants. Fungi are mostly saprobes, organisms that derive nutrients from decaying organic matter. They obtain their nutrients from dead or decomposing organic matter, mainly plant material. Fungal exoenzymes are able to break down insoluble polysaccharides, such as the cellulose and lignin of dead wood, into readily absorbable glucose molecules.
Decomposers are important components of ecosystems, because they return nutrients locked in dead bodies to a form that is usable for other organisms. This role is discussed in more detail later. Because of their varied metabolic pathways, fungi fulfill an important ecological role and are being investigated as potential tools in bioremediation. For example, some species of fungi can be used to break down diesel oil and polycyclic aromatic hydrocarbons.
Other species take up heavy metals such as cadmium and lead. The kingdom Fungi contains four major divisions that were established according to their mode of sexual reproduction. Polyphyletic, unrelated fungi that reproduce without a sexual cycle, are placed for convenience in a fifth division, and a sixth major fungal group that does not fit well with any of the previous five has recently been described.
Not all mycologists agree with this scheme. Rapid advances in molecular biology and the sequencing of 18S rRNA a component of ribosomes continue to reveal new and different relationships between the various categories of fungi. The traditional divisions of Fungi are the Chytridiomycota chytrids , the Zygomycota conjugated fungi , the Ascomycota sac fungi , and the Basidiomycota club fungi.
An older classification scheme grouped fungi that strictly use asexual reproduction into Deuteromycota, a group that is no longer in use.
The Glomeromycota belong to a newly described group [Figure 5]. Many fungi have negative impacts on other species, including humans and the organisms they depend on for food. Fungi may be parasites, pathogens, and, in a very few cases, predators.
The production of enough good-quality crops is essential to our existence. Plant diseases have ruined crops, bringing widespread famine. Most plant pathogens are fungi that cause tissue decay and eventual death of the host [Figure 6]. In addition to destroying plant tissue directly, some plant pathogens spoil crops by producing potent toxins. Fungi are also responsible for food spoilage and the rotting of stored crops. For example, the fungus Claviceps purpurea causes ergot, a disease of cereal crops especially of rye.
The most common signs and symptoms are convulsions, hallucination, gangrene, and loss of milk in cattle. The active ingredient of ergot is lysergic acid, which is a precursor of the drug LSD. Smuts, rusts, and powdery or downy mildew are other examples of common fungal pathogens that affect crops.
Aflatoxins are toxic and carcinogenic compounds released by fungi of the genus Aspergillus. Periodically, harvests of nuts and grains are tainted by aflatoxins, leading to massive recall of produce, sometimes ruining producers, and causing food shortages in developing countries. Fungi can affect animals, including humans, in several ways. Fungi attack animals directly by colonizing and destroying tissues.
Humans and other animals can be poisoned by eating toxic mushrooms or foods contaminated by fungi. In addition, individuals who display hypersensitivity to molds and spores develop strong and dangerous allergic reactions. Fungal infections are generally very difficult to treat because, unlike bacteria, fungi are eukaryotes.
Antibiotics only target prokaryotic cells, whereas compounds that kill fungi also adversely affect the eukaryotic animal host. They are usually visible on the skin of the animal. Fungi that cause the superficial mycoses of the epidermis, hair, and nails rarely spread to the underlying tissue [Figure 7]. These conditions are usually treated with over-the-counter topical creams and powders, and are easily cleared.
More persistent, superficial mycoses may require prescription oral medications. Systemic mycoses spread to internal organs, most commonly entering the body through the respiratory system. For example, coccidioidomycosis valley fever is commonly found in the southwestern United States, where the fungus resides in the dust.
Once inhaled, the spores develop in the lungs and cause signs and symptoms similar to those of tuberculosis. Histoplasmosis [Figure 7] c is caused by the dimorphic fungus Histoplasma capsulatum ; it causes pulmonary infections and, in rare cases, swelling of the membranes of the brain and spinal cord.
Treatment of many fungal diseases requires the use of antifungal medications that have serious side effects. Opportunistic mycoses are fungal infections that are either common in all environments or part of the normal biota. They affect mainly individuals who have a compromised immune system. Patients in the late stages of AIDS suffer from opportunistic mycoses, such as Pneumocystis , which can be life threatening. The yeast Candida spp. Fungi may even take on a predatory lifestyle.
In soil environments that are poor in nitrogen, some fungi resort to predation of nematodes small roundworms. Species of Arthrobotrys fungi have a number of mechanisms to trap nematodes.
For example, they have constricting rings within their network of hyphae. The rings swell when the nematode touches it and closes around the body of the nematode, thus trapping it. The fungus extends specialized hyphae that can penetrate the body of the worm and slowly digest the hapless prey.
Fungi play a crucial role in the balance of ecosystems. They colonize most habitats on Earth, preferring dark, moist conditions. They can thrive in seemingly hostile environments, such as the tundra, thanks to a most successful symbiosis with photosynthetic organisms, like lichens. Fungi are not obvious in the way that large animals or tall trees are.
Yet, like bacteria, they are major decomposers of nature. With their versatile metabolism, fungi break down organic matter that is insoluble and would not be recycled otherwise. Food webs would be incomplete without organisms that decompose organic matter and fungi are key participants in this process. Decomposition allows for cycling of nutrients such as carbon, nitrogen, and phosphorus back into the environment so they are available to living things, rather than being trapped in dead organisms.
Fungi are particularly important because they have evolved enzymes to break down cellulose and lignin, components of plant cell walls that few other organisms are able to digest, releasing their carbon content. Fungi are also involved in ecologically important coevolved symbioses, both mutually beneficial and pathogenic with organisms from the other kingdoms.
Mycorrhiza , a term combining the Greek roots myco meaning fungus and rhizo meaning root, refers to the association between vascular plant roots and their symbiotic fungi. Somewhere between 80—90 percent of all plant species have mycorrhizal partners. Wild yeast attracted to grain and flour mixture was responsible for making bread rise. With the development of more varieties of grains, baking leavened bread eventually became a skill, in Egypt, along with their ability to brew beer.
It was probably much later that the Egyptians learned that they could take part of the risen dough from one baking to the next. This was a revolutionary concept since bread making would no longer rely on the chance landing of yeast on the dough. In addition, this gave a more consistent quality to bread.
Relying on the chance landing of yeast on bread dough also invited unwanted bacteria and other fungi to infest the dough, often leading to bad taste in bread. Bread became a significant part of Egyptian life as evidenced by their use of bread for their money in trading for goods and their homage to Osiris, the god of grain.
Even the workers who built the pyramids were paid with bread. When leavened bread was first discovered and for thousands of years after, the reason as to why this type of bread was light and fluffy was not known.
As in many other unexplained phenomena, a supernatural explanation was given for its existence. In the case of the ancient Egyptians, it was said that the god Osiris observed that the journey from Earth, to the land of the dead, was a difficult one and decided to lighten their burden, by giving mankind the ability to make leavened bread, so that their travel could be made with a lighter load.
However, even today, some unleavened, commercial breads are made Figure 1. One reason that it is still made is for its consumption during the Seder, the ceremonial dinner that is held during the first two days of the Passover, celebrating the Exodus of the Hebrews from Egypt. The story goes that in their haste to leave Egypt, the Hebrews took the raw dough for bread on their journey and baked it in the hot desert sun into a hard unleavened cracker called matzoh because they did not have the time to allow the bread to rise.
The Passover refers to God "passing over" the houses of the Jews, as he was slaying the first borne of Egypt. The cultivation of grains and bread making eventually spread to Europe where many advances in bread making occurred. Rome, in B. It consist of two circular stones, one on on top of the other. Grain is admitted through the circular opening in the center of the top stone and turned with with a wooden handle being inserted into the slot on top. By B.
Because bran gave bread a dark appearance and had a laxative property about it and gave people gas, only peasants ate bread made from grains. This trend is something that has persisted in Europe and English speaking countries to this day even though we now know that eating white bread has its nutritional draw backs. The members of the first baker's guild, Collegium Pistorum , was unusual for its time. The bakers were the only Roman craftsmen who were freemen.
All other traders were conducted by slaves. However, there were also disadvantages. The bakers and their children were not allowed to withdraw from the guild to take up another trade. They also were not allowed to mix with comedians and gladiators or to attend performances at amphitheatres so as not to be influenced by the vices of the ordinary people. This guild, now called the Guild of Master Bakers, has survived to this day with its headquarters in England and with its own coat of arms Figure 3.
However, because of the preference for white and brown bread by A. The practice of taking a bit of risen dough, the leaven from a previous loaf of bread also continued for thousands of years, following its discovery in Egypt, and continued among the early settlers of North America. It became a custom to give daughters a bit of leaven, to take with her when she got married. In this matter, yeast in risen dough, have been passed on for many generations.
Even today, there are still families that have retained this practice and have leaven that can be traced back in their families for over years.
Leavens that were passed on also differed in quality. Gold prospectors during the 19th. The sour dough bread that resulted from this type of leaven has become one of the most popular of breads. In San Francisco, the sourdough center of the world, one of the famous bakeries claims to have a sourdough starter that is over years old. Some superstitions also became associate with bread. In ancient Palestine, it was customary not only to throw all leaven out of a home where someone had died, but all the leaven in neighboring houses, as well, because it was thought that the angel of death had thrust his sword into the leaven.
Folklore concerning yeast have come about even in more recent time. In the United States, there is the story of how the Fleischmann brothers of Austria visited the United States in to attend their sister's wedding.
However, they were less than thrilled about the flavor of the bread served to them. Two years later, when they emigrated to America, they decided to take a yeast sample with them because they were concerned about the lack of good yeast in America.
The leaven of that yeast culture went on to become the basis of their yeast business, Fleischmann's Yeast, that still exist today.
While the use of leaven was important in ensuring that baked bread would rise, it was not very convenient. After the discovery that yeast was the leavening agent responsible for making bread rise, a practical means of obtaining yeast for the purpose of baking bread was developed that did not require saving the leaven from previous loaves.
This was the yeast cake , which could be stored for long periods of time and had the added advantage of being able to buy specific strains of yeast for baking different types of bread. The production of yeast cake is a simple process, which involves the removal of water from yeast cells, which suspends their metabolism, making possible the long term storage of yeast. Today, the use of dried yeast is more commonly used in baking bread in homes. In approximately years since leavened bread has been baked, bread has remained essentially the same.
Grinding the grain into flour, mixing it with water and other ingredients, depending on what kind of bread you are making, forming the dough into loaves, allowing them to rise and then baking them in an oven.
What has changed is that bread making has become fully automated. One automated feature, the bread slicing machine was invented in , but was slow to catch on. Americans loved this new innovation and this was when the origin of the expression "the best thing since sliced bread" was coined. Nutritional improvements also occurred during the 20th.
In late s and early s, bread was selected for a diet enrichment program in the United States. Diseases such as pellagra, beriberi, and anemia had become widespread. These diseases were associated with a lack of B-vitamins and iron. Since bread was a daily food item for most Americans, even those with poor diets, specific amounts of iron, thiamin, niacin, and riboflavin were added to white flour.
This enrichment program was a major factor in the elimination of pellagra and beriberi in the United States, as well as in reducing anemia among Americans. In , folic acid, a key nutrient in the prevention of serious birth defects, was added to all enriched grain foods, including bread.
Although the sight of mold in food is a sign that it is contaminated and should be discarded, there are some foods in which the presence of visible fungal mycelium is very much a part of the product. Among these are some of our cheeses. Two of the most familiar examples are Camembert and Roquefort, also known as blue cheese. These cheeses are among the favorites among gourmets.
These cheeses are made from two species of Penicillium , P. Among one of the earliest of manufactured foods, the discovery of the cheese making process, itself, is believed to have occurred approximately years ago. As was the case with any food that requires the addition of microorganisms, the discovery was an accidental one.
Because of the seeming magical transformation of milk into cheese, its origin, again, has been shrouded in myths and folklore. One story tells of an Arabian merchant carrying his milk with him in a pouch made from the stomach of a sheep.
This is relevant since a sheep's stomach contains rennet, an enzyme that is required in the cheese making process. Rennet is the substance that makes milk curdle and separates it into whey liquid and curd solid. By nightfall, this process had occurred and the merchant drank the whey and ate the curd. Upon his return home, the merchant told of his wonderful discovery and how satisfied he had been with his meal. In separating the liquid from the cheese, a product now existed that had much of the same qualities of milk, but now could be enjoyed as a food for a journey that would not spoil as quickly, and was also lighter than the original milk product.
It would be another years, according to some legends, before molds and other microorganisms were added to cheese for flavor. This development, again, was thought to have occurred accidentally. Afterall, why would you purposely place mold on cheese?
The origin of Roquefort Cheese, according to Roquefort publicists, long ago, a young French shepherd boy took his sheep out to graze near the little village of Roquefort. During this time a sudden downpour occurred which forced the boy to take shelter in a cave. When the rain stopped, the boy had to go out and round up the sheep so that he could take them home.
However, he had forgotten his lunch. It would be several weeks before he would return, to that particular cave, to find that his lunch was still sitting where he had left it. The bread was dried and had crumbled away and the cheese seemed to have veins of green growing throughout Figures 4a-b. Although it did not look to be very good, the boy was very hungry and took a bite from the discolored cheese, and decided that it tasted better than any cheese he had previously had.
So, the boy ran down to the village, shouting, "a miracle, a miracle," The people that gathered around the boy sampled the cheese, and from that day on they began bringing cheese to the caves around Roquefort so that it could be transformed into blue cheese. The same caves are still used for the manufacturing of Roquefort Cheese, today.
This is the story that is so often told that even schoolchildren, by the time they reach the second grade, in Roquefort, know this story, verbatim. Preparation of E. Results and Discussion 3.
Growth of Yeast and Fungi during Fermentation Figure 1 shows the growth of yeast and fungi in various types of cultures used in the fermentation of soybeans to tempeh. Figure 1. The growth curves of yeast and fungi during soybean fermentation inoculated with a single culture of S. Figure 2. The appearance of soybeans inoculated with a single culture of S. Figure 3. Figure 4. Antibacterial activities of soybeans inoculated by a culture of Saccharomyces cerevisiae , a culture of Rhizopus oligosporus , and a mixed culture of both during tempeh fermentation.
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