Fungi on Land, Water, and Even on Your Dinner Plate

The pleasure of having a stuffed portobello or grilled shiitakes on your dinner plate can be rivaled by the horror of finding a fungus such as mold in your apartment. Fungi are simply everywhere with over 100,000 species currently known. Only around 100 of these are regularly appearing pathogens to humans. These species can cause diseases of the skin, mucous membranes, nails, airways, as well as possible systemic diseases—deep infections of the internal organs.

The Greeks occasionally referred to fungi as sponges (sphongos/σφογγος), resulting in the later Latinization fungus, meaning mushroom. This incredibly unique life form, which appears in various and strange forms, has always had an important role in many world cultures. Yeast fungus was used very early for the production of food and drinks such as bread, wine, cheese, and beer. Mushrooms were eaten like any other food item, employed as treatments for diseases, and were even utilized as hallucinogenic drugs. Still today, fungi are the constant companions of humans—yet even this has its downside.

Neither Fish Nor Fowl

Animal, plant, or fungus? This is a controversial matter disputed by biologists. The physiological characteristics of fungi speak for categorizing them as part of the animal kingdom as they feed on organic material. However, they were long classified as plants because of their inability to move. Yet unlike plants, they lack chlorophyll and are not able to photosynthesize, thus they have an animal-like metabolism. Today, these life forms are classified as themselves: fungi.

The size of fungi ranges from tiny species that can only be seen through a microscope or the micromycetes up to large species that can be seen by the naked eye or the macromycetes.

Fungi are categorized into three groupings:

Budding fungi or yeasts are single-celled fungi that are round or oval shaped. Normally they appear alone, but sometimes several cells are connected and referred to as pseudohyphae as they mimic the long shape of hyphae. Most yeasts do not require oxygen to survive, thus they are facultative anaerobic.
Filamentous fungi (mold) are hyphae or mycellium fungi. They are composed of filamentous cell connections, the hyphae, which create large, bushlike, branching structures. The hyphae network is referred to as a mycellium (or sometimes shiro), and the entire mycellium is referred to as a fungal colony or a fungal thallus. Filamentous fungi grow on a fixed location: on soil, wood, plants, or other organic material. Some even have the familiar mushroom cap (sporocarp), some of which are the edible Agaricomycetidae. Filamentous fungi develop clever strategies for food intake; many species are even able to create small nooses under the soil, which they use as booby traps to catch tiny nematodes and worms.
Dimorphic fungi are actually hybrids of the aforementioned fungi. They are able to adapt to their environment and grow into either yeast or hyphae. This process is known as dimorphism.

Small Cells with Plenty of Power

According to their size, fungi can be composed of one (yeast) or a multitude of cells. The structure of all fungus cells is fundamentally the same. The cells are immobile and are approximately 2 to 10 micrometers in size (µm)—just about twice as large as a bacteria.

Fungus cells are categorized as eukaryotic, which means that they possess a nucleus with a nuclear membrane in their cytoplasm. Also to be found in the cytoplasm are ribosomes, which are primarily composed of RNA and proteins. The mitochrondia are the small power plants of the cell responsible for the production of energy as well as the cell cycle and growth processes. The cytoplasm is contained and protected by the cell wall, a resilient structure built of chitin.

Hyphae fungi are composed of multiple cells that are combined to create the individual hyphae. Between these cells there are partition walls called septa whose pores allow the exchange of cytoplasm.

Grow. Reproduce. Repeat.

Fungi have an ability to grow at incredible speeds. They can truly multiply and expand in a very short amount of time of less than 30 minutes. This applies especially true for the sporocarp, the mushroom caps that grow on soil. The mycelium is also able to propagate at noticeable speeds. Fungi have been observed to grow up to one kilometer of hyphae in just one day. The growth of fungi is especially fast in a moist, warm, dark, and acidic environment (ideally at a pH level of 5).

Fungi reproduce either asexually (fungi imperfecti) or sexually (fungi perfecti). The fungi perfecti, the “true” fungi, are hyphae fungi, which consist of a mycelium and a mushroom cap (sporocarp). Reproduction occurs through sexual spores, zygotes, which carry the genetic material as a double chromosome set. The zygotes are created through the fusion of two gametes, each of which carries a single set of chromosomes, a process quite similar to the fusion of a human egg cell and sperm cell.

Fungi imperfecti asexually create spores as a means of reproduction. The spores are created on the hyphae through budding, the origin of the name “budding fungi.” Another method of reproduction is the pullulation or pinching off of new cells. Some fungi break up their own hyphae into smaller pieces as a means of reproduction.

Refined Delicacies and Helpful Allies

Today's kitchens are not imaginable without the helpful single-celled yeast fungus used in baking. It would bring tears to many people's eyes to think of a world without beer (brewed with yeast) or certain fine cheeses (made with penicillin and other fungi cultures).

At the top of the list of acceptable and useful fungi is surely the truffle. Truffles are sold at prices per kilo comparable to the price of a diamond necklace and are one of the most expensive luxury articles in the world. Other edible mushrooms can be purchased at reasonable prices or gathered in the forest and can be just as delicious.

In the medical and therapeutic arena, fungi have also become indispensable. Antibiotics produced from fungi are referred to as mycoine. Penicillin is such an antibiotic produced using the mold Penicillium notatum. Other fungi are used as medicinal mushrooms in mycotherapy.

Fungi feed on organic material created by other life forms (heterotrophic). The metabolism of fungi additionally provides for biological decomposition. Gardeners are pleased with the end result: humus, a mineral-rich and organic soil.

Toxic Toadstools and Murderous Molds

Some large mushrooms such as the fly amanita are highly toxic; consumption can lead to death. Similarly poisonous are ergot mushrooms (ergoline) that grow on the flowers and spikes of rye and other grains and grasses.

The largest health problem for humans is posed by pathogenic yeast and mold fungi, which affect us in various ways:

Approximately 300 types of these microorganisms produce so-called mycotoxins, products of their metabolism that are toxic in small amounts. Considered carcinogenic, mycotoxins are transmitted by air or by ingesting moldy food.
Spores of fungi can also arrive in the body through the airways. Germination and eventual fungi colonization in the body is possible because the body provides the fungus with a favorable climate—warm and moist. A healthy immune system is normally able to hinder the germination or prevalence of these pathogens. However, if the immune system is weak and there is an imbalance between the fungi and the host, an infection can occur. AIDS and leukemia patients are highly vulnerable to an infection. Additionally, people with age-related immunodeficiency, chemotherapy patients, patients with transplanted organs, or people who use antibiotics have increased chances of suffering from an opportunistic fungal infection. A colonization of yeast or mold fungi can cause both superficial and systemic mycosis. In the case of superficial mycosis, all mucous membranes and the skin are susceptible, although it is most often the feet (athlete's foot) or the nail beds that become infected. In the case of systemic mycosis, the pathogens arrive in the organs through the bloodstream and can cause very serious sicknesses, such as disruptions of the nerve and kidney functions.
Yeast and mold fungi can also provoke allergic reactions that most often result in chronic cold-like symptoms or bronchial asthma.

Yeast and mold fungi are also the catalysts of nosocomial infections, the so-called hospital infections.

Battling the Fungus Among Us

Fungal infections are usually easily treatable—only systemic mycosis can eventually lead to life-threatening situations. There is no effective immunization against fungi, and they can only be treated with anti-fungal agents. Antifungal agents are either fungicidal or fungistatic and are applied locally or systemically. The agents always have the target of destroying the cell walls of the fungus. This occurs by either increasing the porousness of the walls so that the cell components are lost or simply the creation of the cell wall components themselves.

Local application of anti-fungal agents can take the form of ointments, lozenges, suppositories, or solutions. In the case of systemic sicknesses, the active agent (e.g., amphotericin) must be applied intravenously. Higher dosages increase the risk of severe and potentially lethal side effects such as high fever, shaking chills, hypotension, anorexia, nausea, vomiting, headache, dyspnea, and tachypnea.

Yeast and mold fungi are not only satisfied with the environment of organic nutrients. They can also survive on or within moist materials, such as cleaning rags or many water solutions. Any synthetic material or clothing that does not breathe well like your sport shoes offer the mold a pleasant hiding place. There is a range of fungicidal disinfectants available for use against fungus outside the human body.

In the dentist's office, some fungi appear quite often. These fungi will be identified and described below. This does not mean that other fungi will not be present.