Molds are eukaryote (or true nucleus) organisms, which belong to Fungi kingdom. Molds grow in the form of multi-cellular filaments called hyphae. These tabular branching hyphae form a network, which is known as mycelium and is considered to be a single organism. The hyphae are separated by septa (wall) into multiple compartments, which contain single or more than one, genetically identical nuclei. The “fluffy” look of most of the molds is caused by differentiation at the ends of hyphae, which form asexual spores (known also as conidia). Some mold species form spores in different colors. The mode of spore formation, their shape and color is used to classify molds.
Molds can grow on a many different materials: soil, food, decaying plants, fabrics, and damp walls. One very important requirement for their effective development and reproduction is the availability of moisture. If the environmental conditions are appropriate, molds develop very fast and they reproduce by releasing huge numbers of tiny spores. These spores can survive really extreme environmental conditions, like drying and freezing. Molds does not photosynthesize. Their feeding rely on biodegradation of natural materials. In most of the cases the mold biodegradation is considered as unwanted when cause food spoilage or damage of in-house properties, but in nature it is highly beneficial process because it facilitates the circle of life – they are essential for the breakdown of dead organic matter in the natural environment. Although not direct, molds have also importance for human health and well being, because they are used for production of drugs (like some antibiotics) and are used in the food production.
What is mold and why molds spread everywhere
Environments preferred by mold
Molds have quite diverse life-styles, but the majority of them are them are saprotrophs. Molds grows best in moderate temperature (they are mesophyles), but some of molds could survive in extremely hot (thermophiles) or cold (psychrophiles) conditions. Besides the temperature requirements, they all need moisture for their growth. Some mold species even live in aquatic conditions!
How do mold feed?
Molds are heterotrophs – they derive the energy energy they need not by photosynthesis, but from the organic matter on which they live. Molds molds produce hydrolytic enzymes, which are then excreted from the hyphal tips to the surrounding organic matter of their habitat. The hydrolytic enzymes are able to degrade complex biopolymers (such as starch, cellulose and lignin) into monomers which then can be absorbed by the hyphae. In this way molds enable the recycling of nutrients throughout ecosystems as they decompose the organic material. Some molds can also grow on most commonly used foods by humans and animals. Their development can make these foods unpalatable or even toxic. Thus molds can be considered as a major source of food spoilage and food borne illnesses. There are multiple food preservation methods, like salting, pickling, freezing, drying, which aims to prevent or slow down the growth of molds and/or other microbes.
Reproduction of mold
Mold reproduce via large numbers of small spores, which may contain a single or multiple nuclei. These spores can be asexual (generated through mitosis) or sexual (generated as part of a meiosis process). Many species can even have both types of spores. Molds which rely on wind dispersal usually produce small, hydrophobic spores. These spores may remain airborne for really very long periods. Other mold, which use water as main carrier, have spores with slimy sheaths.
The spores of the mold greatly vary in their shapes and sizes. Most of the mold have spherical or ovoid single cell spores, but there can be also multicellular and variously shaped. Some of the spores are able to survive extremes conditions in terms of temperature and/or pressure.
Most common types of mold
Fungal molds represent a wide variety of species mostly from Zygomycota, Ascomycota, and Basidiomycota phyla. One of the most famous mold representing this group is the bread mold Penicillium, which led to the discovery of antibiotics. Another important member of the group is Stachybotrys chartarum, one of the species related to “sick building syndrome”.
Slime molds represent a group of non-fungal species, such as Lycogala epidendrum or Fuligo septica. These slime molds are more closely related to the single-celled Amoeba. The representative species of this group live most of their life as single cells and wander through it’s habitat eating different types of bacteria. However, when a specific chemical signal is received from the environment, this causes them to aggregate on a single spot and form a microbiotic group. Usually these formations are large enough to become visible to the naked eye. In addition these groups have spore-producing structures which facilitates the molds propagation.
Water molds do not form multicellular formations that are visible to unarmed eye and thus don’t quite fit the common idea of a mold. However their microscopic structure is very close to that of the fungal molds and under the microscope they could be mistaken with some fungal molds (as it was done originally!). Most of the organisms in this group belongs to Oomycetes and are more closely related to kelp than all other groups of molds. Some of the members of this group are plant pathogens like the one that cause potato blight – Phytophthora infestans; and another one that is the reason for sudden oak death – Phytophthora ramorum.
Molds benefits – Molds in food production and pharmaceutical use
Many molds species are widely used in food production process. For example members of Aspergillus genus (like Aspergillus oryzae and A. sojae) have been cultivated to ferment a soybean and wheat mixture to produce soy sauce and derivate products. Koji molds are used for the fermentation of rice and production of sake and other distilled spirits. Red rice yeast (Monascus purpureus) contains several important compounds known as monacolins. There are studies that show that these compounds can inhibit cholesterol synthesis and may help decrease “bad” cholesterol. Molds are used as starter cultures in the production of specific brands of sausages. These molds provide specific flavour and reduce bacterial spoilage during curing. Other molds participate in the maturation and flavouring of cheese and other diary products.
It is already an encyclopedic example, that Alexander Fleming discovered of the antibiotic penicillin by accident. The responsible mold is a member of a Penicillium genus, although the species identity is still disputable. The molds metabolism is also a source for statin cholesterol-lowering drugs, such as Lovastatin which is produced by Aspergillus terreus. Molds are source for another important class of drugs like immunosuppressants, which are applied to suppress rejection the newly transplanted organs – the drug cyclosporine is derived from the mold Tolypocladium inflatum.
Molds at home and health effects
People have lived with molds for thousands of years. However, in the current domestic setting, molds can cause serious damage of in house property and even can result in health problems. For example, black molds usually develops on damp surfaces (such as the walls in the bathrooms) and may damage it’s structure. Even worst, when large quantities of spores are released, this can induce large variety of health issues, like coughing, sneezing, eye-irritation, and skin rash. These unpleasant reactions could even go worsen for people with asthma and could result in really severe breathing difficulties.
In the outdoors the molds’ spores do not pose any direct threat to human health because they are present is a considerably low concentrations. It is a completely different story when when they are released in vast amounts in an indoor space where they may have significant health effects. The spores are designed to survive extreme conditions, but the molds themselves require moisture and appropriate temperature to grow. The ideal places for them are the areas in your home with elevated humidity, medium temperature, poor air circulation and limited amounts of natural light. Having in mind the above, it is not surprisingly that they are common in bathrooms and basements. In such appropriate conditions, molds can germinate and spreads rapidly everywhere.
Particular mold species can produce mycotoxins that can cause serious health issues to humans and animals. Prolonged exposure to high levels of mycotoxins can lead to serious neurological problems and in some cases even death. Usually the term “toxic mold” is used to name molds that produce mycotoxins and not to all molds in general. Molds could be even more harmful for human and animal health when they are consumed after growing on certain stored food. Some species produce toxic secondary metabolites (again mycotoxins) like aflatoxins, fumonisins, citrinin, ochratoxins, and patulin. Note that not all mycotoxins are harmful to humans, even more some of them are used for the benefit of humans. These are the cases when the mycotoxin toxicity is directed against other organisms but not humans. A very popular example is penicillin, which affects the growth of Gram-positive bacteria, some spirochetes and fungi.