Fungi are unicellular or multicellular decomposers that have a thick cell wall and are responsible for decomposition and nutrient cycling throughout the environment. Surprisingly, fungi are more related to animals than they are to plants. Fungi use complex compounds as sources of energy and carbon not photosynthesis like plants. Fungi play a very crucial role in the balance of ecosystems as they colonise most habitats on earth, preferring dark and moist conditions to survive. They can thrive in the most hostile environments such as the tundra. However, most members of the Fungi kingdom grow on the forest floor where the dark and damp environment is rich in decaying debris from plants and animals. In these environments, fungi play a major role as decomposers and recyclers making it possible for members of the other kingdoms to be supplied with nutrients to survive. The food web would be incomplete without organisms that decompose organic matter. Some elements such as nitrogen and phosphorus are required in large quantities by biological systems yet they are not abundant in the environment. Fungi releases these elements from the decaying matter that they eat and this makes it available to other living organisms that require them. Trace elements are present in low amounts in many habitats and are essential for growth but it would remain tied up in rotting organic matter if fungi and bacteria didn’t return them to the environment via their metabolic activity. Fungi have the ability to degrade large and insoluble molecules and this is due to their mode of nutrition as fungi produce a variety of exoenzymes to digest nutrients. These enzymes are released into the substrate or remain bound to the outside of the fungal cell wall. Large molecules are broken down into smaller molecules which are transported into the cell by a system of protein carriers embedded in the cell membrane and the movement of small molecules and enzymes is dependent on the presence of water, active growth depends on a relatively high percentage of moisture in the environment. Fungi help to maintain a sustainable ecosystem for the animals and plants that share the same habitat and they also help to replenish the environment with nutrients as fungi interact directly with other organisms in beneficial but sometimes damaging ways. Fungi have evolved mutualisms with numerous insects as Arthropods depend on fungus for protection from predators and pathogens, while the fungus obtains the nutrients and a way to spread its spores into new environments. The fungal mycelium covers and protects the insect colonies. The scale insects foster a flow of nutrients from the parasitized plant to the fungus. Fungi can destroy plant tissue directly or through the production of potent toxins that usually end in host death and can even lead to poisoning in animals such as humans. During mycosis, fungi like dermatophytes successfully attack hosts directly by colonizing and destroying their tissues and there are many examples of fungal parasites and pathogens that causes mycoses such as Histoplasma capsulatum. A mycosis is a fungal disease that is resulted from infection and direct damage. Fungi attacks animals directly by colonizing and destroying tissues. Some individuals display hypersensitivity to moulds and spores and this can develop strong and dangerous allergic reactions. Fungi can reproduce asexually by fragmentation, budding or producing spores and sexually with homothallic or heterothallic mycelia and by producing spores too. In sexual and asexual reproduction, fungi produce spores that disperse from the parent organism by floating on the wind or travelling on an animal. The spores that are produced from fungi are defines as haploid cells and these undergo mitosis to form multicellular haploid cells. Fungi are profoundly affected by physical and physicochemical factors such as temperature, aeration, pH, water potential and light. These factors don’t just affect the growth rate of fungi but they also act as triggers in development pathways. Fungi like all living organisms require three essential factors for life which are air, food and water. Fungal growth in the indoor environment is dictated by the availability of these three factors as just like humans, most fungi breathe in oxygen which is generally abundant in indoor environments. Fungi can digest human food but also many materials that are commonly used in buildings. Fungi is grouped into four broad categories when it comes to their temperature ranges for growth. Psychrophiles (cold-loving), mesophiles which grow at moderate temperatures, thermophiles(heat-loving), Psychrophilic fungi are defined as having optimum growth at no more than 16 degrees Celsius and maximum growth of about 20 degrees Celsius. In many cases they would be expected to grow down to 4 degrees Celsius or lower whilst psychotropic fungi would be those that can grow at low temperatures but also, above 20 degrees Celsius. There are many different environments that would suit these organisms and these include the polar and alpine regions. Most fungi that are in the world today are mesophilic and these grow within the range of 10-40 degrees Celsius. However, for routine purposes, these fungi can be grown at room temperature of 22-25 degrees Celsius. Thermophilic fungi are defined as having a minimum growth temperature of 20 degrees Celsius or above and an optimum in the range of about 40-50 degrees Celsius. Most fungi are strict aerobes meaning that they require oxygen in at least some stages of their lifecycle. An example of this is Saccharomyces which require oxygen for sexual reproduction. Today, we can group fungi into four different categories in terms of their oxygen relationships. Many fungi are obligate aerobes and this means that their growth can be reduced if partial pressure of oxygen is lowered below the pressure of the air. Many yeasts and several mycelial fungi are facultative aerobes meaning that they can grow in aerobic conditions but they can grow in the absence of oxygen by fermenting sugars. Few aquatic fungi are obligately fermentative due to the fact that they lack mitochondria or cytochromes or they have rudimentary mitochondria and low cytochrome content meaning that they can grow in the presence or absence of oxygen but their energy always comes from fermentation. Light in the near- ultraviolet (NUV) and visible parts of the spectrum from 380-720 nm has little effect on the vegetative growth of fungi although it can stimulate pigmentation. In particular blue light induces the production of carotenoid pigments in hyphae and spores of several fungi. These carotenoids also occur in algae and bacteria and are known to quench reactive oxygen species. The pigments serve to minimize photo-induced damage. Melanins protect cells against reactive oxygen species and ultraviolet radiation. Aspergillosis is a fungal infection caused by the Aspergillus, a species of common mould which is found throughout the environment. Examples of this include dust, straw, grass clippings and hay. An infection normally occurs when an organism who does not cause disease infects an animal. However, this is different in the case of Aspergillosis as it does cause disease as the animal’s immune system and/ or body is weakened from a disease. The fungus can cause illness to humans and animals however, most people are naturally immune to the fungus therefore does not develop any disease caused by Aspergillus. There are two types of Aspergillus infection and these are the nasal and disseminated form. Both types can occur in cats and dogs but it occurs more frequently in dogs. Dolichocephalic and mesatcephalic breeds are more susceptible to the nasal form of Aspergillosis and the disseminated form of the disease is more common in German Shepherds. The symptoms of the nasal Aspergillosis include sneezing, nasal pain, bleeding from the nose, reduced appetite, visibly swollen nose and long- term nasal discharge from the nostril which may contain mucus, pus and blood. In some cases of the nasal Aspergillosis, loss of pigment or tissue on the surface of skin may occur. The symptoms of disseminated Aspergillosis in dogs may develop suddenly or slowly over a period of several months and includes spinal pain or lameness due to infection and can causes inflammation of the animal’s bone marrow and bones. Other signs that aren’t specific to the disease includes fever, weight loss, vomiting and anorexia. Microsporum Canis is a fungal species that causes numerous forms of disease. It is most known for causing ringworm in pet and also known to infect humans. This makes the pathogen both anthropophilic and zoophilic in nature and also is very communicable. This fungal infection mainly affects cats but will occasionally affect dogs as well. Microsporum canis is part of a fungi family known as dermatophytes. Microscopically, it has multi-celled spores known as macroconidia with rough thick walls. Macroconidia are characteristically spindle shaped with 5-15 cells. It grows white and cottony with a yellow perimeter and a bright yellow- orange underside on a culture medium. This fungus can be found in a variety of environments and survive for up to 15 months. It feeds on the keratin on the outer layers of the skin, hair and nails. Infections in animals due to Microsporum canis can manifest into ringworm and cause a scaly, crusted rash that appears as round and red patches on the skin. The fungal infection can be transmitted to humans through direct and indirect contact with animals and fomites such as combs, brushes, hats, furniture and linens. The greatest risk factor for acquiring the infection is contact with damaged cells on the skin, hair and nails as the fungal infection can infect all mammals. The clinical signs are patches of hair loss, scaling on the scalp, itching, blister like lesions, the skin may be raised or bumpy. There are ways that you can control the disease such as using medicated shampoo, ointments/ dips and oral medications. The ease of cure does depend on the severity of the fungal infection. It has been reported in cats with immuno-deficiency and cats that have poor diets.