Source of mold

In the hot summer, many foods go bad because the high temperature inside causes the bacteria to grow rapidly. People have found a kind of bacteria in these foods, which is mold. If people eat mold by mistake, they will have symptoms of poisoning, which will affect the human body. Mold is often found in people's lives, so what is the source of mold? Let’s learn about it together~

Mold is a part of fungi, and its characteristics are that its mycelium is well developed and there are no large fruiting bodies. Like other fungi, it has a cell wall and can survive as a parasite or a saprophyte. Some molds transform food into toxic substances, while others may produce toxins in food, namely mycotoxins. Since the discovery of aflatoxin, food contamination by mold and mycotoxins has attracted increasing attention. It causes great harm to human health, mainly manifesting in chronic poisoning, carcinogenicity, teratogenicity and mutagenicity.

1. Mold

Mold is a general term for fungi that form branching hyphae. It is not a taxonomic term, but belongs to the various subphyla of the phylum Fungi. The basic unit that makes up the fungus is called hyphae, which is long and tubular, 2 to 10 microns wide, and can continue to grow and branch from the front end. Without or with septa, with 1 to more nuclei. The cell wall is divided into three layers: the outer layer is amorphous β-glucan (87nm); the middle layer is glycoprotein, and the protein network is filled with glucan (49nm); the inner layer is chitin microfibrils, interspersed with amorphous proteins (20nm). When growing on a solid substrate, some hyphae penetrate deep into the substrate to absorb nutrients, which are called matrix hyphae or nutritional hyphae; those extending into the air are called aerial hyphae, which can further develop into reproductive hyphae and produce spores. A large number of hyphae interwoven into a villi, floccules or net-like shape is called mycelium. The mycelium is often white, brown, gray, or brightly colored (colonies with white hairy shapes are Mucor, green are Penicillium, and yellow are Aspergillus flavus), and some can produce pigments to color the matrix. Molds reproduce rapidly, often causing large amounts of food and utensils to rot and spoil, but many beneficial species have been widely used. They are the earliest type of microorganisms used and recognized in human practical activities.

Mold is the common name for filamentous fungi, meaning "moldy fungi". They often form branched mycelium, but do not produce large fruiting bodies like mushrooms. In moist and warm places, they grow on many items. The fluffy, floc-like or spider-web-like colonies visible to the naked eye are mold. Its cell wall is mainly composed of chitin, so it should be distinguished from Streptomyces (actinomycetes).

2. Characteristics of mold colonies:

A. Large in shape, loose in texture, dry in appearance, opaque, and either loose or tight in shape.

B. The connection between the colony and the culture medium is tight, making it difficult to pick up. The color and structure of the front and back of the colony, as well as the color and structure of the edge and center are often inconsistent.

C. The hyphae of mold are differentiated into vegetative hyphae and aerial hyphae, but aerial hyphae do not have capillary water, so their colonies must be different from those of bacteria or yeasts and are closer to actinomycetes.

Mycelium of mold. The basic unit of fungal vegetative body is hyphae. Mycelium is a tubular filament that looks like a transparent rubber tube when observed under a microscope. Its diameter is generally 3 to 10 microns, which is several to dozens of times thicker than that of bacteria and actinomycete cells. The hyphae can elongate and branch, and many branched hyphae intertwined with each other are called mycelium.

Depending on whether there are septa in the hyphae, mold hyphae can be divided into two types: non-septate hyphae and septate hyphae. There are no septa in the aseptate hyphae, and the entire mycelium is a single cell containing multiple nuclei. This is the type of hyphae possessed by lower fungi. There are septa in the mycelium. A section of mycelium separated by the septum is a cell. The mycelium is composed of many cells, and each cell has one or more nuclei. There are one or more small holes on the septum, allowing the cytoplasm and nutrients between cells to communicate with each other. This is the type of hyphae possessed by higher fungi.

In order to adapt to different environmental conditions and absorb nutrients more effectively to meet the needs of growth and development, the hyphae of many molds can differentiate into some special forms and tissues. This specialized form is called mycelial metamorphosis.

3. The fungal hyphae growing on solid culture medium can be divided into three parts: ① Vegetative hyphae: hyphae that penetrate deep into the culture medium and absorb nutrients; ② Aerial hyphae: hyphae that grow into the air; ③ Reproductive hyphae: some aerial hyphae develop to a certain stage, differentiate into reproductive hyphae, and produce spores.

Haustoria: A metamorphosis of mycelium produced by obligate parasitic fungi such as rust, downy mildew and powdery mildew. They are side branches that grow from the mycelium, invade the cells and differentiate into root-like, finger-like, spherical and Buddha's hand-like shapes to absorb nutrients from the host cells.

Rhizoid: A root-like structure differentiated from the contact between the hyphae of Rhizopus fungi and the nutrient matrix, which has the function of fixation and absorbing nutrients.

Mycelial webs and rings: The hyphae of some predatory fungi are metamorphosed into rings or nets, which are used to capture other small organisms such as nematodes, Paramecium, etc.

Sclerotium: A dense mass of hyphae that is a dormant body that can withstand adverse environmental conditions. The outer layer of tissue is hard and dark in color; the inner layer is loose and mostly white. For example, medicinal Poria cocos and ergot are both sclerotia.

Fruiting body: It is specialized from a large number of aerial mycelium. Fruiting body refers to any structure with a certain shape inside or on which spores can be produced. For example, there are three types of complex fruiting bodies that can produce sexual spores, called cleistothecia, ascothecia, and ascothecia.

Because the hyphae of mold are thick and long, the mold colony is larger. The hyphae of some molds spread without limitations, and their colonies can expand to the entire culture dish. Some species have certain limitations, with a diameter of 1 to 2 cm or smaller. The texture of the colonies is generally looser than that of actinomycetes, and they are dry and opaque in appearance, presenting a tight or loose spider-web, fluffy or cotton-like shape; the colonies are tightly connected to the culture medium and are not easy to pick up; the color of the front and back of the colonies and the color of the edges and the center are often inconsistent.