Fungi can be called a "giant family" in the microbial world. Fungi are very big, and many of their members are familiar to us. For example, in wet weather, mold is often found on grains, clothes and shoes. We use Aspergillus, Mucor and other molds to make sauce, soy sauce and bean curd. Yeast used to make dough and wine are all fungi, and even mushrooms like mushrooms and auricularia are members of the fungal family. Fungi are a large class of microorganisms, belonging to eukaryotes and closely related to human beings. Fungi are the basis of various fermentation industries such as antibiotics (such as penicillin and cephalosporin) and organic acids, and play the role of decomposers of various complex organic compounds in nature. However, some fungi are pathogenic bacteria, causing diseases of people, animals and plants, and some fungi produce toxins, poisoning people and livestock, and even causing cancer in serious cases. For example, aflatoxin produced by Aspergillus flavus poisons the liver and easily causes liver cancer.

Mold is a common name for filamentous fungi, which means "moldy fungi". They tend to form lush mycelium, but they don't produce large fruiting bodies like mushrooms. In humid and warm places, many objects will grow fluffy, flocculent or cobweb-like colonies visible to the naked eye, that is, mold.

I. Form, Size and Structure of Mould

Mould mycelium is the basic unit of mould vegetative body.

Mycelium is a kind of tubular filament, which looks like a transparent hose when observed under a microscope. Its diameter is generally 3~ 10 micron, which is several times to dozens of times thicker than the cells of bacteria and actinomycetes. Mycelium can elongate branches, and many branches of mycelium are intertwined, which is called mycelium.

According to whether there is a diaphragm in the mycelium, mold mycelium can be divided into two types:

Diaphragm-free mycelium: there is no diaphragm in the mycelium, and the whole mycelium is a single cell with multiple nuclei. This is the mycelium type of lower fungi (i.e., molds in the subfamily Verticillidae and Syngnathidae).

Diaphragm mycelium: There is a diaphragm in the mycelium, and a section of mycelium separated by the diaphragm is a cell. Mycelia is composed of many cells, and each cell has 1 or more nuclei. There are 1 to many pores on the diaphragm, so that the cytoplasm and nutrients between cells can communicate with each other. This is the mycelium type of higher fungi (i.e., molds in Ascomycosubfamily and Hemimycosubfamily). Metamorphosis of fungal hyphae In order to adapt to different environmental conditions and absorb nutrients more effectively to meet the needs of growth and development, many fungal hyphae can differentiate into some special shapes and tissues, which is called hyphal metamorphosis.

Haustorium: Metamorphosis of hyphae caused by specific parasitic fungi such as rust, downy mildew and powdery mildew, which is a lateral branch produced by hyphae, invades cells, differentiates into roots, fingers, balls and bergamot, and absorbs nutrients in host cells.

Rhizomatous stem: Rhizopus mycelium contacts with nutrient matrix to form rhizomatous structure, which has the function of fixing and absorbing nutrients.

Bacterial nets and rings: the hyphae of some predatory molds are transformed into rings or nets, which are used to catch other small organisms, such as nematodes and paramecium.

Fungal rings and fungal nets a. Fungal rings; B. simple bacterial net; C. Complex bacterial web

Sclerotium: dense tissue formed by a large number of hyphae, which is dormant and can resist adverse environmental conditions. Its outer layer is hard and dark; The inner layer is loose and mostly white. For example, medicinal poria cocos and ergot are sclerotia.

Sclerotinia sclerotiorum

Fruit body: specialized by a large number of aerial hyphae. Fruit body refers to any structure with a certain shape that can produce spores in or on it. For example, there are three kinds of complex fruiting bodies that can produce sexual spores, which are called ascomycetes, ascomycetes and ascomycetes.

Second, the propagation of mold.

Mold has strong reproductive ability and various reproductive methods. Although any segment of fungal mycelium can develop into a new individual under suitable conditions, in nature, fungi mainly reproduce by producing various asexual or sexual spores. Spores are a bit like seeds of plants, but they are extremely numerous and small in size.

The asexual spores of mold are directly formed by the differentiation of reproductive hyphae, and the common ones are arthrospores, chlamydospores, sporangium spores and conidia.

Arthrospore: A cell formed by the growth of mycelium to a certain stage, the appearance of diaphragm, and then breaking from the diaphragm is called arthrospore. Such as arthrospores produced by Geotrichum candidum.

Chlamydospore: Some mold species have local cytoplasm concentration and cell wall thickening in the middle or top of hyphae, and finally some thick-walled resting spore is formed, which is called chlamydospore. Such as Mucor racemosa in Mucor.

Mould arthrospore

Spores: Spores formed in sporangia are called sporangia. Sporangium is formed by the expansion of cells at the top of hyphae, and a diaphragm is formed below the expanded part to separate hyphae. The protoplasm of the expanding cell differentiates into many small pieces, and each small piece can develop into a spore. There are two kinds of sporangium spores, one is flagella, and the swimming spores are called swimming spores, such as Tricholoma of Flagellaceae; The other is called static spore, which does not produce flagella and cannot swim, such as Rhizopus of Syngnathidae.

The swimming spores of mold The rest of the static spores of mold are: the sporangium of Mucor; Medium: the sporangium wall is broken, revealing static spores; Right: Capsule Axis

Conidia: Spores formed on the top of reproductive hyphae or differentiated conidiophore. Conidia are arranged in a single, chained or clustered way, which is an asexual spore produced by fungi of Ascomycetes and Semifungi. Adhesion and morphology of mold conidia (Penicillium, Aspergillus, Fusarium)

Aspergillus conidia and Fusarium conidia on the apical sac; Color Atlas of Conidia Head of Penicillium Brush conidiophore and Aspergillus Conidia.

Sexual reproduction and spores of mold;

Spores formed by the combination of bisexual cells are called sexual spores. The process of sexual reproduction of mold is generally divided into three stages, namely, mass matching, nuclear matching and meiosis.

Cytoplasmic matching is that the protoplasm of two partner cells are fused in the same cell, but the two nuclei are not combined, and the number of chromosomes in each nucleus is haploid.

Nucleation is the combination of two nuclei into a diploid nucleus.

Meiosis restores the number of chromosomes in the nucleus to the original haploid.

Sexual spores are not as frequent and abundant as asexual spores, and are often produced only under certain special conditions. Common ones are oospores, zygospores, ascospores and basidiomycetes, which are produced by molds of Verticillinae, Arthrobacter, Ascomycomycetes and Basidiomycetes respectively.

Oospore: Mycelium differentiates into different shapes of male organ and egg storage, and the sexual spore formed by the combination of male organ and egg storage is called oospore.

Oospores of mold 1 Male organs; 2. Egg storage device; 3. Oospores

Synspore: a sexual spore formed by the combination of hyphae that differentiate into two gametophytes with the same shape but different sex, called zygospore.

Ascomycete spores: Mycelium differentiates into Ascomycetes and male organs, which combine to form Ascomycetes, and the sexual spores formed in Ascomycetes are Ascomycetes.

Basidiospore: Mycelium undergoes special differentiation and sexual combination to form basidiospores, and the sexual spores formed on basidiospores are basidiospores.

Conjugated spores of mold

Left: (+) and (-) hyphae of Mucor combine at the junction to produce black bands, which can be seen by naked eyes;

Right: Take a small black spot and observe the zygospore with a microscope.

Ascomycetes of mold

A. ascocarp; B. Ascomycetes; C. false lateral line; D. ascospores

Schematic diagram of basidiospore formation process

A ~ D. binuclear cells; E. nuclear fusion; Nuclear division; Formation of basidiospores; Basidiospores mature and release.

The spores of mold are small, light, dry and abundant, with different shapes and colors, long dormancy period and strong resistance. Each individual often produces tens of thousands of spores, sometimes reaching tens of billions, hundreds of billions or even more. These characteristics help mold to spread and multiply everywhere in nature. For human practice, these characteristics of spores are beneficial to inoculation, expanded culture, strain breeding, preservation and identification, but its disadvantage is that it is easy to cause pollution and spread mold and mycosis to animals and plants.

Third, the colony of mold.

Because the mycelium of mold is thick and long, the colony of mold is large. The hyphal spread of some molds is unrestricted, and their colonies can extend to the whole Petri dish, while others have certain limitations, with the diameter below 1~2 cm. Generally, the colony texture is looser than actinomycetes, and its appearance is dry and opaque, showing a dense or loose spider web, fluff or cotton wool; Colonies are closely related to the culture medium and are not easy to pick. The colors of the front and back of colonies and the colors of the edges and centers are often inconsistent.

Colonies of various Aspergillus species

Penicillium colony of various pathogenic fungi