Morphological structure of microorganisms

(1) Bacteria

Bacteria are single cells with a size of (0.
5～1)um×(2.
0～10)um
.

There are many kinds of bacteria, but the shape is no more than 3 kinds, namely spherical, rod-shaped and spiral

1.
Coccus cells are spherical or approximately spherical, and can be divided into 5 main types according to the direction of cell division and the arrangement of cells after division.
This is of great significance in classification and identification
.

(1) Monococcus
.

The two daughter cells produced after cell division are separated immediately, such as Micrococcus urea

(2) Dicoccus
.

Two new cells produced after cell separation are not separated and arranged in pairs, such as pneumococcus

(3) Tetragenococcus
.

The four cells produced after the cells divide once each on two mutually perpendicular division planes are not separated and connected into a square

(4) Streptococcus
.

The new cells produced after multiple divisions on a parallel plane are not separated and arranged into chains, such as Streptococcus lactis

(5) Staphylococcus
.

New cells formed after multiple non-directional division of cells gather into a grape shape, such as Staphylococcus aureus

2.
Bacillus cells are rod-shaped or cylindrical
.

There are significant differences in the size and specific shape of various bacilli: some are coccobacteria; some are short and thick and are short bacilli; some are long and cylindrical and are long bacilli; some are slightly enlarged and are coryneform bacilli; some One end is bifurcated and is mycobacterium

3.
The spiral bacteria cells are arc-shaped or spiral-shaped, generally solitary and able to move
.

According to the degree of bending, it can be divided into two categories: Vibrio has only one bend, which is arc or comma-shaped; the spiral of bacteria has a bending degree of more than one week, and the rotation is spiral

(2) Mold and yeast

Both molds and yeasts are eukaryotes, but yeasts are single-celled, while molds are multicellular
.
Eukaryotic cells are generally much larger than prokaryotic cells, with a size of 20-100um
.

Mold is not a taxonomic term, but a common name for filamentous fungi, that is, "fungus that can cause molds on items
.
" Mold (mycelium) is composed of a large number of filamentous hyphae, which can continuously grow from the front end and produce branches, and many branched hyphae are intertwined with each other to form mycelium
.
According to whether there is a septum in the hyphae, the mold hyphae can be divided into non septum hyphae and septum hyphae
.
There is no septum in the middle of the hyphae without septa.
The whole mycelium is a single cell with multiple nuclei
.
There is a septum in a septal hyphae.
A section of hyphae separated by the septum is a cell.
The mycelium is composed of many cells, and each cell contains one or more nuclei
.
When molds grow on a solid substrate, the hyphae are differentiated, and part of the hyphae penetrates into the substrate to absorb nutrients, which is called vegetative hyphae (substrate hyphae); the hyphae extending into the air are called aerial hyphae, aerial hyphae It can be further developed into reproductive hyphae (spore filaments) and produce spores
.
The reproductive hyphae usually extend into the air and are hollow (asexual) or bag-shaped (sporangia).
The shape, size and color of the spores can be used as classification features
.

Yeast cells are usually elliptical, spherical or columnar, and the cell size is generally (5-30)um×(1-5)um, which is about 10 times that of bacteria
.
After some yeasts (such as Candida tropicalis) undergo a series of budding, the grown daughter cells and the mother cells are not separated immediately, and they are only connected by a very narrow contact surface.
This lotus-shaped cell cluster is called "Pseudohyphae"
.
Yeast can reproduce asexually through budding, and budding is the most common method of reproduction for yeast
.
Under good nutrition and growth conditions, yeast grows rapidly, buds will grow on the cells, new buds can also be formed on the buds, and then clusters of cell clusters appear
.

(3) Viruses

Viruses are non-cellular microorganisms and are widely distributed in nature
.
They are composed of nucleic acid (DNA or RNA) and a small amount of protein
.
The protein shell is used to wrap and protect the genetic material in it
.
The two most important causes of food-borne disease outbreaks are hepatitis A virus and Norwalk-like virus, both of which are single-stranded RNA viruses
.
Hepatitis A virus is a small particle, non-enveloped, polyhedral enterovirus with a diameter of about 30nm, with a capsid outside the RNA chain
.

Related links: Classification and naming of microorganisms