Bacteria are a class of prokaryotic microorganisms. They are a kind of prokaryotic organism with short shape, simple structure and multi-divisional reproduction. It is the most widely distributed organism in the natural world and the main body of natural material circulation. By.
Dichotomous division is the most common and dominant mode of reproduction of bacteria. Before splitting, the cells are prolonged, the chromosomes are duplicated, and then split perpendicular to the long axis. The plasma membrane near the equator of the cell grows concave until a diaphragm is formed, and a transverse wall is formed, thus producing two daughter cells.
After a single or a small number of bacterial cells grow and multiply, a cluster of sub-cells with a morphological structure and a certain morphological structure centered on the mother cell is formed. This is a colony. Bacterial colonies often appear to be moist, viscous, smooth, transparent, easy to pick, uniform in texture and the color of the colony front or back or the edge and the central part. The colony characteristics of bacteria vary from species to species.
When many colonies are joined together, they are called lawns. Colonies can be used as an important basis for judging purity and preliminary determination of the type of strain.
However, in a few bacteria, there are other ways of reproduction, such as unequal two division, budding reproduction, three divisions and multiple divisions. The unequal division is a variant of the two divisions, and the reproduction of the stalk bacteria is a typical example.
There are three basic forms of bacteria: globular, rod-shaped and spiral, which are called cocci, bacilli and spirochetes.
The size of the cocci is expressed in diameter and is mostly 0.5-1.0 microns. Classification is based on the arrangement of cells after division.
After the cell divides, the new individual is dispersed and exists alone, which is a single bacterium.
The two cells are arranged in pairs and are diplococcus.
The four cells formed by two divisions are combined in a field shape and are four-cocci.
A plurality of cells are arranged in a chain and are Streptococcus.
The cells divide in three mutually perpendicular directions, and the eight cells after the division are stacked together in a cube shape, which is a sclerotium.
The cells are not directionally split, and the new individuals formed are arranged in a grape cluster and are Staphylococcus.
The size of the bacilli is expressed by width x length, typically 0.2-1.25 x 0.5-5.0 microns. Divided into single bacillus, double bacillus, streptococci and the like. The bacillus has different shapes at both ends, such as blunt round, flat or slightly pointed. The ratio of length to diameter of various bacilli varies greatly, some are short and thin, and some are slender. Bacillus is the most abundant species in bacteria, such as Escherichia coli, Bacillus subtlis, etc.
The size of the spirochetes is generally 0.3-1.0×1.0-50 micrometers, and is classified into two types according to the degree of cell bending and the number of spirals. If the bacteria are bent less than one turn, it looks like a comma, called Vibrio, such as Vibrio cholerae; when the bacteria rotates like a spiral, it is called spirulina, such as Spirillum minus.
In addition, there are some special forms of bacteria, such as red micro bacteria with filaments, filamentous bright hair bacteria.
Bacterial cells are prokaryotic cells, that is, there is no nuclear structure in the cells, only the obvious nuclear region (nuclear), surrounded by no nuclear membrane. Compared with eukaryotic cells with true nuclei, other structural components are also different. For example, the main component of the prokaryotic cell wall is a kind of polysaccharide containing amino acids called peptidoglycan, and the eukaryotic cell wall is mainly composed of cellulose or chitin.
Identification of bacteria
At present, the identification of bacteria can be roughly Gram stained mirror, selective culture, etc. These are preliminary screening; further biochemical reaction identification and serotyping based phenotypic identification techniques, in which biochemical reactions include traditional biochemical reactions Identification, commercial API strip identification, VITEK bacteria identification instrument, etc.; in addition, chromatographic and mass spectrometry typing and molecular biotechnology-based identification.
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