Table of Contents
Bacteria from a large group of unicellular prokaryotic cells that don’t contain nuclei and other membrane-bound organelles. They were first absorbed by Antonie van Leeuwenhoek in 1676 using a single-lens microscope. A microscope of his own design, called “Animalcule.”
There are mainly two groups of bacteria: Archaebacteria and Eubacteria. They are various shapes, like bacillus (a rod shape), coccus (a sphere shape), spirillum (a spiral shape), and vibrio (a curved rod shape). They are motile or non-motile.
Structure of bacteria
In the ultra-microscopic structure of bacteria, it is seen that it has a small capsule-like structure. In the structure of bacteria, the following parts are present: capsule, cell wall, cell membrane, flagella, cytoplasm, nucleoid, inclusion body, mesosomes, ribosomes, and pili.
It is the outermost, thickest, and slipperiest structure, and it is rigid and flexible. The composition of the capsule is about 98% water and 2% glycoprotein. This glycoprotein is of different types in different bacteria, like homopolysaccharide, hemi polysaccharide, and heteropolysaccharide.
Function: The capsule is preventive by nature and protects the bacteria from mechanical injury, temperature, and drying. It helps in attachment and repulsion with other bacteria. It acts as antiphagocytic.
2. Cell wall
It is a thick structure present below the capsule, and it is made up of peptidoglycan layers. On the basis of the cell wall, bacteria are identified as gram positive or gram negative. In gram-positive bacteria, about 20-30nm thickness of peptidoglycan are present and in gram-negative bacteria, its thickness is 7-8 nm. Peptidoglycan is a polymer of the two sugar molecules NAG and NAM.
Function: The main function of cell wall to provides shape to bacteria and identification.
3. Cell membrane
A cell membrane is a thin layer that is present in prokaryotic cells or bacteria. It is composed of 20–30% phospholipid and 60–70% protein.
Function: The main function of the cell membrane is to act like the SPM.
It is long thick hair like structure, which is surrounded by sheath. Its diameter is 20nm and its length is 15–20 nm. It is made of flagellin protein.
Function: It act like antenna which helps in searching food and danger. It also helps with locomotion.
5. Inclusion body
Various types of organic and inorganic food material are stored in this body.
The less developed nucleus without nucleoplasm and the nuclear membrane is called the nucleoid. In the nucleoid of bacteria, about 60% DNA, 30% RNA and 10% protein are present.
Mesosomes are present in the cell membrane of bacterial cells, which helps in cellular respiration.
In bacteria, the 70S type of ribosome is present, which helps in protein synthesis.
It is a small, thin, 8–10-hair-like structure that helps in the attachment of bacteria to other bacteria and the transfer of generic material.
Morphological classification of bacteria
On the basis of structure, shape, size, and appearance, bacteria can be classified into two categories:
1. True bacteria
They are the group of bacteria which shows the real characteristic of bacteria. It has two types: Cocci bacteria and Bacillus bacteria.
1. Coccus bacteria: These bacteria are spherical or oval shaped, these are further classified as: monococcus(In which cocci is in single form), diplococcus(In which cocci is in pair), tetra coccus(In which cocci is in group of four), streptococcus(Coccus is in chain form), sarcino coccus(Cocci is in group of eight or in the form of cube).
2. Bacillus bacteria: These bacteria are rod shaped bacteria, these are classified as: Mon bacillus(In which Bacilli is single form), diplobacillus(In which bacilli is in pair), tetra bacillus(In which bacilli is in group of four), streptobacillus(Bacillus is in chain form), sarcino bacillus(Bacillus is in group of eight or in the form of cube).
2. False/Pseudo bacteria
These are those bacteria which are a bacteria but their shape in different from bacteria. It shows different characteristics than bacteria, like fungi, viruses, and protozoa. They can be further categories as:
- Actinomycetes: These are rigid organisms like true bacteria, but they resemble fungi in that they exhibit branching and tend to form filaments. They are filamentous in shape, and branching is present. That are gram-positive in nature. They are present in soil; they are heterotrophic aerobic and mesophilic bacteria. Ex- mycobacteriaceae
- Spirochetes: These are relatively longer, slender, non-branched microorganisms with a spiral shape. They are chemotrophic in nature and gram-negative bacteria. The length of this bacteria is between 3-500um. Ex- leptospirainterrogans.
- Mycoplasma: These are in oval shaped and these are lack in rigid cell wall (cell wall lacking) and not developed properly. They are smallest bacteria; it’s look like virus and pathogenic in nature. Ex- pneumoniae and genitalium.
- Rickettsia: Rickettsia are non mortile, gram negative and non-spore-forming bacteria. They are present in cocci, bacilli, and thread-shaped forms. This bacteria is pathogens and responsible for different fever. Ex- rickettsiaconarri and R-typhs.
- Chlamydia: They are ovoid in shape and gram-negative bacteria; its cell membrane is consisting of peptidoglycan and other proteins. They are very small, obligate parasites. The commonly effect the human eye. Ex- C-pneumonia and C-psittacine.