Structure of Bacteria and classification
Introduction
Bacteria are unicellular prokaryotic organisms, lacking well-defined nuclei and membrane-bound organelles. These organisms are essential to
life on Earth. A huge variety of shapes and sizes of Bacteria are present
ranging from minute spheres to larger filamentous chains.
Bacteria are known for their simple body structure. A cell
envelope consists of an interior cytoplasmic membrane, the cell wall, and- in
some species of bacteria- an outer capsule.
Structure of a bacteria
The structure of a bacterium is relatively simple,
consisting of three main parts:
The cell membrane of bacteria:-
The cell membrane of bacteria, also known as the cytoplasmic membrane, is a selectively permeable barrier that surrounds the cytoplasm of bacterial cells.
It is made up of a lipid bilayer, which is composed of phospholipids, glycolipids, and other lipids. The membrane plays essential roles in maintaining the cell's shape, protecting the cell from its environment, and controlling the movement of molecules in and out of the cell.
Additionally, it also contains various proteins, such as transporters, pumps, and channels that allow specific molecules to enter and exit the cell. The cell
membrane is also an important target for antibiotics, which can disrupt its
function and lead to the bacterium's death.
label diagram of bacteria |
The cell wall of bacteria:-
Each bacterium is enclosed by a rigid cell wall composed of
peptidoglycan. Its function is to give the cell its shape and protect the
cytoplasmic membrane from the environment. Call wall composition varies widely
amongst bacteria and is used to analyze and differentiate bacterial species.
The capsule is made up of polysaccharides. Its function protects the bacterium from phagocytosis and keeps it from drying out.
Also, read
Antibacterial drugs |definition, classification, uses
The cytoplasm of bacteria:-
The cytoplasm is the site where the functions of cell
growth, metabolism, and replication take place. It is a gel-like matrix composed
of water, enzymes, wastes, and gases and contains structures such as ribosomes,
a chromosome, and plasmids[2]. The single chromosome is localized in a region
called the nucleoid. Plasmids are small genetic structures made up of circular pieces of DNA. Ribosomes of Bacteria are smaller than Eukaryotic
Ribosomes. They translate the genetic code from the molecular language of the
nucleic acids to that of amino acids and assist in the production of proteins.
Some bacteria also have additional structures, such
as pili (short, hairlike projections) that help them adhere to surfaces and
flagella (long, whip-like appendages) that help them move. Some bacteria also
have specialized structures called spores, which allow them to survive harsh
conditions.
Pili of bacteria:-
Many bacterial species have pili which are small hair-like
projections. These outgrowths aid in the attachment of Bacteria to other cells and
surfaces. Without these structures, bacteria lose the ability to infect because
they are unable to attach to host tissue.
There are several types of pili, including:
Fimbriae: Fimbriae are thin, finger-like projections that are found on the surface
of many bacteria. They are used for adhesion and are involved in the attachment
of bacteria to host cells or tissues.
Sex pili: Sex pili are specialized pili that are involved in the transfer of
genetic material between bacteria during conjugation. They are found on the
surface of certain bacteria and are used to "mate" with other
bacteria, transferring a piece of DNA called a plasmid from one bacterium to
another.
Flagella: Flagella are long, whip-like appendages that are used by bacteria for
motility. They are found on the surface of some bacteria and are used to propel
the bacterium through a liquid medium.
Pili are important for the survival and reproduction of many
bacteria, and they have been the subject of much research due to their
potential role in the development of bacterial infections.
Also, read
list of antibacterial drugs || classification and dose ||
Classification of bacteria:-
Classify bacteria on the bases of cell structure:-
Bacteria
are classified into two main groups based on their cell structure:
gram-positive and gram-negative. The classification is based on the reaction of
their cell walls to a staining technique called the Gram stain, developed by the Danish bacteriologist Hans Christian Gram in 1884.
Gram-positive bacteria have a thick
peptidoglycan layer in their cell wall, which causes them to retain the crystal
violet stain used in the Gram stain and appear purple or blue. Examples include
Staphylococcus and Streptococcus species.
Gram-negative bacteria have a thinner
peptidoglycan layer, as well as an outer membrane containing
lipopolysaccharides (LPS)[1]. This outer membrane causes gram-negative bacteria to
lose the crystal violet stain and instead take up a counterstain, safranin,
which causes them to appear pink or red. Examples include Escherichia coli and
Salmonella species.
Also, read
Difference between Viruses, Bacteria, and Fungi ||
Classify bacteria on the bases of their nutritional characteristics.
These
include:
·
Autotrophic bacteria: These bacteria can produce their own food through processes such as photosynthesis or
chemosynthesis. Examples include cyanobacteria and purple sulfur bacteria.
·
Heterotrophic bacteria: These bacteria are
unable to produce their own food and instead obtain it by consuming organic
matter. Examples include E. coli and Streptococcus.
Classify bacteria on the bases of oxygen requirement:-
· Facultative anaerobic bacteria: These bacteria can grow
in the presence or absence of oxygen. Examples include E. coli and
Staphylococcus aureus.
·
Aerobic bacteria: These bacteria require
oxygen for growth. Examples include Pseudomonas aeruginosa and Streptococcus
pneumonia.
·
Obligate anaerobic bacteria: These bacteria cannot
grow in the presence of oxygen and require an oxygen-free environment. Examples
include Clostridium perfringens and Bacteroides fragilis.
Classify bacteria on the bases of the formation of spores:-
Spores are structures that allow bacteria to survive in adverse
conditions, such as high temperatures, high salt concentrations, or low
moisture. There are two main types of bacteria based on their ability to form
spores:
·
Sporulating bacteria: These bacteria can form spores, which are usually highly resistant to environmental stressors.
Examples include Bacillus and Clostridium species.
·
Nonsporulating bacteria: These bacteria are unable
to form spores and are considered more sensitive to environmental stressors.
Examples include E. coli and Staphylococcus aureus.
Note; It's important to note
that not all bacteria that can form spores are pathogenic, and the ability to
form spores is not exclusive to pathogenic bacteria. Additionally, the
classification of bacteria based on the ability to form spores can be helpful in
determining their survival strategies, as well as in identifying them.
Isoniazid 300mg tablets , uses,
Bacteria can also be classified by their shape:-
which
include:
· Cocci (spherical shaped)
· Bacilli (rod-shaped)
· Spirilla (spiral shaped)
·
Cocci: These bacteria are spherical in shape and
can be found in clusters, pairs, or chains. Examples include Staphylococcus and
Streptococcus species.
structure of cocci |
·
Bacilli: These bacteria are rod-shaped and can be
found individually or in chains. Examples include E. coli and Bacillus species.
structure of Bacilli |
·
Spirilla: These bacteria are spiral-shaped and can
have a variety of forms, such as helical, curved, or hooked. Examples include
Vibrio and Spirochaetes species.
Structure of spirilla |
·
Filamentous bacteria: These bacteria are long
and thread-like, and can be found in clusters or as single cells. Examples
include some species of Actinomycetes and Nocardia.
It's important to note
that the shape of a bacterium can be influenced by the growth conditions, and a
single species of bacteria can have different forms under different
conditions. Additionally, the shape of a bacterium can also be useful in
identifying it and determining its properties such as motility, metabolic
pathways, and pathogenicity.
Bacteria are classified based on their motility
Bacteria can also be classified based on their motility, which refers to their ability to move. The
main types of motility in bacteria are:
·
Motile: These bacteria can move
using flagella, pili, or other appendages. Examples include E. coli and
Salmonella species.
·
Nonmotile: These bacteria cannot
move and are considered sessile. Examples include Streptococcus and
Staphylococcus species.
Note; It is important to note
that the classification based on motility is not absolute and some bacteria may
show different motility depending on the growth conditions. Motility can also be useful in identifying a bacteria and determining its
properties such as pathogenicity.
All of these classifications provide important information about
the biology and behavior of bacteria and can help in identifying and
understanding different bacterial species.
References:-
people search about ;
2 ..Facts need knowing about Black fungus disease (mucormycosis)||
0 Comments