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Definition:
Bacteria is defined as the organism with only one cell and is hence known as unicellular. It lives both inside and outside the living organisms. Most of the bacteria are beneficial and play a vital role in the ecosystem. One often used example of bacteria is E.coli (Escherichia coli).
Bacterial classification in five kingdom classification:
R. H. Whittaker proposed the five kingdom classification in the year of 1969. He classified all the living organisms into five major kingdoms namely Monera, Protista, Fungi, Plantae and Animalia. The bacteria is classified into the kingdom of Monera. The kingdom Monera comprises the unicellular organisms or the prokaryotes. They lack true nucleus and cell organelles that are bound by the membrane. While the other kingdoms in the five kingdom classification consist only of eukaryotes or multicellular organisms. The kingdom Monera comprises both the eubacteria and archaebacteria.
● Eubacteria:
They are known as the true bacteria since they have a cell wall made of peptidoglycan compared to the other type. They have only single cells without a nucleus but with a single stranded circular DNA. A few eubacteria make their own food, some depend on dead matters and living organisms. Examples of eubacteria include Staphylococcus, Lactobacillus, E.coli and Salmonella.
● Archaebacteria:
A few years ago, they were classified under the category of bacteria. But, recently they are skipped from the bacterial classification as they possess different chemical and biochemical mechanisms unlike bacteria. They survive in extreme environments Some of the examples include thermoproteota and nitrososphaeria.
Types of bacteria:
The bacteria are classified into different types based on their structure of cell wall, nutrition mode, oxygen requirements and its shape.
● Structure of cell wall:
The bacteria is classified into two major types namely, gram-positive and gram-negative bacteria based on their components of cell wall.
1. Gram positive bacteria:
They have a very thick peptidoglycan layer in the cell wall and are made of teichoic acid. They get into the color of purple or blue and appear crystal violet color after gram staining.
2. Gram negative bacteria:
They have a thin peptidoglycan layer in the cell wall and Lipopolysaccharide (LPS) is present. They retain the pink color after gram staining.
● Nutrition mode:
The bacteria is classified into four major types based on their mode of nutrition. They are autotrophs, heterotrophs, phototrophs and chemotrophs.
● Autotrophs:
These organisms produce food on their own from the substances that are inorganic.
● Heterotrophs:
These organisms have their food from organic matter.
● Phototrophs:
These organisms acquire energy from the source of light.
● Chemotrophs:
These organisms acquire energy from certain chemical reactions.
● Oxygen requirements:
The bacteria is classified into three different types based on the intake of the oxygen by them. They are facultative aerobes, aerobes and anaerobes.
● Facultative aerobes:
These organisms can grow in the presence as well as the absence of oxygen.
● Aerobes:
These organisms essentially need oxygen for their growth.
● Anaerobes:
These organisms grow in the absence of oxygen.
● Shape:
The bacteria is classified into three major types based on their shape. They are coccus, spirillum and bacillus.
● Coccus:
These organisms are oval or spherical in shape.
● Spirillum:
These organisms are helical or spiral shaped.
● Bacillus:
These organisms are rod shaped.
Bacterial reproduction:
Bacteria undergoes reproduction by two major ways namely, sexual and asexual reproduction.
● Sexual reproduction:
The bacteria undergoes the process of reproduction sexually by transformation, conjugation and transduction.
● Transformation:
It is the process, where the bacteria forms the new cell by the uptake of the exogenous DNA from the environment.
● Conjugation:
Here, the genetic material is transferred from one bacteria to another by means of physical contact known as pili or conjugation tube. Usually, the plasmid is the genetic material that is transferred.
● Transduction:
In this process, the genetic material is carried by the bacteriophage (a virus which infects bacteria) from one bacteria to another.
● Asexual reproduction:
The bacteria undergoes the process of reproduction asexually by budding, binary fission, endospore formation, conidia formation and cyst formation.
● Budding:
A bud forms in the bacteria and it grows naturally, then gets split down from the parent.
● Binary fission:
The DNA is replicated and the bacterial cell divides into two, forming new cells.
● Endospore formation:
The formation of endospore occurs in the extreme environmental conditions such as scarcity of nutrients, drought etc.,
● Conidia formation:
The structures called conidia develop at the filament ends and they germinate into new cells in the suitable conditions.
● Cyst formation:
The bacteria develops into a cyst of all the extra layers and the cyst forms a new bacterial cell, when the environmental conditions return to normal.
Benefits of bacterial species:
The bacteria is helpful in various fields which include maintaining a healthy gut, preventing a disease and supporting the immune system in humans. It is also useful in the industrial applications such as producing food, biogas, medicine and crops and as well as in bioremediation and biotechnology. The environmental benefits of bacteria include purification of water, cycling of nutrients and health of the soil.
Harmful effects of bacteria:
Some of the harmful effects of bacteria include material damage, food spoilage, food poisoning and soil fertility reductions. Bacteria can also cause infectious diseases in plants and animals.
● Infectious diseases:
It can cause skin infections such as impetigo, cellulitis and erysipelas, respiratory infections such as pneumonia, gastrointestinal diseases such as digestive issues, diarrhea and food poisoning and human diseases such as dysentery, diphtheria, typhoid, tuberculosis and many more.
Antibiotic resistant bacteria:
Certain bacteria's are resistant to antibiotics by self mutating their genetic material, acquiring resistant properties naturally and by means of horizontal gene transfer. The mechanisms involved in antibiotic resistance include inactivation of drugs, decrease in the uptake of drugs, efflux pumps and modifications of the target.
The consequences associated with the property of antibiotic resistance include impossibility or severity in treating a disease, organisms prone to death and threat to modern medicine. These disadvantages can be overcome by practising good hygiene and using antibiotics only when it is necessary.
