Introduction
Today, bacteria are considered one of the oldest forms of life on Earth. Although most bacteria are known for causing diseases, they have long-term, mutual relationships with humans and play a crucial role in our survival.
But before we dive into their uses, let’s first understand the structure of bacteria, their classification, and diagrams in detail.
Definition of Bacteria
Bacteria are unicellular organisms belonging to the prokaryotic group, where some organelles and a true nucleus are absent.
Bacteria Diagram
The diagram below represents the structure of a typical bacterial cell, showing parts like the cell wall, plasmid, cytoplasm, and flagella clearly labeled.
Ultrastructure of a Bacterial Cell
Bacteria are known for their simple physical design. They are unicellular microorganisms lacking a nucleus and other organelles, so they are classified as prokaryotes.
They are also highly versatile and can survive even in extreme environments. Such organisms are called extremophiles, and they are classified into different types based on their habitat:
- Thermophiles – Heat-loving
- Acidophiles – Acid-loving
- Alkaliphiles – Base-loving
- Osmophiles – High-sugar-concentration-loving
- Barophiles – Pressure-loving
- Cryophiles – Cold-loving
Another fascinating feature of bacteria is their protective cell wall, made of a unique protein called peptidoglycan. This component is a key basis for bacterial classification, and this protein is not found elsewhere in nature.
Some bacteria lack this wall, and others have a third protective layer called a capsule. On the outer surface, they may have one or more flagella or pili—flagella aid in movement, and pili help some bacteria attach to host cells.
Except for ribosomes, they lack organelles found in plant or animal cells. Ribosomes are the sites for protein synthesis. In addition to DNA, they may contain an extra circular DNA called a plasmid, which can make some strains resistant to antibiotics.
Classification of Bacteria
Bacteria are classified based on their characteristics and properties. The main classification is based on:
- Shape
- Cell wall composition
- Mode of respiration
- Mode of nutrition
Classification Based on Shape
| Type | Example |
|---|---|
| Bacillus (Rod-shaped) | Escherichia coli (E. coli) |
| Spirilla or Spirochete (Spiral-shaped) | Spirillum volutans |
| Coccus (Spherical) | Streptococcus pneumoniae |
| Vibrio (Comma-shaped) | Vibrio cholerae |
Classification Based on Cell Wall Composition
| Type | Example |
|---|---|
| Peptidoglycan cell wall | Gram-positive bacteria |
| Lipopolysaccharide cell wall | Gram-negative bacteria |
Classification Based on Nutrition
| Type | Example |
|---|---|
| Autotrophic bacteria | Cyanobacteria |
| Heterotrophic bacteria | All pathogenic (disease-causing) bacteria |
Classification Based on Respiration
| Type | Example |
|---|---|
| Anaerobic bacteria | Actinomyces |
| Aerobic bacteria | Mycobacterium |
Reproduction in Bacteria
Bacteria reproduce asexually through a process called binary fission, where one bacterium divides into two identical daughter cells. The process starts with DNA replication, followed by the elongation of the cell and its division into two.
The rate of reproduction depends on conditions like time, temperature, and nutrient availability. Under optimal conditions, E. coli can produce around 2 million bacteria every 7 hours.
Although bacterial reproduction is entirely asexual, in rare cases, genetic recombination can occur through:
- Conjugation
- Transformation
- Transduction
These processes allow genetic variation, which may lead to antibiotic resistance—unlike standard asexual reproduction, where identical genetic material is passed down.
Useful Bacteria
Not all bacteria are harmful to humans. Some bacteria are highly beneficial in various ways. Here are a few advantages:
- Curd Formation – Lactobacillus or lactic acid bacteria
- Fermented Food Products – Streptococcus and Bacillus species
- Aid in digestion and improve immunity – Actinobacteria, Bacteroidetes, Firmicutes, Proteobacteria
- Antibiotic Production – Soil bacteria produce antibiotics that help treat and prevent bacterial infections
Harmful Bacteria
Some bacteria are responsible for various diseases, such as:
- Pneumonia
- Tuberculosis (TB)
- Diphtheria
- Syphilis
- Tooth decay, and many other infectious diseases.
These effects can be treated using antibiotics and prescribed medications.
However, prevention is better than cure. Sterilizing exposed surfaces, tools, equipment, and utilities can eliminate most disease-causing bacteria. Common sterilization methods include:
- Heat
- Disinfectants
- UV radiation
- Pasteurization
- Boiling
Read Also: Human Metapneumovirus (hMPV)