Variety of Living Organisms » Prokaryotic Organisms - Bacteria

What you'll learn this session

Study time: 30 minutes

The structure and characteristics of bacteria as prokaryotic organisms
How bacteria reproduce through binary fission
The different shapes and arrangements of bacterial cells
The role of bacteria in disease and beneficial applications
How bacteria adapt to their environments
Key differences between prokaryotic and eukaryotic cells

Introduction to Prokaryotic Organisms - Bacteria

Bacteria are tiny but mighty! These microscopic organisms are found virtually everywhere on Earth - from the deepest ocean trenches to the insides of our bodies. Despite their small size (most are only 1-5 micrometres long), bacteria play crucial roles in ecosystems, human health and many industrial processes.

Key Definitions:

Prokaryote: An organism whose cells lack a true nucleus and membrane-bound organelles.
Bacteria: Single-celled prokaryotic microorganisms that typically have cell walls and reproduce by binary fission.
Binary fission: The asexual reproduction process where a bacterial cell divides into two identical daughter cells.
Pathogen: A bacterium, virus, or other microorganism that can cause disease.

🔬 Bacterial Cell Structure

Bacteria are prokaryotic cells with these key features:

No nucleus - genetic material (DNA) floats freely in the cytoplasm as a circular chromosome
Cell wall - made of peptidoglycan, provides structure and protection
Plasma membrane - controls what enters and leaves the cell
Cytoplasm - gel-like substance where chemical reactions occur
Ribosomes - where proteins are made (smaller than in eukaryotes)
Plasmids - small circular DNA molecules separate from the main chromosome
Some have flagella - whip-like structures for movement

🧬 Prokaryotic vs Eukaryotic

Understanding how bacteria differ from eukaryotic cells:

Size: Prokaryotes are typically 10 times smaller
DNA: Not enclosed in a nucleus in prokaryotes
Organelles: Prokaryotes lack membrane-bound organelles
Reproduction: Prokaryotes reproduce by binary fission, not mitosis
Complexity: Prokaryotes have simpler cellular organisation
Ribosomes: Smaller (70S) in prokaryotes compared to eukaryotes (80S)

Bacterial Shapes and Arrangements

Bacteria come in different shapes and arrangements, which help scientists identify and classify them. The three main shapes are:

🥜 Bacilli

Rod-shaped bacteria

Examples: Escherichia coli (E. coli), Bacillus subtilis

Can occur singly or in chains called streptobacilli

⚪ Cocci

Spherical bacteria

Examples: Staphylococcus aureus, Streptococcus pneumoniae

Can form pairs (diplococci), chains (streptococci), or clusters (staphylococci)

🌀 Spirilla

Spiral-shaped bacteria

Examples: Treponema pallidum (causes syphilis), Helicobacter pylori

Can be rigid spirals or flexible coils called spirochetes

Bacterial Reproduction

Bacteria reproduce asexually through a process called binary fission. This allows them to multiply rapidly when conditions are favourable.

Binary Fission Process

Binary fission is a simple but effective way for bacteria to reproduce:

The bacterial DNA (chromosome) replicates
The cell grows larger
The cell membrane pinches inward at the centre
A new cell wall forms between the two DNA copies
The cell splits into two identical daughter cells

Under ideal conditions, some bacteria can divide every 20 minutes! This means one bacterium could theoretically produce millions of offspring in just a few hours. This rapid reproduction explains why bacterial infections can develop so quickly and why food can spoil so fast.

Case Study Focus: Antibiotic Resistance

The rapid reproduction rate of bacteria contributes to the growing problem of antibiotic resistance. When bacteria are exposed to antibiotics, most die, but some may have mutations that allow them to survive. These surviving bacteria reproduce, passing on their resistance genes. This is why it's important to complete antibiotic courses as prescribed - to ensure all bacteria are killed and prevent the development of resistant strains.

MRSA (Methicillin-resistant Staphylococcus aureus) is a well-known example of an antibiotic-resistant bacterium that causes difficult-to-treat infections in hospitals and the community.

Bacterial Adaptations

Bacteria have evolved various adaptations that help them survive in different environments:

🛡️ Survival Mechanisms

Endospores: Some bacteria like Bacillus and Clostridium can form tough protective spores when conditions are unfavourable. These can survive extreme heat, cold, drying and chemicals.
Capsules: Slimy protective layers that help bacteria avoid being engulfed by white blood cells.
Flagella: Whip-like structures that allow bacteria to move toward nutrients or away from harmful substances.
Pili: Hair-like structures that help bacteria attach to surfaces or connect to other bacteria during genetic exchange.

🔄 Genetic Adaptability

Bacteria can adapt genetically through:

Mutations: Random changes in DNA that may provide advantages.
Conjugation: Transfer of genetic material between bacteria through direct contact.
Transformation: Uptake of DNA from the environment.
Transduction: Transfer of DNA via bacteriophages (viruses that infect bacteria).

These mechanisms allow bacteria to share beneficial genes, such as those for antibiotic resistance, rapidly throughout populations.

Bacteria in Disease and Health

While some bacteria cause disease, many are harmless or even beneficial to humans and other organisms.

🦠 Pathogenic Bacteria

Disease-causing bacteria can harm us through:

Toxin production: Chemicals that damage cells and tissues (e.g., Clostridium botulinum produces botulinum toxin)
Direct invasion: Bacteria multiply within tissues causing damage (e.g., Streptococcus pneumoniae in pneumonia)
Triggering inflammation: The body's immune response to infection can cause symptoms like fever and swelling

Examples of bacterial diseases:

Tuberculosis (Mycobacterium tuberculosis)
Food poisoning (Salmonella, E. coli)
Cholera (Vibrio cholerae)
Tetanus (Clostridium tetani)

👍 Beneficial Bacteria

Many bacteria are helpful or essential:

Gut microbiota: Bacteria in our digestive system help break down food, produce vitamins and protect against harmful microbes
Nitrogen fixation: Bacteria like Rhizobium convert atmospheric nitrogen into forms plants can use
Decomposition: Bacteria break down dead organisms, recycling nutrients in ecosystems
Food production: Used to make yogurt, cheese, sauerkraut and other fermented foods
Antibiotics: Many antibiotics are produced by bacteria to kill competing microbes
Biotechnology: Bacteria are used to produce insulin, enzymes and other useful products

Interesting Fact: Bacteria Outnumber Us!

Did you know that the human body contains about 30 trillion human cells but hosts approximately 39 trillion bacterial cells? That means there are more bacterial cells in your body than human cells! Most of these bacteria live in your gut and on your skin, forming complex communities that help keep you healthy. Scientists call this collection of microorganisms your "microbiome," and research suggests it plays important roles in digestion, immunity and even mental health.

Practical Applications

Understanding bacteria has led to many practical applications in medicine, agriculture and industry:

Genetic engineering: Bacteria like E. coli are used as "factories" to produce human insulin, growth hormone and other medicines
Bioremediation: Using bacteria to clean up pollution and oil spills
Probiotics: Beneficial bacteria in supplements and foods that promote gut health
Biological control: Using bacteria like Bacillus thuringiensis (Bt) as natural pesticides
Food preservation: Understanding bacterial growth helps develop methods to keep food safe

As we continue to learn more about bacteria, we discover new ways they can help solve human problems, from creating biodegradable plastics to developing new antibiotics.

🧠 Test Your Knowledge!