📚 Classification of Bacteria (According to Margulis and Schwartz)
Two scientists — Margulis and Schwartz — created a classification system that divided all prokaryotes into 16 phyla (large groups). Let’s learn about some important bacterial groups in detail.
1. 🧫 Omnibacteria
- Shape: Rod-shaped and rigid (not flexible).
- Gram-negative: This refers to the type of cell wall they have — it doesn’t retain the violet stain in Gram staining.
- Nutrition: Heterotrophic — they cannot make their own food and get it from other organisms.
- Movement: Most have flagella (tail-like structures used for swimming).
- Spores: They don’t form spores.
- Oxygen: They usually require oxygen (aerobic).
- Examples:
- Escherichia coli (E. coli) — found in the intestines, some strains can cause food poisoning.
- Vibrios — another type in this group, some cause cholera.
2. 🌱 Cyanobacteria (Blue-Green Algae)
These are very special bacteria because:
- They photosynthesize, like plants.
- They contain pigments like chlorophyll-a (green), carotenoids (orange), and phycobilins (blue and red).
✅ Important functions:
- They helped increase the oxygen level in Earth’s early atmosphere — which made life possible for other organisms.
- They can fix nitrogen (turn nitrogen gas from the air into useful nitrogen compounds) using special cells called heterocysts.
📍 Where are they found?
- In soil (as mats)
- On rocks (as part of lichens)
- In oceans and lakes (marine sediments)
3. 🚫 Mycoplasmas and Spiroplasmas
- These are unique because they don’t have cell walls.
→ That’s why antibiotics like penicillin don’t work on them (penicillin targets cell walls).
✅ Diseases:
- Mycoplasma can cause pneumonia in humans.
- Spiroplasma can cause plant diseases, like lethal yellowing in coconuts.
4. 🔄 Spirochaetes
- Shape: Long, spiral-shaped bacteria.
- Gram-negative: Thin cell wall structure.
- They have many flagella (2 to over 100!) which help them move in a twisting motion.
- Example: Treponema, which causes syphilis — a dangerous sexually transmitted disease.
5. 🌊 Pseudomonads
- Shape: Straight or curved rods.
- Gram-negative, with one or more flagella at one end.
- Habitat: Found in soil and water.
- Can break down many types of organic material (useful in cleaning polluted environments).
✅ Some are:
- Plant pathogens (cause diseases in plants).
- Involved in denitrification — converting nitrates into nitrogen gas.
- Example: Pseudomonas aeruginosa
→ Can infect people with weak immune systems, and is found in soil, water, and even raw vegetables.
6. 🧵 Actinomycetes
- These bacteria grow in a filamentous form (like threads or branches).
- They produce spores that resist dryness and extreme conditions.
✅ Functions:
- Some live in root nodules and fix nitrogen.
- Some cause dental problems like plaque (destroy tooth enamel).
- Others cause diseases like:
- Leprosy (by Mycobacterium leprae)
- Tuberculosis (by Mycobacterium tuberculosis)
💊 Important fact:
Many antibiotics (like tetracycline, erythromycin, and neomycin) come from actinomycetes.
7. 🌿 Nitrogen-fixing Aerobic Bacteria
- These bacteria need oxygen (aerobic) and have flagella.
- They live in soil or water and convert nitrogen gas (N₂) into nitrates (NO₃⁻) — a form that plants can use to grow.
✅ Example: Azotobacter
This process is very important for agriculture, as it naturally fertilizes soil.
8. ⚗️ Chemosynthetic Bacteria
- These bacteria don’t use sunlight like plants.
- Instead, they get energy by oxidizing (chemically changing) inorganic compounds like:
- Nitrogen compounds
- Sulphur compounds
- Iron compounds
They use this energy to make their own food (chemosynthesis).
✅ Examples:
- Nitrosomonas and Nitrobacter — both help convert ammonia (NH₃) into nitrates, which is a key step in the nitrogen cycle.