What are the different ways of the classification of bacteria?

Bacteria may be classified using many different classification systems. 

1. Based on the cell wall:

• Peptidoglycan cell wall – Gram-positive bacteria
• Lipopolysaccharide cell wall – Gram-negative bacteria

2. Based on shape:

• Coccus – Unicellular, spherical shaped, remaining as a single cell or aggregating together in various configurations
• Bacillus - Rod-shaped or cylindrical, remaining singly or in pairs
• Spirilla or spirochete – Spiral with multiple curvatures in its structure and terminal flagella
• Vibrio - Comma-shaped or curved and represented by a single genus

3. Based on mode of respiration:

• Aerobic – Break down glucose molecules completely in the presence of oxygen to yield energy
• Anaerobic – Break down glucose partially in the absence of oxygen to yield reduced energy

4. Based on mode of nutrition:

• Phototrophs – Gain energy from light
• Autotrophs – Obtains carbon only from carbon dioxide to prepare its own food 
• Heterotrophs – Source carbon from organic compounds
• Chemotrophs – Gain energy from chemical compounds

5. Based on number of flagella: 

• Atrichos – No flagella
• Monotrichous – One flagellum attached at one end of the cell
• Lophotrichous – Multiple flagella attached at one end of the cell
• Amphitrichous – Multiple flagella attached to both ends of the cell
• Peritrichous – Flagella evenly distributed around and covering the entire cell

6. Based on optimum temperature for growth: 

• Psychrophiles –15 °C or below
• Psychotrophs – 20°C to 30°C
• Mesophiles - 37°C
• Thermophiles – Above 45°C
• Hyperthermophiles – Above 80°C

7. Based on optimum pH requirements for growth: 

• Acidophiles – Acidic pH
• Alkaliphiles – Alkaline pH
• Neutrophiles – Neutral pH 6.5 to 7.5