Category: Biology Second Paper

Classification on the basis of flagella

The number and distribution of flagella in bacterial cells is called flagellation. Based on the presence, absence, number and location of flagella, bacteria can be classified into following groups.
1. Atricus: Bacteria cells that do not have any flagella are called Atricus. For example- Bacillus diptheriae, Lactobacillus, Pasteurella, Corynebacterium diptheriae.
2. Monotrichous: Bacteria that have only one flagellum at one end of the cell are called monotrichous. For example, Vibrio cholerae.
3. Amphitrichous: Bacteria that have one flagella at both ends of the cell are called Amphitrichous. For example- Nitrosomonas, Spirillum.
4. Cephalotrichus: Bacteria that have a cluster of flagella at one end of the cell is called Cephalotrichus. For example, Pseudomonas aenoginosa, Pseudomonas fluorescens
5. Lophotrichous: Those bacteria that have a total of two sets of flagella at both ends of the cell are called Lophotrichous. For example- Spirillum minus, Pseudomonas.
6. Peritrichous: Bacteria whose entire cell is covered by flagella is called peritrichous. For example- Bacillus typhi, Escherichia coli, Salmonella typhi.

Classification on the basis of dye uptake

Scientist Hans Christian Gram (1853-1938) invented the dyeing method. In this method bacteria are divided into two groups.
1. Gram positive bacteria: Those bacteria that retain the dye (blue, purple) when washed with crystal violet dye are called gram positive bacteria. Their cell walls are thick. Its cell wall consists of peptidoglycan, teichoic acid and thin lipopolysaccharide. Such as Clostridium, Staphylococcus, Streptococcus, Bacillus, Actinobacteria.
2. Gram negative bacteria: Those bacteria which cannot retain the dye after washing with crystal violet dye are called gram negative bacteria. Their cell walls are thin. Its cell wall consists of peptidoglycan and thick lipopolysaccharide. E. coli, Salmonella typhi, Shigella, Proteus, Rhizobium, Vibrio cholerae, Neisseria meningitidis, Cyanobacteria.

Classification on the basis of heat tolerance

Bacteria can be divided into three groups based on heat tolerance.
1. Psychrophilic: Bacteria that survive at low temperature are called Psychrophilic bacteria. All these bacteria can survive at or below zero temperature. A temperature of 25-300C is best for their best growth. For example- Psychrobacter, Acinetobacter, Arthrobacter, Pseudomonas.
2. Mesophilic: Bacteria that survive at normal temperature are called Mesophilic bacteria. A temperature of 30-40 0C is best for their best growth. Such as Azotobacter, Rhizobium.
3. Thermophilic: Bacteria that survive at high temperatures are called thermophilic bacteria. A temperature of 45-600C is best for their best growth. For example – Thermus aquaticus, Bacillus coagulans.