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CLASSIFICATION OF BACTERIA

The classification is done based on factors like their shape, nutrition requirement, cell wall staining, the cell appendages etc.

CLASSIFICATION BY CELL WALL TYPE

This bacterial cell wall is made of 3 materials in general viz. carbohydrates, proteins (peptidoglycan) and lipids (lipopolysaccharide). Cell wall of bacteria differs based on the layers in it. Gram stain is used to classify these bacteria based on the variation in the layers.

The grams staining helps in classification of bacteria as gram positive & gram negative bacteria. In gram +ve bacteria there is thicker peptidoglycan layer while gram -ve has less peptido-glycan and more of glycolipid membrane. So, the bacterial species which take up blue color on grams stain is termed gram +ve bacteria. The one which takes up orange color is called gram -ve bacteria.

CLASSIFICATION OF BACTERIA BY SHAPE OR CELL STRUCTURE

CLASSIFICATION OF BACTERIA BASED ON FLAGELLA PRESENCE

Atrichous bacteria: With no flagella on the bacterial cell wall. These are non-motile bacteria

Monotrichous bacteria: with one single flagella.

Amphitrichous bacteria: Two flagella on both sides of cell

Polytrichous bacteria: Many flagella at different points

Lopotrichous bacteria: Flagella at one pole or point of the cell

Flagella around the cell: Peritrichous bacteria. The flagella are present all over the cell wall

CLASSIFICATION OF BACTERIA BASED ON NUTRITION REQUIREMENTS

Autotrophs: These are bacteria which prepare their own food. Due to presence of chlorophyll like pigment they perform photosynthesis. They do this by using sun-light as source of energy. Besides they take up CO2 and water from nature. This photosynthesis helps in formation of carbohydrates. These carbohydrates provide the energy. Example: Chlorella.

Chemoautotrophs: As the name indicates they survive on chemicals. These are bacteria synthesize their own food by use of energy obtained from chemical sources. They differ from autotrophs in that they do not need sunlight.

Heterotrophs: These are bacteria which do not synthesize their own food but obtain it from others they can feed on food materials like animals do.

Symbiotic bacteria: (Sym + Biosis = Living together) these are bacteria which obtain food by living together with other organisms. They reside in mutual beneficial support with others. Example is Entero-bacteria in the intestine. Hence taking too many antibiotics kills the friendly bacteria in out gut causing problems to us.

Saprophytic bacteria: (sapro+phytes = rotten material + plant) these are bacteria survive by eating rotten material. They get their nutrition by consuming dead and decaying material, thus there by help in cleaning the environment from accumulation of waste.

♦ Pathogenic bacteria: (patho+genisis =disease + causing) these are bacteria responsible for diseases in humans and plants. They grow only in the body of other animals or plants. They get their nutrition from the host. In doing so, they consume the vital living elements in them and induce diseases.

CLASSIFICATION BASED ON TEMPERATURE DEPENDENCE

Thermophilic (thermo+phyllic=temperature loving); Thermophylic bacteria are those which can survive at high temperature of 45 to 60 degree temperatures

Mesothermic (medium+thermic= medium temperature) can survive at 25 to 45 degrees

Hypoctermic (hypo = low) these bacteria survive at low temperatures like 8 degree or even less.

CLASSIFICATION BASED ON OXYGEN REQUIREMENT

Not all bacteria require oxygen to survive. Some can survive without oxygen. These are the microbes considered to be immortals due to cell division. But this feature adds even more weight to it. Bacteria are classified based on the oxygen requirement as

Aerobic: Which require oxygen to survive.

Anaerobic bacteria: These bacteria do not require oxygen for survival. They are further as two types

Obligate anaerobes: They survive in absence of oxygen. But when exposed to oxygen they die.

Facultative anaerobes: These also survive in environments without oxygen but when exposed to oxygen they can survive.

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