Archaebacteria and its Details
- The cells that have different characters from both prokaryotes and eukaryotes are called as Archaebacteria.
- The microorganisms that are placed in Archaebacteria group are prokaryotic in nature but are closely related to the eukaryotic bacteria.
- Archaebacteria are heterogenous bacteria found in extreme habitat like
1. High Temperature
2. High Salt concentration
3. Low pH
4. High pH
- It is considered extreme conditions were present during early development of the earth and these archaebacteria were present at that time so these bacteria are called as primitive bacteria.
- Archaebacteria are considered as original ancestors of prokaryotic and Eukaryotic bacteria. So These bacteria are called as extremophiles.
Important Characters of Archaebacteria
- The genome of Archaebacteria is similar to eubacteria. The genome is circular closed DNA molecule but contains low DNA content that is less number of a base pair as compared to the Eukaryotic cell.
- The cell type of Archaebacteria is of the prokaryotic type in nature.
- Membrane-bound organelles are absent.
- The ribosome is of 70S type.
- The 70S ribosome is sensitive to diphtheria toxin. Hence the translation process can be inhibited by Diphtheria toxin.
- The carbon dioxide fixation is not carried out by Calvin cycle.
- The base pair sequence of 30S ribosome of 16SrRNA is different as compared to eukaryotic bacteria.
- The cell wall of Archaebacteria contains protein and polysaccharides so called as pseudomurein.
- Peptidoglycan is absent in cell wall of Archaebacteria so they are resistant to antibiotics like penicillin and cephalosporin.
- The cell wall of Archaebacteria is made up of lipid molecules and these lipid molecules are made up of long chain of hydrocarbons like phytanyl.
- These hydrocarbon molecules are linked to each other by glycerol molecules.
- The protein synthesis of archaebacteria is resistant to the action of antibiotics like chloramphenicol and streptomycin.
1] Methanogenic Bacteria
- Methanogenic bacteria have a capability to produce methane biologically.
- They are anaerobic in nature and strictly sensitive to oxygen.
- Methanogenic bacteria can gram positive or gram negative in nature.
- They may be mesophilic or thermophilic in nature.
- Their shape may vary from rod, cocci and filamentous in shape.
- There are basically four group of methanogenic bacteria and they are Group I, Group II, Group III and Group IV.
- Methanogenic bacteria may be flagellated or non- flagellated in nature.
- The methanogenic bacteria may be present in Swamp mud, Bottom sediments of oceans, lakes as well as digestive systems of animals.
- Methane is produced by methanogenic bacteria. Methane can be used as a fuel as well as it can control greenhouse effect and it helps in avoiding global warming effect.
- Examples – Methanobacterium, Methanospirullum, Methanococcus and Methanosarcina.
2] Red Extremophilic Bacteria
- Red Extremophilic bacteria are the bacteria the bacteria that require high salt concentration for their growth.
- These bacteria are present in the extremely saline environment like salt lakes, solar salt evaporating plants and heavily salted meat or fish.
- These are simply halophilic bacteria that require high salt concentration.
- There are two genres of halophilic bacteria and that are Halococcus and Halobacterium.
- The cytoplasmic region has high salt concentration so all intracellular biomolecules are salt tolerant as well as the require saturation level of salt for their proper functioning. Extremophilic bacteria contain red carotenoid pigment in the cell membrane so they appear red in colour.
- Halophilic bacteria are non-motile, non-spore forming and Gram-negative in nature.
- They are organotrophic and obligate anaerobic in nature. Very few species are able to grow anaerobically in nature.
- Some strains carry out photophosphorylation for generation of ATP molecule.
- The cell wall of Halobacterium contains acidic glycoprotein.
- Whereas the cell wall of Halococcus is made up of Sulphate heteropolysaccharide.
3] Thermoacidophile bacteria
- They are facultative, anaerobic and chemosynthetic in nature.
- It is a heterogeneous group of bacteria that have the ability to grow in high temperature and low pH.
- They are Gram-negative bacteria found in hot Sulphur springs.
- In aerobic condition, they oxidize Sulphur to Sulphur dioxide and in the anaerobic condition, they reduce Sulphur to Hydrogen sulphide.
- There are three types of thermophilic bacteria and they are
- Present in hot spring and hot soil.
- Spherical and lobate in shape.
- Optimum pH is 2 and can grow in pH range of 1 to 5.9.
- Temperature range for growth is 55 to 80 degree Celsius.
- They use elemental Sulphur as a substrate to produce sulphuric acid as the product.
- The cell wall is made up of carbohydrate and lipoproteins
- It grows at temperature range 37 to 65 degree Celsius.
- Facultative anaerobes
- They are found in piles of burning mines.
- Oxidize iron pyrite and form acid and heat.
- The cell wall is absent.
- The cell membrane is made up of lipopolysaccharides and lipoproteins.
- Thermo proteus can only be isolated from geothermal areas of Iceland.
- They are thin rods of length 80 micrometres.
- Temperature range is 78 to 95 degree Celsius.
- Ph range is 2.5 to 6