Monera contain two groups of bacteria. One is archaebacteria and other is Eubacteria. Evolutionary Eubacteria are more developed. Eubacteria are more advanced than archaebacteria and can live everywhere on Earth, except in the most extreme archaebacterial environments. All bacterial illnesses are caused by eubacteria.
Structure Of Eubacteria
Bacterial cell has a chemically complex cell envelope. The cell envelope consists of a tightly bound three layered structure. Outermost glycocalyx, cell wall and cell membrane. Although each layer of the envelope performs distinct function they act together as a single protective unit.
Loose and thin layer is slime layer and thick and tough layer is capsule. When bacteria are surrounded by capsule, called as capsulated bacteria. Formation of capsule is done by cell membrane. Capsulated bacteria are mostly pathogenic. Capsule is made up of polysaccharides and polypeptides while slime layer is made up of only polysaccharides. Glycocalyx protects the bacteria from WBC and also helps in colony formation.
Bacterial cell wall is made up of mainly peptidoglycan or murein which is a type of muco-peptide.
Bacterial cell membrane is made up of lipoprotein like the eukaryotic membrane.
Types of Eubacteria
- Cyanobacteria have chlorophyll (similar to green plants) and are photosynthetic autotrophs.
- Cyanobacteria were the first organisms that produced O2 on our earth and also known as BGA.
- The cyanobacteria are unicellular (Spirullina), colonial (Anabaena) or filamentous (Oscillatoria).
- They may be freshwater or marine or terrestrial algae.
- The cytoplasm of prokaryotes lacks membrane bound cell organelles but exceptionally in BGA two membrarne bound structure are present: Gas vacuole and thylakoids. Gas vacuole provides the buoyancy to the BGA in water. Thylakoids contain photosynthetic pigments.
- The colonies are generally surrounded by gelatinous sheath.
- They often form blooms in polluted water bodies. Excessive growth of BGA in water, that pollute the water is knwon as water bloom.
- Some of BGA can perform Nitrogen fixation. They converts atmospheric nitrogen in to nitrogenous compound like amino acids, nitrates.
- BGA fix nitrogen in two forms: Symbiotic form and Free living form.
- Some of these organisms can fix atmospheric nitrogen in specialised cell called heterocysts. Example: Nostoc and Anabaena.
- Heterocysts is thick walled, non green cell.
- Cyanobacteria contain special type of gene nif-gene (Nitrogenase inducing factor). It stimulates the production of nitrogenase enzyme. Nitrogenase is necessory for nitrogen fixation.
- These are nonphotosynthetic autotrophs. They use chemical energy instead of light energy for food synthesis. Chemical energy is obtained from oxidation of chemical compounds.
- Bacteria oxidise various inorganic substances such as nitrates, nitrites and ammonia and use the released energy for their ATP production.
- They play a great role in recycling nutrients like nitrogen, phosphorous, iron and sulphur.
- These are the most abundant in nature.
- The majority are important decomposers.
- Many of them have a significant impact on human affairs. They are helpful in making curd from milk, production of antibiotics, fixing nitrogen in legume roots, etc.
- Some are pathogens causing damage to human being, crops, farm animals and pets. Cholera diseases caused by different bacteria.
- Some of bacteria use light energy for food synthesis. But this photosynthesis is non oxygenic.
- Photolysis of water does not take place here, so hydrogen is received from other sources like inorganic sulphur compounds (H2S) or organic compound (Amino acids, Fatty acid etc.)
- Example: Sulphur producing bacteria.
- Mycoplasma are organisms that completely lack a cell wall.
- These are the smallest living cells known and can survive without oxygen.
- Many mycoplasma are pathogenic in animals and plants.
Reproduction In Bacteria
Bacteria reproduce by two methods: Asexual and Genetic Recombination.
Asexual reproduction takes place by binary fission and by endospore.
It is similar to sexual reproduction but it is not true sexual reproduction. Because it does not involve fusion of male and female gametes to produce a diploid zygote. Genetic recombination involves transfer of some genes from a bacterium to another bacterium. There are two methods of genetic recombination: Transformation and Conjugation.