- Bacteria (singular bacterium) are unicellular microorganism which are of microscopic size and cannot be seen with unaided eyes.
- Constitute large domain-prokaryotes.
- They are among the first life form evolve on the earth and present in most of the habitat.
- Bacteria inhabit normal to the extreme habitat like air, water, soil, radioactive waste, hot springs, deep seas, even in human gut, etc.
- Also live in symbiotic and parasitic relationship with plants and animals. Example rhizobium associate with leguminous plants.
- Length of bacteria ranges in few micrometres. E.coli (1.0-2.0 micrometre long and 0.5 micrometre in radius), Mycobacterium tuberculosis (2-4 micrometre long and 0.2-0.5 micrometre width), V cholerae (1-3 micrometre long and 0.5-0.8 micrometre radius).
- The study of this discipline of microbiology is called bacteriology.
- Bacteria are beneficial for human and other animals in a way that they produce various kind of vitamins, enzyme and food products. Example- vitamin B12, lactic acid, alcohol.
- They are key components of our biosphere playing important role in biogeochemical cycles, removal of toxic substance and decomposition of waste materials.
- Involve in nitrogen fixation hence improve soil fertility.
- With beneficial characteristics several bacteria are pathogenic and cause various kind of disease in human, plants and animals. Example- cholera, tuberculosis, syphilis, anthrax, and more.
- In industries bacteria are useful in waste water treatment and industrial fermentation for cheese and yogurt production.
- Bacteria is a prokaryotic organism their body lacks nucleus and cellular components.
- Bacteria are covered by a membrane called cell wall chiefly made up peptidoglycan (murein layer).
- Peptidoglycan layer mainly constitute of polysaccharide which are cross linked by peptide bonds.
- Peptidoglycan layer is made up of two glucose derivative N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) chain. The chain is linked with tertapeptide bonds
- Four protein in tetrapeptide bond are L-alanine, D-alanine, L-lysine or meso-diaminopimelic acid (DPA) and D-glutamine.
- Cell wall contributes to the survival of the bacteria, protection from harsh environment and antibiotics.
- Peptidoglycan layer in gram positive bacteria is 20-80 nm thick in contrast gran negative bacteria contain 2-7 nm thick layer.
- Gram negative bacteria contain acidic substance known as teichoic acids which provide rigidity to the cell wall.
- Over the cell wall gram negative bacterium contain an external layer called outer membrane it contain lipopolysaccharide, phospholipids, lipoprotein and proteins.
- It’s the carbohydrate enriched layer that covers the outside of the bacteria.
- It provides protection against host
- This glycocalyx layer associate with the pathogenic property to the bacteria.
- Glycoclayx in a tightly packed form is called as capsule, in contrast in loose packing it is called as slime layer.
- Hairlike structure, attach on the surface of the cell, main function is to provide mobility to the bacteria
- Both gram positive and gram negative bacteria contain flagella. Consist of three parts filament, hook and basal body.
- Thin hairlike structure on the surface of gram negative bacteria
- Play an Important role in conjugation process
- Present on both kind of cells gram negative an gran positive
- Helps in attachment to the surface
|Bacillus (Rod-Shaped)||Escherichia coli (E. coli)|
|Coccus (Sphere)||Streptococcus pneumoniae|
|Vibrio (Comma Shaped)||Vibrio cholerae|
|Spirilla or spirochete (Spiral)||Spirillum volutans|
- Mode of Nutrition
|Autotrophic Bacteria||Purple bacteria|
|Heterotrophic Bacteria||All disease-causing bacteria|
- Cell Wall
|Gram positive||Staphylococcus aureus|
- Mode of Respiration
- The mode of replication in bacterium is binary fission.
- In this process the parent bacterial cell divided into two identical daughter cells.
- Replication of DNA starts in the parent cell and each copy is transfer into the daughter cell.
- Rate of reproduction is depend on the conditions like temperature, nutrient availability, moisture this is called favourable condition. E.coli generation rate is 2 million bacteria in 7 hrs.
- In some rare cases they undergo sexual reproduction by conjugation, transduction and transformation. Helps in genetic modification in bacteria which results in the antibiotic resistant property.