- Archaebacteria and Eubacteria are the 2 major groups of Monerans. Bacteria and Cyanobacteria are the two types of Eubacteria. Mycoplasma, rickettsiae and actinomycetes are some other groups of Monerans.
- Basically, they are unicellular with Peptidoglycan cell wall containing 10S ribosomes, which multiply through binary fission.
- Bacterial cells are of many types on the basis of shape
(i) Coccus – Spherical / ovoid
(ii) Bacillus – Cylindrical / rod
(iii) Spirillum – Cork-screw
(iv) Vibrio – Comma
(v) Stalked / budding
- Based on the reaction of bacteria to Gram’s stain, bacteria can be grouped into either Gram (+) or Gram (−ve). Gram (+ve) bacteria retain blue (or) purple colour. Gram (−ve) bacteria retain safranin.
- The various form of flagellation in bacteria are as follows
(i) Atrichous – Flagella absent
(ii) Monotrichous – Single flagellum
(iii) Amphitrichous – Flagellum at each end
(iv) Lophotrichous – A group of Flagella at one end
(v) Peritrichous – Flagella distributed all over the body
(vi) Cephalotrichous – A tuft of flagella at each ends.
- Bacteria has its outermost covering part as cell envelope that contains 3 components glycocalyx, cell wall and cell membrane
- Glycocalyx if occurs as a loose sheath, will be called a slime layer. But if it is thick and tough, the layer is called a capsule.
- The cell wall of gram-negative bacteria is 2 layered with 20-30% lipid content that occurs in a wavy format.
- Gram (−ve) bacteria contain LPS (Lipopolysaccharide) which gives resistance to it against antibiotics and are harmful than Gram (+ ve)
- Gram (+ve) bacteria have a single-layered cell wall with no outer membrane.
- Gram (+ve) bacteria do not contain LPS but they possess teichoic acid (forms surface antigens)
- Peptidoglycan cell wall layer possesses the repeated units of NAG (N-Acetyl Glucosamine) and NAM (N- Acetyl Muramic acid), cross-linked with small peptide chains.
- Exception: In Mycobacterium and Nocardia, the cell wall possesses mycolic acids, which are long chain fatty acids.
- The plasma membrane is made of Phospholipids that act as a selectively permeable membrane which is metabolically active that plays a role in respiration, lipid synthesis and cell wall synthesis.
- Mesosomes are a villiform specialization of a cell membrane, that is of 2 types: septal and Lateral mesosome.
- Septal mesosome helps in the formation of septum during cell division, whereas lateral mesosome (chondroid) contains respiratory enzymes.
- Ribosomes generally occur in groups called Polysomes which help in translational amplification
- Photoautotrophic bacteria contain chromatophores, which are called chlorosomes in green bacteria.
- The genetic material of prokaryotes is termed as Nucleoid, Incipient nucleus, genophore, Prochromosome (or) chromoneme and it is a circular DNA. It is also called naked as it doesn’t have histone protein.
- Plasmids are extrachromosomal circular DNA (double-stranded) which impart certain phenotype to bacteria (eg. Fertility factor, resistance, etc.,). Sometimes they get associated temporarily with a chromosome called an episome.
- Inclusion bodies are the non-living structures which are of 3 types – (i) Gas vacuoles (ii) Inorganic inclusions and (iii) Food reserve.
- Flagella are uni-stranded with 3 parts – (i) Basal body (ii) Filament and (iii) hook and they are made up of a protein – Flagellin.
- Pili (longer and fewer) made up of pilin helps in the formation of conjugation tube in F + bacteria.
- Fimbriae help in adhesion/attachment of a bacterium and also in mutual clinging of bacteria
- Reproduction in bacteria can be of several methods such as binary fission, sporulation and sexual reproduction. (conjugation that happens between F+/F− bacteria) Where F+ is donor and F− is a recipient.
- On the basis of respiration, bacteria is of 4 types
(i) Obligate aerobes (strict): Bacillus subtilis
(ii) Obligate anaerobes: Clostridium botulinum
(iii) Facultative anaerobes: Halophiles (generally aerobic)
(iv) Facultative aerobes: Rhodopseudomonas (generally anaerobic)
- Photoautotrophic bacteria possess photosynthetic pigments like bacterio-chlorophyll and bacterio-pheophytin, which are anaerobes that do not evolve oxygen during photosynthesis such type is called Anoxygenic photosynthesis (Eg. Purple/green sulphur bacteria).
- Chemoautotrophic bacteria manufacture their organic food from inorganic raw materials. Eg [Sulphur, Iron, Nitrifying bacteria].
- Saprophytic bacteria obtain food from organic remains. [Nature’s scavengers]
- Anaerobic breakdown of carbohydrates and proteins are called Fermentation and Putrefaction respectively.
- Aerobic breakdown of organic compounds is decay.
- Symbiotic bacteria has mutual contact with other organism. Eg. E coli in Human intestine produces Vitamin B and K.
- Parasitic bacteria may or may not cause diseases.
- Toxins produced by them could be endo (Eg. Vibrio Cholerae) / Exotoxins (Eg. Clostridium tetani)
- Archaebacteria (lacks peptidoglycan) contains Pseudomurein, which differ in 16S rRNA nucleotides from those of other organisms.
- They generally live in adverse/extreme environmental conditions.
- Archaebacteria are of 3 major types – (i) Methanogens (ii) Halophiles (iii) Thermoacidophiles.
- Mycoplasma are the minute and the simplest organisms of the procaryotes, that are also called MLO (Mycoplasma like Organisms), PPLO (Pluro pneumonia like organisms) (or) Mollicutes.
- As they lack the cell wall, they are pleomorphic (can change themselves into various shapes).
- Cyanobacteria (Blue green Algae) perform oxygenic photosynthesis, which had evolved 3 billion years ago.
- BGA is autotrophic that mastered all sorts of environment. Even the Red Sea is named after its presence. [Trichodesmium erythraeum]
- It contains a trichome filament with mucilage covering it. Trichome filament can be of homocystous (Oscillatoria) (or) heterocystous (Nostoc) but lacks flagella.
- BGA possess a heterocyst that is impermeable to O2 but permeable to N2 and so it helps in Nitrogen fixation as it also has an enzyme – Nitrogenase.
- Some Cyanobacteria produce toxins. Eg. Microcystis aeruginosa, Anaebaena flos aquae.
View this video for the topic from 0:10 to 13:09
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