Kingdom Monera- 2 | Additional Study Material for NEET PDF Download

Archaebacteria

"Group of ancient bacteria"

• They are primitive organisms. They were the first to be born on our planet and they are present even today with their primitive characters. They are the"Oldest living fossils".
• They are different from eubacteria in many ways.
  
  Archaebacteria
• All archaebacteria are obligate anaerobes.
• Thermococcus, Methanococcus and Methanobacterium exemplify archaebacteria that contain proteins homologous to eukaryotic core histones.
• Their cell wall is not made up of peptidoglycan like that of eubacteria. Their cell wall is made up of complex polysaccharides and polypeptide.
• Their cell membrane is not a unit membrane, while in eubacteria, the cell membrane is a unit membrane.
  Eubacteria

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• In archaebacteria sequence of nucleotide in 16S – r RNA is different from other prokaryotes.

➢ Archaebacteria include the following Bacteria

1. Methanogens

 "Methane producing bacteria"

• These bacteria convert CO₂ of swampy areas (Marshy) into methane (CH₄).
  Example: Methanobacterium, Methanococcus, Methanomicrobium
• These bacteria convert the organic substance (cellulose) present in cow dung into methane by fermentation (Gobar gas fermenter).
  Example: Methanobacterium, Methanococcus, Methanomicrobium
• An archaebacterium is found in cattle's rumen, where it digests the cellulose by fermentation and converts it into methane.
  Example: Ruminococcus

Ruminococcus

2. Halophiles

• These archaebacteria are found in highly saline areas.
  Example: Halobacterium
  Halophiles- Halobacterium
• Halococcus Halophiles are surrounded by a purple membrane. This membrane absorbs the bright light and directly forms ATP i.e. they cannot prepare food (carbohydrates) like eubacteria. Instead, they directly produce ATP.
• Therefore, Halophiles are non-photosynthetic.

3. Thermo Acidophiles

• These archaebacteria are found at places where the temperature is approx 80°C and the medium is acidic [pH = 2].
• They are found in hot sulphur springs. These can also survive at 100°C temperature.
• They oxidise sulphur to H₂SO₄ and obtain energy. This is used to prepare food. Due to the conversion of sulphur to H₂SO_4, the medium (water) becomes acidic in nature.
• These are chemoautotrophs.
• Hot water sulphur springs are found in the Himalayan region.
• Exceptionally these archaebacteria are facultative aerobes.
  Example: Thermus, Sulpholobus, Thermoplasma

Eubacteria

• Eubacteria are also known as “true bacteria”.
• The cell wall is rigid and made up of peptidoglycans.
• It moves with the help of flagella.
• A few bacteria contain short appendages on the cell surface, known as pili which help the bacteria during sexual reproduction. Pili also helps a pathogen to attach to the host.
• They are divided into two categories; gram-positive and gram-negative, depending upon the nature of the cell wall and the stain they take.
• Rhizobium and Clostridium are two eubacteria.

Rickettsia

• They are also called as bacteria because they are similar to eubacteria in structure.
• These are intracellular endoparasite.
• These are non-motile.
  Rickettsia

• Diseases caused by rickettsia in humans:
  (i) Typhus fever: Rickettsia prowazekii 
  (ii) Rocky Mountain spotted fever: R. rickettsii 

Chlamydia

• The chlamydiae are a group of microbes classified as a type of rickettsiae. They also have the characteristics of rickettsiae, like very small in size, having both DNA & RNA and a number of enzymes.
• They can be treated with some antibiotics.
• They are obligate intracellular energy parasites of animals. They form the elementary body, initial body or reticulate body, during their reproductive cycle. They divide by binary fission.
  Example: Chlamydia trachomatis, C.psittaci

Disease caused by chlamydia are:
(i) Trachoma (eye disease)
(ii) Non-gonococcal urethritis (reproductive system disease)
(iii) Chlamydial ophthalmia

Myxobacteria

• They are gram –ve coccus like or rod-shaped bacteria, having mucilage on their cell wall, so they form slimy colonies and are usually called as swarm stage or pseudoplasmodium.
• They multiply by transverse binary fission and form non-motile fruiting bodies called cysts or microcysts or myxospores.

Myxobacteria

• They do not form flagella, pili and endospores. They are bacteriolytic and cellulolytic.
• Some myxobacteria show gliding movement.
  Example: Myxococcus, Cystobacter, Flexibacter, Stigmatella