Mode of living in Bacteria

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Mode of living in Bacteria

• Considering the oxygen demands of bacteria, it
  can be classified into

• Aerobes.
• They require free supply of oxygen.

• 2. Anaerobes
• They grow in complete absence of oxygen.

• 3. Facultative aerobes
• They can live either in presence or absence of
  oxygen.

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Mode of living in Bacteria

• If we consider the mode of nutrition, bacteria
  can be divided into two categories
• 1. Autotrophs. They can build up complex organic
  substances such as carbohydrates from simple
  inorganic sources (CO2 and water).
• 2. Heterotrophs. They cannot build up
  carbohydrates from simple inorganic sources. They
  depend on ready made organic materials derived
  from plants , animals of humans. They can live on
  such compounds , break it down , enzymatically ,
  into simpler compounds which can be absorbed. The
  process of break down of such complex organic
  substances releases energy which can be used by
  such bacteria in building up its complex
  protoplasmic material from the simple absorbed
  substances.

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I Autotrophic Bacteria

• The autotrophs can be divided into two types
• I Photoautotrophs II
  Chemoautotrophs.

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Autotrophic Bacteria

• Photoautotrophs.
• They contain in their cells a chlorophyll
  known as bacterial chlorophyll by which they can
  perform photosynthesis. Here, the energy used in
  building up processes is derived from light. As
  an example of such bacteria is the green sulphur
  bacteria.
• Light Energy
• 6CO2 12 H2S
  C6H12O6 6 H2O 12 S
• Green sulphur bacteria

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Autotrophic Bacteria

• B. Chemoautotrophs. Here the cells lack
  chlorophll. Accordingly the source of energy
  should be something else than light. The energy
  used here is released from chemical reactions
  carried out by such bacteria. Most of such
  reactions are oxidative.

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Autotrophic Bacteria (Chemoautotrophs)

• Three examples we have
• 1) Nitrosomonas, oxidizes ammonia or ammonium
  salts to nitrites with a release of energy
• 2NH3 3O2
  2 HNO2 2H2o Energy
• 2) Nitrobacter, oxidizes nitrites to nitrates
  with a release of energy
• 2HNO2 O2
  2 HNO3 Energy
• 3)Thiobacillus thiooxidans, oxidizes sulphur with
  a release of energy
• 2S 3O2 2H2O
  2 H2SO4 Energy
• The energy released from any of these oxidation
  reactions is utilized by the specific organism in
  building up organic carbohydrates from the simple
  inorganic sources, CO2 and water.

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II. Heterotrophic Bacteria

• Heterotrophs live either as

Saprophytes on dead organic matter.
Parasites on plants, animals and humans causing
serious diseases.
Symbionts with other living organisms sharing
benefit, e.g. Rhizobium (nodule bacteria)
which lives in symbiosis with the roots of
legumes forming root nodules. It can fix
nitrogen and build proteins and other nitrogenous
compounds to be partially delivered, to the
higher plant and get in return the carbohydrates
from the latter.