Transcript Mode of living in Bacteria

Mode of living in Bacteria
Considering the oxygen demands of bacteria, it can be classified into:
1. 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.
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.
I: Autotrophic Bacteria
• The autotrophs can be divided into two types:
I: Photoautotrophs
II: Chemoautotrophs.
Autotrophic Bacteria
A. 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
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.
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.
II. Heterotrophic Bacteria
Heterotrophs live either as
Parasites
on
plants, animals
and
humans
causing serious
diseases.
Saprophytes
on
dead organic matter.
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.