Life processes in Bacteria
Two types of respiration is found in Bacteria. They
are 1. Aerobic respiration 2. Anaerobic respiration.
These bacteria require oxygen as terminal acceptor
and will not grow under anaerobic conditions (i.e. in the absence of O2)
Example: Streptococcus.
Some Micrococcus
species are obligate aerobes (i.e.
they must have oxygen to survive).
These bacteria do not use oxygen for growth and
metabolism but obtain their energy from fermentation reactions. Example: Clostridium.
There are bacteria that can grow either using
oxygen as a terminal electron acceptor or anaerobically using fermentation
reaction to obtain energy. When a facultative anaerobe such as E. coli is present at a site of
infection like an abdominal abscess, it can rapidly consume all available O2
and change to anaerobic metabolism producing an anaerobic environment and thus
allow the anaerobic bacteria that are present to grow and cause disease.
Example: Escherichia
coli and Salmonella.
Bacteria which require CO2 for their
growth are called as capnophilic bacteria. Example: Campylobacter.
On the basis of their mode of nutrition bacteria
are classified into two types namely Autotrophs and Heterotrophs.
Bacteria which can synthesis their own food are
called autotrophic bacteria. They may be further subdivided as
Bacteria use sunlight as their source of energy to
synthesize food. They may be
In Photolithotrophs the hydrogen donor is an
inorganic substance.
a. Green
sulphur bacteria: In this type of
bacteria the hydrogen donor is H2S and possess pigment called Bacterioviridin. Example: Chlorobium.
b. Purple
sulphur bacteria: For bacteria
belong to this group the hydrogen donor is Thiosulphate, Bacteriochlorophyll is present. Chlorophyll containing chlorosomes
are present Example: Chromatium.
They utilize organic acid or alcohol as hydrogen
donor. Example: Purple non sulphur bacteria – Rhodospirillum.
They do not have photosynthetic pigment hence they
cannot use sunlight energy. This type of bacteria obtain energy from organic or
inorganic substance.
This type of bacteria oxidize inorganic compound to
release energy.
Examples:
1. Sulphur
bacteria Thiobacillus thiooxidans
2. Iron
bacteria Ferrobacillus ferrooxidans
3. Hydrogen
bacteria Hydrogenomonas
4. Nitrifying
bacteria Nitrosomonas and Nitrobacter
This type of bacteria oxidize organic compounds to
release energy.
Examples:
1. Methane
bacteria – Methanococcus
2. Acetic
acid bacteria – Acetobacter
3. Lactic
acid bacteria – Lactobacillus
They are Parasites (Clostridium, Mycobacterium)
Saprophytes (Bacillus mycoides) or
Symbiotic (Rhizobium in root nodules of leguminous crops).
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