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
A. Photoautotrophic bacteria
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.
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.
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).