Freshwater sample extracted from
a pond is taken into a glass cylinder. As it is made of glass, light is able to
penetrate through it. It is kept for few weeks further observations. After few
weeks, a mud layer deposit at the bottom of the cylinder. As a result of
microbial activities, separation of layers in the water column can be seen.
At
the beginning, aerobic respiratory organisms are taken place. They consume the
large amount of organic matter present in the bottom mud layer. As they use
oxygen as their terminal electron acceptor in their electro transport chains,
oxygen in the mud layer is depleted. Then fermentative microorganisms become
active. Clostridium is the one of
fermentative bacteria that is active in the mud under anaerobic conditions.
They use as cellulose as their substrate and produce alcohols, acids and
aldehydes as their byproducts. After that anaerobic microorganisms are active.
They use fermentative byproducts as their substrate in the anaerobic
respirations. They use sulfate as their terminal electron acceptor in their
electro transport chains. So they convert sulfate ions into hydrogen sulfide. Hydrogen
sulfide reacts with iron (II) in the mud. As a result of this reaction ferrous
sulfide is produced. It gives a black to the mud. Since Hydrogen sulfide is
gas, it moves upward of the water column.
Green
sulfur bacteria live in the layer just above the mud. They are shown in green
color due to the color of photosynthetic pigments. The method of ATP synthase of them is
photosynthesis. As the light penetrates through the water column, they are able
to do photosynthesis. They use hydrogen sulfide as their electro donor to
fulfill the electro deficiency in the chlorophyll. So oxidation of hydrogen
sulfide give an electron the chlorophyll and convert into sulfur. Sulfur is deposited in their cells. Reaming hydrogen
sulfide moves further upward.
Purple
sulfur bacteria live in the layer just above the green sulfur bacteria. They
are unable to live in bottom area where the concentration of hydrogen sulfide
is high. because high concentration of hydrogen sulfide are toxic and able to
kill them. They are shown in purple color due the color of their photosynthetic
pigments. Their method of ATP synthase is photosynthesis and use hydrogen
sulfide as their electron donor in chlorophyll. Oxidation of hydrogen sulfide
fills the electron deficiency in chlorophyll and converts into sulfur. Sulfur
deposit in their cells. Reaming hydrogen
sulfide reaches to the surface layer.
In
the surface layer of the water column, oxygen is highly available. Therefore
Aerobic respiratory microorganisms are abundant there. So sulfur oxidizing
bacteria like Thiobacillus thioxidans
live there. They are also called as Chemolithropic organism those who use
oxidation of inorganic substrate to synthesis ATP. They use hydrogen sulfide as
their substrate and produce ATP. The
oxidation of hydrogen sulfide gives electrons to run an electron chain so hydrogen
sulfide is converted into sulfate ions. Sulfate ions are highly soluble in the
water. Dissolved sulfate ions come to
the bottom mud layer. Again Sulfate is
used as terminal electron acceptor by anaerobic respiratory microorganisms and
release hydrogen sulfide.
Therefore
all the activities taken place in the water column are interrelated. Product or byproducts of a reaction become
substrate of electron donor or terminal electron acceptor of other reactions.
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