Microorganisms play an important role in biogeochemical cycles such as the carbon and oxygen cycles. The carbon cycle involves the exchange of carbon between the biosphere, geosphere, hydrosphere, and atmosphere. Microbes are responsible for decomposing organic matter into carbon dioxide through aerobic and anaerobic respiration. Different groups of microbes cycle carbon under aerobic and anaerobic conditions through processes like photosynthesis, methane production, and carbon monoxide oxidation. The oxygen cycle similarly involves microbes that use oxygen during respiration and cyanobacteria that produce oxygen through photosynthesis, maintaining an equilibrium between oxygen production and consumption on Earth.

1. SOIL MICROBIOLOGY -
BIOGEOCHEMICAL CYCLE OF
CARBON
Dr. S. Anu Kiruthika
Bengaluru North University
Bengaluru.
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2. INTRODUCTION
 Water is the source of oxygen, and the aerobic atmosphere of Earth is produced by
continuous photosynthetic processes.
 When O 2 production initially occurred on Earth, there were no aerobic organisms and
molecular oxygen accumulated.
 A robust collection of biological systems evolved to consume O 2 through respiration, and
currently there is equilibrium between O 2 production and O 2 consumption.
 When compared to other elements, the oxygen cycle is relatively simple.
 Large numbers of microorganisms interface with the oxygen cycle through redox
reactions.
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3. OXYGEN CYCLE
 Solid lines indicate reduction; dashed lines indicate
oxidation.
 Heterotrophic and chemolithotrophic
microorganisms associated with the use of oxygen as
the terminal electron acceptor.
 Cyanobacteria were associated with the
photosynthetic release of molecular oxygen from water.
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4.  There is an interconnection between the oxygen and carbon cycles
because oxygen reserves are found in organic compounds and CO2.
 With carbon as a principal element in cell systems, it would follow that
distribution,fluxes, and reserves of carbon would be of global interest.
 Microorganisms have an important role in all aspects of the carbon
cycle.
 Primary producers are the organisms that fix carbon dioxide, and while
higher plants are important in terrestrial areas, algae and cyanobacteria
account for primary productivity in marine environments.
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5.  Nonphotosynthetic fixation of carbon dioxide by chemolithotrophic or
heterotrophic bacteria accounts for relatively small amounts of carbon
transferred from the atmosphere to biomass.
 Large quantities of carbon are dissolved in ocean water as
bicarbonate ion (HCO3-), and comparable quantities of primary
productivity occur in marine and terrestrial systems.
 Different groups of microorganisms are used for the cycling of C
under aerobic and anaerobic conditions.
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6. CARBON CYCLE
 Carbon is exchanged among the biosphere, geosphere, hydrosphere and atmosphere of the
earth.
 Carbon is actively cycled between inorganic CO2 and the variety of organic compounds that
compose living organisms and their dead organic matter.
 Among the step of carbon cycle decomposition of organic matter by microbes is very important.
 Decomposition of organic matter in soils is done by fungi along with other microbes, chiefly
bacteria.
 Decomposition help to release nutrient blocked up in the dead organic matter of plants and
animals.
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7.  In soil, microbes oxidize organic carbon into Co2 and liberate bound materials.
 Several types of decomposers are present.
 Cellulose decomposers – cellulose decomposing fungi mainly include Ascomycetes and
Deuteromycetes eg. Apergillus, Penicilium, Trichoderma, Fusarium etc.
 They break down cellulose simple sugar.
 Lignin decomposers – decomposed by Bascideomycetes such as Aphyllophorales & Agaricales
decomposition done by the production of lignolytic enzymes.
 Besides fungi, bacteria are also involved in the decomposition.
 Pectin decomposers – pectin substance are breakdown by microbial pectinase.
 Pectinase are produced by various specious of Rhizopus, Aspergillus, Fusarium and Geotrichum etc.
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8. Microbial metabolism of carbon under anaerobic and aerobic conditions
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11.  Soil is a great reservoir for carbon with appreciable quantities of complex organic material
known as humus is stable with a very low turnover rate.
 Although carbon dioxide is released from plants and animals by respiration, great quantities
of carbon dioxide result from decomposition of organic matter by microorganisms.
 Methane is produced by anaerobic archaea, and the resulting methane hydrates produced
may account for a considerable percentage of total carbon on Earth.
 Oxidation of methane with production of carbon dioxide is attributed to aerobic bacteria.
 Carbon monoxide is produced by a few bacteria as a result of decomposition, and this gas
does not become toxic because aerobic bacteria readily oxidize carbon monoxide to carbon
dioxide.
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15. THE END
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