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Microbial energetics is defined as the mechanisms by which bacteria and other microbial cells derive the energy they require for growth from their environment. Microbial metabolism is the means by which a microbe obtains the energy and nutrients (e.g. carbon, nitrogen, phosphorus) it needs to live and reproduce. Microbial energetic helps microbiologists to predict the growth yields of microbes. Bacteria can synthesize adenosine triphosphate (ATP) by a variety of routes that includes fermentation, oxidative phosphorylation, and substrate level phosphorylation and possibly by the excretion of metabolic end products from their systems.

An important part of microbial metabolism is microbial energetics. Microbial energetics is driven by Gibbs free-energy yield derived from ATP. ATP is heterotrophically generated by fermentation or respiration. The latter requires terminal electron acceptors (e.g. molecular oxygen, nitrate, sulphate, ferric iron, carbon dioxide, or molecular hydrogen), and produces greater amounts of ATP per unit substrate. Fermentation is less feasible in the presence of either highly oxidized or highly reduced substrate, and may raise toxic products (simple organic acids) that can eventually impede the process of the microbial growth. The energy in soil is preserved in both organic and inorganic components enabling the microbial communities to sustain catabolic and anabolic processes.

Metabolism as aforementioned isdefined as the subtotal of chemical reactions occurring in a living cell. These chemical reactions areenzyme-catalyzed i.e. they are spurred or controlled by the activities of enzymes. Enzymes are protein catalysts that speed up the rate of reaction in a living system. The different types of metabolism via which microbes synthesis or utilize molecules in their environment are (1) Anabolism (anabolic process) and (2) Catabolism (catabolic process). Anabolic process (anabolism) is defined as the metabolic process in which complex molecules from simpler molecules with the input of energy.

Anabolism is an energy requiring process i.e. it uses energy to build up complex molecules. The synthesis of protein (a complex molecule) from simpler molecules such as amino acids is an example of an anabolic process. Catabolic process (catabolism) is defined as the metabolic process in which complex molecules are broken down to simpler molecules with the release of energy. The energy released by the cell during catabolism is used by the organism to do work.   

Further reading

Jee C and Shagufta (2007). Environmental Biotechnology. APH Publishing Corporation, Darya Ganj, New Delhi, India.

Latha C.D.S and Rao D.B (2007). Microbial Biotechnology. First edition. Discovery Publishing House (DPH), Darya Ganj, New Delhi, India.

Maier R.M, Pepper I.L. and Gerba C.P (2000). Environmental Microbiology. Academic Press, San Diego.

Mishra B.B, Nanda D.R and Dave S.R (2009). Environmental Microbiology. First edition. APH Publishing Corporation, Ansari Road, Darya Ganj, New Delhi, India.

Paul E.A (2007). Soil Microbiology, ecology and biochemistry. 3rd edition. Oxford: Elsevier Publications, New York.

Pelczar M.J., Chan E.C.S. and Krieg N.R. (2003). Microbiology of Soil.  Microbiology, 5th Edition. Tata McGraw-Hill Publishing Company Limited, New Delhi, India.

Pepper I.L and Gerba C.P (2005). Environmental Microbiology: A Laboratory Manual. Second Edition. Elsevier Academic Press, New York, USA. 

Roberto P. Anitori (2012). Extremophiles: Microbiology and Biotechnology. First edition. Caister Academic Press, Norfolk, England.

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