4) Oxidative/Fermentative Test: 
                     During the process of metabolism ie breakdown of complex organic molecules, certain amount of energy is released . Most mos have the capability of catabolizing carbohydrates . Both the extracellular & intracellular enzymes are necessary for the degradation of carbohydrates . Extracellular enzymes degrade complex carbohydrate into simpler carbohydrate which can pass to the cell. The intracellular enzymes catabolize these simpler molecules to generate energy. The end product of this degradation is used in glycolysis for the generation of energy.
  Glycolysis is one of the metabolic pathway in which simple sugar is converted in a form of energy as ATP. If the glucose after entering a cell is catabolized aerobically the process is called oxidative metabolism where oxygen serves as final electron acceptor. If glucose is catabolized anaerobically, the fermentative metabolism takes place where organic molecules serve as final electron acceptor. The end products of carbohydrate fermentation can be either be the organic acids like lactic, formic or acetic or organic gases like hydrogen or carbon dioxide. 

Whether an organism is oxidative or fermentative can be determined by using Hugh & Leifson's Media(O/F Medium). In this method two tubes are used, one open to air & the other sealed with paraffin to create anaerobic condition. By utilizing glucose results in production of acid which changes the color of medium to yellow. Change in color of medium to yellow in both tubes suggests fermentation  while only in open tube suggests oxidation. Certain mos do not use glucose  but instead utilizes nitrogen source, here tryptone. In such case, the medium changes to blue color due to the production of alkaline end products. 

Please visit these links for references: › Science › Biology › Microbiology

Cited BY Kamal Singh Khadka 
Assistant Professor in PU, RE-COST, PNC, LA, NA


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