Powering Through: Fermentation in Bacteria

If aerobic respiration is more energy-efficient than fermentation, then a facultative bacterium will prioritize using oxygen. If oxygen is present, then the rate of glucose consumption actually slows down because more energy is gained per molecule.

If a metabolic pathway is a sequence of chemical reactions catalyzed by specific enzymes, then missing one "step" prevents the final product. If the final step to ethanol requires alcohol dehydrogenase, then the pathway is blocked without it.

If Clostridium bacteria infect deep tissue where oxygen is low, then they will perform fermentation. If their specific fermentation pathway releases CO2 and hydrogen gas, then gas bubbles will build up in the infected tissue.

If the word "facultative" means having the ability to live under more than one specific set of environmental conditions, then these flexible bacteria can adapt to the presence or absence of oxygen.

If the fermentation process results in molecules like lactic acid, acetic acid, or formic acid, then the concentration of hydrogen ions in the environment will increase. If hydrogen ions increase, then the pH level must decrease.

If bacteria have diverse metabolic pathways, then some perform "homolactic" fermentation (only lactic acid) while others perform "heterolactic" or "mixed-acid" fermentation. Therefore, the byproducts vary by species.

If the fermentation steps themselves produce zero ATP and only serve to recycle NAD+, then the only energy gained is from the preceding glycolysis. If glycolysis has a net yield of 2 ATP, then that is the total for the process.

If glycolysis requires NAD+ to produce energy but converts it all into NADH, then the process will stall. If fermentation in bacteria converts NADH back into NAD+, then glycolysis can continue to produce a small amount of ATP.

If the chemical reaction for alcoholic fermentation involves removing a carboxyl group from pyruvate, then a gas molecule must be released. If that molecule is CO2, then it causes the bubbling seen in fermenting liquids.

If humans use bacteria to sour and thicken milk, then they need a species that produces high amounts of acid. If Lactobacillus converts lactose into lactic acid, then it is the primary organism used in dairy production.

If aerobic respiration produces up to 32 ATP per glucose and fermentation only produces 2 ATP from glycolysis, then fermentation is significantly less efficient at extracting energy.

If NADH must be oxidized back to NAD+, then it must donate its electrons to another molecule. If the cell reduces pyruvate directly to form lactic acid, then pyruvate is the final electron acceptor.

If a cell begins breaking down glucose, then it starts with the universal pathway of glycolysis. If oxygen is absent, then the cell must follow this with fermentation to handle the resulting pyruvate.

If bacteria are prokaryotes, then they lack membrane-bound organelles like mitochondria. If metabolic pathways must occur without these organelles, then they must take place in the cytoplasm.

If an organism's enzymes are damaged by oxygen, then it is an obligate anaerobe. If it lacks oxygen-processing tools, then it must rely on fermentation and live in shielded areas like the digestive tract.

If an environment lacks oxygen, then aerobic respiration is impossible. If a cell has the genetic instructions for fermentation, then it can still generate energy and survive without air.

If a pH indicator turns yellow in the presence of acid, and if the bacteria are given sugar in a closed tube, then a color change proves that fermentation occurred and released acid.

If different bacterial species possess different enzymes, then they will produce different waste products. If they ferment, they can produce acids, alcohols, and gases; however, they consume glucose rather than producing it.

If fermentation is an anaerobic alternative to the Krebs cycle, then pyruvate will not enter the mitochondria/Krebs cycle. If it is used to recycle NAD+, then it is reduced into waste products like ethanol or acid within the cytoplasm.

If we use bacterial acids for preservation or alcohols for fuel, then fermentation is the key. If we observe which sugars a germ ferments to identify it, then we are using the process for medical diagnosis.