Glossary of Terms

Control of Microbial Growth

Sterilization. The killing or removal of all microorganisms.

Disinfection. The killing, inhibition, or removal of pathogenic microorganisms from objects or surfaces. Disinfection does not always sterilize.

Sanitization. The reduction of microbial populations to levels considered safe by public health standards. This usually involves partial disinfection.

Antisepsis. The killing or removal of microorganisms/pathogens from living tissue.

Antibiotic. A compound produced by a microorganisms that is used to treat an infection (usually bacterial) in living tissue.

D-value: The amount of time it takes to kill 90% of the target population

Thermal Death Point: The temperature required to kill all microorganisms in 10 minutes.

Thermal Death Time: The time it takes to kill al microorganisms at a given temperature.


Metabolism: The sum total of all biochemical reactions that an organism carries out

Anabolism: The sum of all build-up reactions (biosynthesis, polymerization, assembly). Requires energy and/or reducing power. Includes Calvin cycle.

Catabolism: The sum of all breakdown reactions. Releases energy, reducing power, intermediates/building blocks and/or waste products. Catabolism includes Hydrolysis reactions, glycolysis, pentose phosphate pathway, Entner-Doudoroff pathway, Krebs cycle, beta oxidation.

Autotroph: Organism that uses CO2 as its main source of carbon. Autotrophs assemble CO2 into organic molecules using the Calvin cycle (for example)

Heterotroph: Organism that requires pre-formed organic chemicals as its source of carbon. Hence, it uses catabolic pathways s.a. glycolysis and Krebs cycle to process these organic compounds

Phototroph: Organism that obtains its energy from light. Requires photosynthetic pigments and a photosynthetic electron transport chain. Many phototrophs are also autotrophs.

Chemotroph: Organism that obtains its energy from chemical compounds (organic or inorganic). Those that use organic chemicals are known as chemoheterotrophs and use catabolis pathways s.a. glycolysis and Krebs cycle. Those that use inorganic chemicals are known as chemoautotrophs (aka lithotrophs) and assemble their precursor molecules using the Calvin cycle.

Lithotroph: Organism that obtains its reducing power (electrons/H) from inorganic sources s.a. water (photolithotrophs) or reduced inorganic compounds (H2S, NH4)

Organotroph: Organism that uses organic compounds as its source of reducing. power. Includes all chemoheterotrophs and some phototrophs.

Mixotroph: Organism that can switch from using light to using chemicals as its energy source. Example: Euglena

ATP: The cell's primary energy currency. ATP yields energy when it is hydrolyzed to ADP + Pi. Enzymes that do this are called ATPases. The energy released by this hydrolysis can be used to drive chemical reactions, transport reactions, or motion.

Reducing power: Compounds that can transfer electrons/Hydrogens to other compounds. The cell's primary currency for reducing power are the coenzymes NAD+, NADP+ and FAD.

Reduction: When a compound gains electrons, it is reduced. Frequently, electrons are accompanied by protons (H+).  A reduction has occurred if a) a compound has gained H, b) a compound has lost O, or c) if the net charge (all other things being equal) has become more negative

Oxidation: When a compound has lost electrons, it has become oxidized. Frequently, this involves the gain of Oxygen atoms which 'compensate' for the lost electrons by electron sharing.

Glycolysis: The chemical pathway that breaks down glucose to 2 pyruvate, resulting in the net gain of 2 ATP and 2 NADH for the cell. ATP is gained by substrate-level phosphorylation. Note that, with the gain of 2 NADH, 4 electrons have been lost from glucose (i.e. pyruvate is an oxidized molecule).

Entner-Doudoroff pathway: An alternate chemical pathway to break down glucose to 2 pyruvate. Since this pathway is less efficient, less energy (1 ATP) is gained than in glycolysis. Yields 1 NADH + 1 NADPH

Pentose phosphate pathway: A third pathway that can catabolize glucose to pyruvate. The primary purpose of this pathway, however, is the production of ribose and erythrose sugars. These precursors can only be found in this pathway. The pentose phosphate pathway uses 1 ATP. Yields 2 NADPH.

Krebs cycle: Catabolic pathway that breaks down pyruvate to acetyl CoA (2-carbon fragments) + 2 CO2 + 2 NADH, then adding acetyl groups to oxaloacetate (4 carbons). The resulting citrate (6 carbons) is then broken down to oxaloacetate, producing 3 NADH, 1 FADH2, 1 GTP, and 2 CO2 in the process. Since this pathway generates large quantities of reducing power, an electron transport chain is required to process the NADH and FADH2. This pathway is used in respiration but not in fermentation.

Respiration: Metabolic process that requires an electron transport chain. Electrons are usually transferred to inorganic electron acceptors such as oxygen or nitrate. Respiratory electron transport chains are found in chemoheterotrophs and chemolithotrophs.

Aerobic respiration: The catabolism of compounds and generation of energy using oxygen as the final electron acceptor. Most chemolithotrophs and aerobic chemoheterotrophs require this pathway.

Anaerobic respiration: The electron transport chain of some microbes can use compounds other than oxygen as the final electron acceptos. Examples include nitrate, nitrite, sulfate, sulfur, carbon dioxide, iron (Fe3+). The end product of this process is the reduced form of the electron acceptor (e.g. nitrite, ammonium, N2 gas, sulfur, sulfite, H2S gas, methane, or iron (Fe2+).

Fermentation: Metabolic pathway where organic molecules are the final electron acceptors. Usually, pyruvate or one of its metabolites is reduced. Occurs in the absence of oxygen. Products include ethanol, acetic acid, lactic acid, propionic acid, butyric acid, carbon dioxide, hydrogen gas, or formic acid.