The Crabtree effect, named after the English biochemist Herbert Grace Crabtree, describes the phenomenon whereby the yeast, ''

Saccharomyces cerevisiae ''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungus microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have been o ...

'', produces

ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...

(alcohol) in aerobic conditions at high external

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...

concentrations rather than producing biomass via the tricarboxylic acid (TCA) cycle, the usual process occurring aerobically in most yeasts e.g. ''

Kluyveromyces ''Kluyveromyces'' is a genus of ascomycetous yeasts in the family Saccharomycetaceae. Some of the species, such as '' K. marxianus'', are the teleomorphs of '' Candida species''. The genus name of ''Kluyveromyces'' is in honour of Albert Jan Klu ...

'' spp. This phenomenon is observed in most species of the ''Saccharomyces'', ''

Schizosaccharomyces ''Schizosaccharomyces'' is a genus of fission yeasts. The most well-studied species is ''S. pombe''. At present five Schizosaccharomyces species have been described (''S. pombe'', ''S. japonicus'', ''S. octosporus'', ''S. cryophilus'' and ''S. ...

, Debaryomyces,

Brettanomyces ''Brettanomyces'' is a non-spore forming genus of yeast in the family Saccharomycetaceae, and is often colloquially referred to as "Brett". The genus name ''Dekkera'' is used interchangeably with ''Brettanomyces'', as it describes the teleomorph ...

, Torulopsis, Nematospora,'' and ''Nadsonia'' genera. Increasing concentrations of glucose accelerates

glycolysis Glycolysis is the metabolic pathway that converts glucose () into pyruvate (). The free energy released in this process is used to form the high-energy molecules adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide (NADH ...

(the breakdown of glucose) which results in the production of appreciable amounts of ATP through substrate-level

phosphorylation In chemistry, phosphorylation is the attachment of a phosphate group to a molecule or an ion. This process and its inverse, dephosphorylation, are common in biology and could be driven by natural selection. Text was copied from this source, wh ...

. This reduces the need of

oxidative phosphorylation Oxidative phosphorylation (UK , US ) or electron transport-linked phosphorylation or terminal oxidation is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing chemical energy in order to produce adenosine tri ...

done by the TCA cycle via the

electron transport chain An electron transport chain (ETC) is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples th ...

and therefore decreases oxygen consumption. The phenomenon is believed to have evolved as a competition mechanism (due to the antiseptic nature of ethanol) around the time when the first fruits on Earth fell from the trees. The Crabtree effect works by repressing

respiration Respiration may refer to: Biology * Cellular respiration, the process in which nutrients are converted into useful energy in a cell ** Anaerobic respiration, cellular respiration without oxygen ** Maintenance respiration, the amount of cellul ...

by the

fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food ...

pathway, dependent on the substrate. Ethanol formation in Crabtree-positive yeasts under strictly aerobic conditions was firstly thought to be caused by the inability of these organisms to increase the rate of respiration above a certain value. This critical value, above which alcoholic fermentation occurs, is dependent on the strain and the culture conditions. More recent evidences demonstrated that the occurrence of alcoholic fermentation is not primarily due to a limited respiratory capacity, but could be caused by a limit in the cellular

Gibbs energy In thermodynamics, the Gibbs free energy (or Gibbs energy; symbol G) is a thermodynamic potential that can be used to calculate the maximum amount of work (physics), work that may be performed by a closed system, thermodynamically closed system a ...

dissipation rate. For ''S. cerevisiae'' in aerobic conditions, glucose concentrations below 150 mg/L did not result in ethanol production. Above this value, ethanol was formed with rates increasing up to a glucose concentration of 1000 mg/L. Thus, above 150 mg/L glucose the organism exhibited a Crabtree effect. It was the study of tumor cells that led to the discovery of the Crabtree effect. Tumor cells have a similar metabolism, the Warburg effect, in which they favor

over the

pathway.

References

Further reading