Aerobic fermentation
While aerobic fermentation does not produce adenosine triphosphate (ATP) in high yield, it allows proliferating cells to convert nutrients such as glucose and glutamine more efficiently into biomass by avoiding unnecessary catabolic oxidation of such nutrients into carbon dioxide, preserving carbon-carbon bonds and promoting anabolism.
[1] The Crabtree effect is a regulatory system whereby respiration is repressed by fermentation, except in low sugar conditions.
Many Crabtree-positive yeast species are used for their fermentation ability in industrial processes in the production of wine, beer, sake, bread, and bioethanol.
[4] It was believed that the WGD was a mechanism for the development of the Crabtree effect in these species due to the duplication of alcohol dehydrogenase (ADH) encoding genes and hexose transporters.
[9] Later evolutionary events that aided in the evolution of aerobic fermentation are better understood and outlined in the section discussing the genomic basis of the Crabtree effect.
[2] These fruits provided an abundance of simple sugar food source for microbial communities, including both yeast and bacteria.
[4] This is supported by research that determined the kinetic behavior of the ancestral ADH protein, which was found to be optimized to make ethanol, rather than consume it.
[4] In high sugar environments, S. cerevisiae outcompetes and dominants all other yeast species, except its closest relative Saccharomyces paradoxus.
[18] The genomic basis of the Crabtree effect is still being investigated, and its evolution likely involved multiple successive molecular steps that increased the efficiency of the lifestyle.
pombe is a Crabtree-positive yeast, which developed aerobic fermentation independently from Saccharomyces lineage, and detects glucose via the cAMP-signaling pathway.
[20] The number of transporter genes vary significantly between yeast species and has continually increased during the evolution of the S. cerevisiae lineage.
[12] A little over half of WGD gene pairs in the glycolysis reaction pathway were retained in post-WGD species, significantly higher than the overall retention rate.
[12] The WGD is believed to have played a beneficial role in the evolution of the Crabtree effect in post-WGD species partially due to this increase in copy number of glycolysis genes.
[13] The ancestral, or original, Adh had a similar function as Adh1 and after a duplication in this gene, Adh2 evolved a lower KM for ethanol.
Mitochondrial ribosomal proteins expression is only induced under environmental stress conditions, specifically low glucose availability.
Beer and other alcoholic beverages, throughout human history, have played a significant role in society through drinking rituals, providing nutrition, medicine, and uncontaminated water.
This often favors specialization adaptations in domesticated microbes, associated with relaxed selection for non-useful genes in alternative metabolic strategies or pathogenicity.
[16] For example, the important industrial yeast strain Saccharomyces pastorianus is an interspecies hybrid of S. cerevisiae and the cold tolerant S.
[23] Cancers cells often have reprogrammed their glucose metabolism to perform lactic acid fermentation, in the presence of oxygen, rather than send the pyruvate made through glycolysis to the mitochondria.
[8] Alcoholic fermentation is often used by plants in anaerobic conditions to produce ATP and regenerate NAD+ to allow for glycolysis to continue.
Tobacco pollen, similar to Crabtree-positive yeast, perform high levels of fermentation dependent on the sugar supply, and not oxygen availability.
Cytoplasmic male sterility is a trait observed in maize, tobacco and other plants in which there is an inability to produce viable pollen.
It is believed that this trait might be due to the expression of the fermentation genes, ADH and PDC, a lot earlier on in pollen development than normal and the accumulation of toxic aldehyde.
