Zymomonas mobilis is a bacterium belonging to the genus
ZymomonasZymomonas is a genus of bacteria. The best known species from this genus is Zymomonas mobilis. Members of this genus are gram negative, anaerobic, non-sporulating, polarly-flagellated, rod-shaped bacteria....
. It is notable for its bioethanol-producing capabilities, which surpass
yeastYeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with about 1,500 species currently described; they dominate fungal diversity in the oceans. Most reproduce asexually by budding, although a few do so by binary fission...
in some aspects. It was originally isolated from alcoholic beverages like the African palm wine, the Mexican
pulquePulque, or octli, is an alcoholic beverage made from the fermented sap of the maguey plant, and is a traditional native beverage of Mexico. The drink’s history extends far back into the Mesoamerican period, when it was considered sacred, and its use was limited to certain classes of people...
, and also as a contaminant of cider and beer in European countries.
Z. mobilis degrades sugars to pyruvate using the
Entner-Doudoroff pathwayThe Entner-Doudoroff pathway describes an alternate series of reactions that catabolize glucose to pyruvate using a set of enzymes different from those used in either glycolysis or the pentose phosphate pathway. Most bacteria use glycolysis and the pentose phosphate pathway...
.
Zymomonas mobilis is a bacterium belonging to the genus
ZymomonasZymomonas is a genus of bacteria. The best known species from this genus is Zymomonas mobilis. Members of this genus are gram negative, anaerobic, non-sporulating, polarly-flagellated, rod-shaped bacteria....
. It is notable for its bioethanol-producing capabilities, which surpass
yeastYeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with about 1,500 species currently described; they dominate fungal diversity in the oceans. Most reproduce asexually by budding, although a few do so by binary fission...
in some aspects. It was originally isolated from alcoholic beverages like the African palm wine, the Mexican
pulquePulque, or octli, is an alcoholic beverage made from the fermented sap of the maguey plant, and is a traditional native beverage of Mexico. The drink’s history extends far back into the Mesoamerican period, when it was considered sacred, and its use was limited to certain classes of people...
, and also as a contaminant of cider and beer in European countries.
Z. mobilis degrades sugars to pyruvate using the
Entner-Doudoroff pathwayThe Entner-Doudoroff pathway describes an alternate series of reactions that catabolize glucose to pyruvate using a set of enzymes different from those used in either glycolysis or the pentose phosphate pathway. Most bacteria use glycolysis and the pentose phosphate pathway...
. The pyruvate is then
fermentatedFermentation is the process of deriving energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound. This is in contrast to cellular respiration, where electrons are donated to an exogenous electron acceptor,...
to produce
ethanolEthanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug, best known as the type of alcohol found in alcoholic beverages and in modern thermometers. Ethanol is one of the oldest recreational drugs...
and
carbon dioxideCarbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
as the only products (analogous to yeast).
The advantages of
Z. mobilis over
S. cerevisiae with respect to producing bioethanol:
- higher sugar uptake and ethanol yield,
- lower biomass production,
- higher ethanol tolerance,
- does not require controlled addition of oxygen during the fermentation,
- amenability to genetic manipulations.
However, it has a severe limitation compared to yeast: its utilizable substrate range is restricted to
glucoseGlucose , a monosaccharide also known as - grape sugar, blood sugar, or corn sugar, is a very important carbohydrate in biology. The living cell uses it as a source of energy and metabolic intermediate...
,
fructoseFructose is a simple monosaccharide found in many foods. It is a white solid that dissolves readily in water. Honey, tree fruits, berries, melons, and some root vegetables, contain significant amounts of the fructose derivative sucrose...
, and
sucroseSucrose, commonly called table sugar, is a moosaccharide of glucose and fructose with the molecular formula C12H22O11. This white, odorless, crystalline powder has a pleasing, sweet taste. It is best known for its role in human nutrition...
. Using
biotechnologicalBiotechnology is technology based on biology, agriculture, food science, and medicine. Modern use of the term usually refers to genetic engineering as well as cell- and tissue culture technologies...
methods, scientists are currently trying to overcome this. A variant of
Z. mobilis that is able to use certain
pentoseA pentose is a monosaccharide with five carbon atoms.They either have an aldehyde functional group in position 1 , or a ketone functional group in position 2 ....
s as a carbon source has been developed.
An interesting characteristic of
Z. mobilis is that its plasma membrane contains
hopanoidsHopanoids are pentacyclic compounds , whose primary function is to improve plasma membrane fluidity in Bacteria. In eukaryotes cholesterol serves a similar function...
, pentacyclic compounds similar to eukaryotic
sterolSterols are an important class of organic molecules. They occur naturally in plants, animals and fungi, with the most familiar type of animal sterol being cholesterol...
s. This allows it to have an extraordinary tolerance to ethanol in its environment, around 13%.
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