Zymomonas mobilis
Encyclopedia
Zymomonas mobilis is a bacterium belonging to the genus Zymomonas
. It is notable for its bioethanol-producing capabilities, which surpass yeast
in some aspects. It was originally isolated from alcoholic beverages like the African palm wine, the Mexican pulque
, and also as a contaminant of cider and beer in European countries.
Z. mobilis degrades sugars to pyruvate using the Entner-Doudoroff pathway
. The pyruvate is then fermented
to produce ethanol
and carbon dioxide
as the only products (analogous to yeast).
The advantages of Z. mobilis over S. cerevisiae with respect to producing bioethanol:
However, it has a severe limitation compared to yeast: its utilizable substrate range is restricted to glucose
, fructose
, and sucrose
. Using biotechnological
methods, scientists are currently trying to overcome this. A variant of Z. mobilis that is able to use certain pentose
s as a carbon source has been developed.
An interesting characteristic of Z. mobilis is that its plasma membrane contains hopanoids
, pentacyclic compounds similar to eukaryotic sterol
s. This allows it to have an extraordinary tolerance to ethanol in its environment, around 13%.
Zymomonas
Zymomonas is a genus of bacteria. The best known species from this genus is Zymomonas mobilis. Members of this genus are gram negative, facultative anaerobic, non-sporulating, polarly-flagellated, rod-shaped bacteria....
. It is notable for its bioethanol-producing capabilities, which surpass yeast
Yeast
Yeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...
in some aspects. It was originally isolated from alcoholic beverages like the African palm wine, the Mexican pulque
Pulque
Pulque, or octli, is a milk-colored, somewhat viscous 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...
, and also as a contaminant of cider and beer in European countries.
Z. mobilis degrades sugars to pyruvate using the Entner-Doudoroff pathway
Entner-Doudoroff Pathway
The 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 fermented
Fermentation (biochemistry)
Fermentation is the process of extracting energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound. In contrast, respiration is where electrons are donated to an exogenous electron acceptor, such as oxygen,...
to produce ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
and carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
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 glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
, fructose
Fructose
Fructose, or fruit sugar, is a simple monosaccharide found in many plants. It is one of the three dietary monosaccharides, along with glucose and galactose, that are absorbed directly into the bloodstream during digestion. Fructose was discovered by French chemist Augustin-Pierre Dubrunfaut in 1847...
, and sucrose
Sucrose
Sucrose is the organic compound commonly known as table sugar and sometimes called saccharose. A white, odorless, crystalline powder with a sweet taste, it is best known for its role in human nutrition. The molecule is a disaccharide composed of glucose and fructose with the molecular formula...
. Using biotechnological
Biotechnology
Biotechnology is a field of applied biology that involves the use of living organisms and bioprocesses in engineering, technology, medicine and other fields requiring bioproducts. Biotechnology also utilizes these products for manufacturing purpose...
methods, scientists are currently trying to overcome this. A variant of Z. mobilis that is able to use certain pentose
Pentose
A pentose is a monosaccharide with five carbon atoms. Pentoses are organized into two groups. Aldopentoses have an aldehyde functional group at position 1...
s as a carbon source has been developed.
An interesting characteristic of Z. mobilis is that its plasma membrane contains hopanoids
Hopanoids
Hopanoids are natural pentacyclic compounds based on the chemical structure of hopane. Their primary function is to improve plasma membrane strength and rigidity in bacteria. In eukaryotes cholesterol serves a similar function...
, pentacyclic compounds similar to eukaryotic sterol
Sterol
Sterols, also known as steroid alcohols, are a subgroup of the steroids and 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%.