Zymomonas mobilis

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.

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Z. mobilis degrades sugars to pyruvate using the Entner-Doudoroff pathway. The pyruvate is then fermentated 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:

• 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, fructose, and sucrose. Using biotechnological methods, scientists are currently trying to overcome this. A variant of Z. mobilis that is able to use certain pentoses 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 sterols. This allows it to have an extraordinary tolerance to ethanol in its environment, around 13%.