Zymomonas mobilis
A Microbial Biorealm page on the genus Zymomonas mobilis
Classification
Higher order taxa
Bacteria; Proteobacteria; Alpha Proteobacteria; Sphingomonadales; Sphingomonadaceae[Others may be used.
Species
Zymomonas mobilis
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NCBI: Taxonomy |
Description and significance
Zymomonas mobilis is a rod shaped gram negative bacterium that can be found in sugar rich plant saps. It is usually 2-6μm long and 1-1.4 μm wide, but this can vary significantly. In high CO2 or ethanol concentrations slime and granular layers have been see around the cell. It has been isolated from sugar cane as well as alcoholic beverages such as African palm wine; it is also known to cause cider sickness and spoiling of beer. However, the spoiling of beer is very limited due to its optimal temperature range of 25-30°C. It is being studied for its ability to ferment sugar to ethanol. Its ability to efficiently ferment carbohydrates using the Enter-Doudoroff pathway makes it an attractive candidate for producing bioethanol for fuel. It has also shown a high growth rate, tolerance to ethanol as well as being amendable to engineering [1] [2].
Genome structure
There is currently one compete genome sequence and one in progress for the NCBI genome list for zymomonas mobilis. The genome has a circular chromosomes with 1,998 open reading frames, three ribosomal RNA transcription units and is made up of 2,056,416 base pairs. It has an overall G+C content of 46.3%. It appears to only be able to metabolize glucose through the Entner-Doudoroff pathway because the genome does not have recognized genes for 6-phosphofructokinase, an enzyme essential for the Embden-Meyerhof-Parnas pathway as well as lacking the genes for the enzymes 2-oxoglutarate dehydrogenase complex and malate dehydrogenase both of which are involved in the tricarboxylic acid cycle [4].
Cell structure and metabolism
Zymomonas mobilis is a gram negative bacteria. It is rod-shaped and not mobile. Z. mobilis has hopanoids in its plasma membrane, this is thought to be a key to its high tolerance to ethanol. Its plasma membrane has a phospholipids composition with a major component of phosphatidylethanolamine and lesser amounts of phosphatidylglycerol, cardiolipin, dimethyl phosptidylethanolamine and phosphatidylcholine. In environments with increased ethanol and glucose cause a decrease in phosphatidylethanolamine and phosphatidylglycerol and an increase in phosphatidylcholine [1]. It uses the Enter-Doudoroff pathway for fermentation, making it very efficient and able to produce ethanol near theoretical levels. It is unable to utilize other pathways to obtain energy as it appears to lack key enzymes for the Embden-Meyerhof-Parnas pathway and the tricarboxylic acid cycle. In its naturally occurring form it can only metabolize glucose, fructose and sucrose to ethanol, it is unable to ferment more complex carbohydrates. However, with engineering strains have been produced that are capable of metabolizing complex carbohydrates, this is an area that is being heavily researched [3]. Also, sucrose can cause problems for the efficiency of fermentation because of byproducts which are produced such as levan and sorbitol, this greatly increases the biomass limiting ethanol production [2]. Ethanol production inhibition may also be caused by the presence of acetic, formic or propionic acids as well as higher concentrations of oxygen and carbon dioxide. However, ethanol itself seems to be the biggest inhibitor because of its affect on the plasma membrane, it cause the membrane to become more permeable allowing some cofactors and coenzymes from the Entner-Douduroff pathway to leave [1].
Ecology
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Pathology
How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.
Application to Biotechnology
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Current Research
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References
Edited by David Ly student of Rachel Larsen and Kit Pogliano
