Corynebacterium glutamicum
Jacob Roam

Corynebacterium glutamicum is a very important fermentative bacteria most widely know for its role in the production of monosodium glutamate, or MSG. Discovered in 1957 in Japan as a natural producer of glutamic acid, C. glutamicum is a Gram positive, facultatively anaerobic, heterotrophic bacterium with an irregular rod shape in a V-formation. It is non-pathogenic and is found in soil, animal feces, fruits and vegetables. Though it was originally isolated for its ability to produce massive amounts of glutamic acid, C. glutamicum and closely related organisms have been developed for the production of most of the biogene amino acids, nucleotides, and vitamins. Because of this ability it has undergone extensive genetic study to understand its production pathways.

The isolation of C. glutamicum as a producer of glatamic acid and sequentially for the large-scale production of MSG was achieved in post WWII Japan by Japanese researchers led by S. Kinoshita at Kyowa Hakko Kogyo Co. They found soil bacteria that produced large amounts of glutamic acid. They made two duplicate plates and after letting them grow for awhile, they killed the bacterium on one plate by UV irradiation. They then inoculated that plate with Leuconostoc mesenteroides, a bacteria that will only grow in the presence of glutamic acid. By looking at the locations of the L. mesenteroides colonies and comparing to the duplicate plate, they isolated the glutamic acid producing bacteria, C. glutamicum. Wild-type strains of this bacterium were found to produce about 10 g/L glutamic acid, and with genetic engineering yields are now upwards of 100g/L.
The thing that distinguishes C. glutamicum from similar bacteria that produce the glutamic acid is the amount that is produced. Glutamic acid is made by extracting alpha-ketogluterate from the TCA cycle by way a reductive amination by NADP+ specific glutamate dehydrogenase. The reason that C. glutamicum produces so much more than similar bacteria is not known for sure. A widely accepted theory used to be that C. glutamicum had very little alpha-ketogluterate dehydrogenase, the enzyme needed to continue the TCA cycle, so it was forced to produce glutamic acid. That was not necessarily disproved because of the difficulty of isolating alpha-ketogluterate dehydragenase, but it is now thought to have more to do with concentrations of glutamic acid inside the cell.

MSG, a flavor inhancer, has been widely used in the food industry for many years now. It is made by growing C. glutamicum in a medium containing sugars, molasses or starch as a fermentation substrate. The glutamic acid that they produce is merely filtered out of the medium and neutralized to make monosodium glutamate. After additional purification, crystallization, and drying, a white powder of monosodium glutamate is ready to use as flavor enhancer. MSG is a most common product made using C. glutamicum, but it is used for the production of many other amino acids and vitamins.

References

The Prokaryotes : a handbook on the biology of bacteria : ecophysiology, isolation, identification, applications / edited by Albert Balows ... [et al.]. New York : Springer-Verlag, c1992. 2nd ed.

Prof. Dr. Alfred Pühler, “Fermentative Production of Amino Acids and Vitamins by Corynebacteria.”
<http://www.genetik.uni-bielefeld.de/Genetik/coryne/coryne.eng.html>

Wageningen University, “Monosodiumglutamate - E621 -.” <http://www.food-info.net/uk/intol/msg.htm>

“Amino Acid Production.” <http://www.holisticmed.net/aspartame/aminoacid.pdf>

*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.

 

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