Corynebacterium glutamicum

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A Microbial Biorealm page on the genus Corynebacterium glutamicum

Classification

Higher order taxa

Domain - Bacteria; Phylum - Actinobacteria; Class - Actinobacteria; Order - Actinomycetales; Family - Corynebacteriaceae

Species

Corynebacterium glutamicum

Description and significance

C. glutamicum is a small, non-moving Gram-positive soil bacterium. Physically, it is rod shaped with the ends swelled in a shape similar to a club. It does not produce spores. It contains catalase and uses fermentative metabolism to break down carbohydrates (1). It was first discovered in Japan in the 1950s, and it has particular importance in biotechnology (discussed below) (2). Another reason for researchers to sequence its genome is that it is a good model with which to understand other genera in the same monophylectic taxon (4).

Genome structure

C. glutamicum has a circular chromosome and a plasmid. Its genome consists of 3,314,179 nucleotides. This genome is taken from the wild-type strain C. glutamicum ATCC 13032. It also has one circular plasmid, pCGR1, which has 49,120 nucleotides. (3)

Cell structure and metabolism

C. glutamicum breaks down carbohydrates through the process of fermentation. It can take its carbon from many different sources, such as several aromatic compounds (5). Due to the variance in the availability of nutrients and carbon sources, C. glutamicum has 127 proteins associated with a regulatory function in transcription, which in turn control metabolism.

Of the structures C. glutamicum possesses, its cell wall is probably one of the most unique parts. Besides the peptidoglycan layer, the cell wall consists of short-chain mycolic acids, along with a couple of other unusual lipids (meso-diaminopimelic acids and arabino-galactan polymers) (1).

Through its metabolism, C. glutamicum synthesizes such products as serine, glutamate, and lysine (amino acids), all of which are used in many different ways, such as in pharmacies.

Ecology

C. glutamicum makes many contributions to the environment since it can be used in bioremediation, such as of arsenic (4). Research is also being done to use C. glutamicum to produce a biodegradable plastic (see below, under Current Research).

Pathology

C. glutamicum is a non-pathogenic bacterium, although a related species, C. diphtheriae is pathogenic and causes diphtheria in humans through a strong exotoxin it produces. It is usually treatable by antitoxins, toxoids, and antibiotics.

Application to Biotechnology

Several characteristics of C. glutamicum makes it useful in biotechnology. It is not pathogenic, does not form spores, grows quickly, has relatively few growth requirements, has no extracellular protease secretion, and has a relatively stable genome (4).

C. glutamicum produces several useful compounds and enzymes. It was first discovered as a producer of glutamate. Now it is also used to make amino acids, such as lysine, threonine, and isoleucine, as well as vitamins like pantothenate(2).

Another possible use for C. glutamicum is in bioremediation, such as for arsenic. C. glutamicum contains two operons in its genome, the ars1 and ars2 operons, that are resistant to arsenic. With further experimentation, researchers hope to be able to eventually use this bacterium to take up the arsenic in the environment(4).

Current Research

Because of the useful characterisitics of Corynebacterium, much research has been done on it to try to modify it in some way in order to make it more useful for humans.

One such way is by creating a biosynthetic pathway to produce poly(3-hydroxybutyrate) (P(3HB)), a polyester that can be used to make a biodegradable plastic. Plasmids were inserted into c. glutamicum, including an expression plasmid, that under certain conditions would create the P(3HB). This experiment was also done with E. coli. The results showed that although the P(3HB)s created differed slightly in properties and although E. coli had a higher P(3HB) content, C. glutamicum had almost four times higher cell density, making it a more efficient producer of the polyester. Further research will fine-tune the process as well as try to change the properties of the synthesized polyester even more. (5).

Another area of research into C. glutamicum is how to increase its production of L-glutamic acid, which is produced annually at a rate of about 1.5 million tons. One way is to get rid of CO₂, which would increase the production of L-glutamic acid. To do so, phosphoketolase was used in order to bypass a pathway in which CO₂ would normally have been synthesized. The yield of L-glutamic acid was increased by 9% by weight and productivity increased by 10%, implying that the technique was a success. This technique could be further developed, as well as transferred to increase production of other C. glutamicum products , such as other amino acids. (6)

In a related area of research, another group tried to increase L-serine production in C. glutamicum. Since serine has pharmaceutical uses and about 300 tons are produced annually, there is a lot of interest in researching its production. One of the intracellular processes that inhibits L-serine production involves an enzyme called serine hydroxymethyltransferase (SHMT), whose activity can be controlled by 5,6,7,8-tetrahydrofolate (THF). By deleting the genes for THF synthesis, an external folate source was needed for the growth of C. glutamicum, but SHMT use was controlled. This led to a higher yield of L-serine.(7)

References

1. Rollins, David M. "Pathogenic Microbiology." 2000. http://www.life.umd.edu/classroom/bsci424/PathogenDescriptions/Corynebacterium.htm

2. Kalinowski, Jörn, Dr. "Fermentative Production of Amino Acids and Vitamins by Corynebacteria". Universität Bielefeld. Genetik. http://www.genetik.uni-bielefeld.de/Genetik/coryne/coryne.eng.html

3. Genomic Sequence of Corynebacterium glutamicum. NCBI Database, http://www.ncbi.nlm.nih.gov/sites/entrez?db=genome&cmd=Retrieve&dopt=Overview&list_uids=20857

4. Mateos, Luis M., Efren Ordonez, Michal Letek, and Jose A. Gil. "Corynebacterium glutamicum as a model bacterium for the bioremediation of arsenic". International Microbiology. 2006. p. 207-215.

5. Jo, Sung-Jin, Michihisa Maeda, Toshihiko Ooi and Seiichi Taguchi. “Production System for Biodegradable Polyester Polyhydroxybutyrate by Corynebacterium glutamicum”. Journal of Bioscience and Bioengineering, Vol. 102, 233-236 (2006).

6. Chinen, Akito, Yuri I. Kozlov, Yoshihiko Hara, Hiroshi Izui and Hisashi Yasueda: “Innovative Metabolic Pathway Design for Efficient L-Glutamate Production by Suppressing CO2 Emission”. Journal of Bioscience and Bioengineering, Vol. 103, 262-269 (2007) .

7. Stolz, Michael, Petra Peters-Wendisch, Helga Etterich, Tanja Gerharz, Robert Faurie, Hermann Sahm, Holger Fersterra, and Lothar Eggeling. "Reduced Folate Supply as a Key to Enhanced L-Serine Production by Corynebacterium glutamicum." Applied and Environmental Microbiology, February 2007, p. 750-755, Vol. 73, No. 3

Edited by Giang Nguyen, student of Rachel Larsen and Kit Pogliano