Dihydrodipicolinate eh?
References:
The organism I chose, Brevibacterium lactofermentum, is closely related to the organism Archer Daniels Midland was manipulating for industrial lysine production this summer: Corynebacterium glutamicum. Interestingly, while these two microbes are classified differently, they function similarly in the lysine biosynthetic pathway, which can be seen at the left. Both are gram-positive microbes that have high lysine extracellular yield. As of 1997, as much as 350,000 tons of L-lysine was produced annually with Coryne making it big business. In order to increase the profit margin for sale of lysine, practical genetic engineering techniques are currently being analyzed to augment production within the most active strains of this microbe. Some, such as M. Patek et al, in 1997 studied the dapB-ORF2-dapA-ORF4 sequence of genes to reveal the importance of the flanking open reading frames, especially ORF4. At this time, they had a pretty good idea of how the aspartate pathway was functioning all the way through to lysine. However, in 1993, Pisabarro et al were studying the dapA, dapB, and ORF2 genes in Brevibacterium lactofermentum and had very little idea of how the genes were working together. The gap of four year may not seem a long time, but they served to open the floodgates for exploitation of Brevibacterium lactofermentum as well as Corynebacterium.
In 1998, Eggeling et al published an article, "Improved L-lysine yield with Corynebacterium glutamicum: use of dapA resulting in increased flux combined with growth limitation," to show the importance of modification of a certain gene in the lysine biosynthetic pathway. Specifically, dapA codes for the enzyme dihydrodipicolinate synthase, which converts aspartate semialdehyde to dihydrodipicolinate at the branch point of the aspartate metabolic pathway. From there, the pathway splits into two branches, one with a single enzyme converting Piperideine dicarboxylate to Diaminopimelate, Diaminopimelate dehydrogenase (ddh), and another with a series of four enzymes, dapD, dapC, dapE, and dapF, which accomplish the same product. Diaminopimelate then is either incorporated into cell wall structure or converted to lysine by the lysA gene product and excreted by the lysE gene product, depending on intracellular concentrations. By increasing the amount of dihydrodipicolinate synthase present in the cellular machinery at the beginning of the lysine biosynthetic branchpoint, the resulting participants are induced and therefore yield more lysine. Eggeling et al mention the following at the conclusion of the paper, "the present study shows that even a classically obtained, very good amino-acid-producing strain can be improved." This statement shows the potential for genetic engineering is now, and the more we learn about the players in lucrative synthetic pathways, the more research efforts will be applied and demanded for profit motive.
Chatterjee, M. "Lysine Production by Brevibacterium linens and Its Mutants: Activities and Regulation of Enzymes of the Lysine Biosynthetic Pathway." Folia Microbiology, Vol43, 1998: 141-146.
Eggeling, L., Oberle, S., and Sahm, H. "Improved L-lysine yield with Corynebacterium glutamicum: use of dapA resulting in increased flux combined with growth limitation." Applied Microbiological Biotechnology, 1998, Vol 49: 24-30.
Patek, M., et al. "Identification and transcriptional analysis of the dapB-ORF2-dapA-ORF4 operon of Corynebacterium glutamicum, encoding two enzymes involved in L-lysine synthesis." Biotechnology Letters, Vol. 19, No. 11, Nov. 1997: 1113-1117.
Pisabarro, Agustin, et al. "A Cluster of Three Genes (dapA, orf2, and dapB) of Brevibacterium lactofermentum Encodes Dihydrodipicolinate Synthase, Dihydrodipicolinate Reductase, and a third Polypeptide of Unknown Function." Journal of Bacteriology, May 1993: 2743-2749.
Schrumpf, Barbel, et al. "A Functionally Split Pathway for Lysine Synthesis in Corynebacterium glutamicum." Journal of Bacteriology, July 1991: 4510-4516.
*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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