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Microbiology 152 (2006), 105-112; DOI  10.1099/mic.0.28092-0
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Microbiology 152 (2006), 105-112; DOI  10.1099/mic.0.28092-0
© 2006 Society for General Microbiology

Regulation of aspartokinase, aspartate semialdehyde dehydrogenase, dihydrodipicolinate synthase and dihydrodipicolinate reductase in Lactobacillus plantarum

Muhammad N. Cahyanto{dagger}, Hiroko Kawasaki, Mariko Nagashio, Kazuhito Fujiyama and Tatsuji Seki

The International Center for Biotechnology, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan

Correspondence
Hiroko Kawasaki
ICBKawasakiNakagawa{at}icb.osaka-u.ac.jp

The use of a lysine-overproducing strain of Lactobacillus plantarum in food or feed fermentations may lead to the production of lysine-rich products. The availability of functional genes and information on the regulation of lysine biosynthesis are required to develop a lysine-overproducing strain. The genome sequence of L. plantarum revealed putative lysine biosynthetic genes, some of which may produce isozymes. This study examined the functionality of the genes and the regulation of the first four enzymes of lysine biosynthesis, together with homoserine dehydrogenase, in L. plantarum. The genes were expressed in Escherichia coli, and the regulation of the enzymes was studied in cell extracts of both recombinant E. coli and L. plantarum. Among seven lysine biosynthetic genes studied (aspartokinase genes, thrA1 and thrA2; aspartate semialdehyde dehydrogenase genes, asd1 and asd2; dihydrodipicolinate synthase genes, dapA1 and dapA2; and the dihydrodipicolinate reductase gene, dapB) plus two homoserine dehydrogenase genes (hom1 and hom2), the products of six genes, i.e. thrA2, asd2, dapA1, dapB, hom1 and hom2, showed obvious enzyme activities in vitro. The product of one of the homoserine dehydrogenase genes, hom1, exhibited both homoserine dehydrogenase and aspartokinase activities. However, the aspartokinase activity was mainly due to ThrA2 and was inhibited by L-lysine and repressed by L-threonine, and the homoserine dehydrogenase activity was mainly due to Hom2 and was inhibited by L-threonine. The aspartate semialdehyde dehydrogenase, dihydrodipicolinate synthase and dihydrodipicolinate reductase were not regulated by the end-products of the pathway.

{dagger}Present address: Department of Food and Agricultural Product Technology, Gadjah Mada University, Bulaksumur, Yogyakarta 55281, Indonesia.






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Copyright © 2006 Society for General Microbiology.