l-Lysine biosynthetic pathway of Methylophilus methylotrophus and construction of an l-lysine producer

Previously, we showed that the enzymes aspartokinase (AK) and dihydrodipicolinate synthase (DDPS), which are involved in l-lysine biosynthesis in the Gram-negative obligate methylotroph Methylophilus methylotrophus AS1, were inhibited by allosteric effectors, including l-lysine. To elucidate further the regulation of l-lysine biosynthesis in M. methylotrophus, we cloned the genes encoding three other enzymes involved in this pathway, l-aspartate-β-semialdehyde dehydrogenase, dihydrodipicolinate reductase (DDPR) and diaminopimelate decarboxylase, and examined their properties. DDPR was markedly inhibited by l-lysine. Based on this and our previous results, we constructed an l-lysine-producing strain of M. methylotrophus by introducing well-characterized genes encoding desensitized forms of AK and DDPS, as well as dapB (encoding DDPR) from Escherichia coli, using a broad host range plasmid. l-Lysine production was significantly increased by employing an S-(2-aminoethyl)-l-cysteine (l-lysine analog)-resistant mutant as the host. This derivative accumulated l-lysine at a concentration of 1 g l−1 of medium using methanol as a carbon source.