Analysis and Manipulation of Aspartate Pathway Genes for l-Lysine Overproduction from Methanol by Bacillus methanolicus

ABSTRACTWe investigated the regulation and roles of six aspartate pathway genes inl-lysine overproduction inBacillus methanolicus:dapG, encoding aspartokinase I (AKI);lysC, encoding AKII;yclM, encoding AKIII;asd, encoding aspartate semialdehyde dehydrogenase;dapA, encoding dihydrodipicolinate synthase; andlysA, encodingmeso-diaminopimelate decarboxylase. Analysis of the wild-type strain revealed thatin vivo lysCtranscription was repressed 5-fold byl-lysine and induced 2-fold bydl-methionine added to the growth medium. Surprisingly,yclMtranscription was repressed 5-fold bydl-methionine, while thedapG,asd,dapA, andlysAgenes were not significantly repressed by any of the aspartate pathway amino acids. We show that thel-lysine-overproducing classicalB. methanolicusmutant NOA2#13A52-8A66 has—in addition to ahom-1mutation—chromosomal mutations in thedapGcoding region and in thelysApromoter region. No mutations were found in itsdapA,lysC,asd, andyclMgenes. The mutantdapGgene product had abolished feedback inhibition bymeso-diaminopimelatein vitro, and thelysAmutation was accompanied by an elevated (6-fold)lysAtranscription levelin vivo. Moreover,yclMtranscription was increased 16-fold in mutant strain NOA2#13A52-8A66 compared to the wild-type strain. Overexpression of wild-type and mutant aspartate pathway genes demonstrated that all six genes are important forl-lysine overproduction as tested in shake flasks, and the effects were dependent on the genetic background tested. Coupled overexpression of up to three genes resulted in additive (above 80-fold) increasedl-lysine production levels.