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We here present the pyc gene encoding pyruvate carboxylase (PC), and the hom-1 and hom-2 genes encoding two active homoserine dehydrogenase (HD) proteins, in methylotrophic Bacillus methanolicus MGA3. In general, both PC and HD are regarded as key targets for improving bacterial L-lysine production; PC plays a role in precursor oxaloacetate (OAA) supply while HD controls an important branch point in the L-lysine biosynthetic pathway. The hom-1 and hom-2 genes were strongly repressed by L-threonine and L-methionine, respectively. Wild-type MGA3 cells secreted 0.4 g/l L-lysine and 59 g/l L-glutamate under optimised fed batch methanol fermentation. The hom-1 mutant M168-20 constructed herein secreted 11 g/l L-lysine and 69 g/l of L-glutamate, while a sixfold higher L-lysine overproduction (65 g/l) of the previously constructed classical B. methanolicus mutant NOA2#13A52-8A66 was accompanied with reduced L-glutamate production (28 g/l) and threefold elevated pyc transcription level. Overproduction of PC and its mutant enzyme P455S in M168-20 had no positive effect on the volumetric L-lysine yield and the L-lysine yield on methanol, and caused significantly reduced volumetric L-glutamate yield and L: -glutamate yield on methanol. Our results demonstrated that hom-1 represents one key target for achieving L-lysine overproduction, PC activity plays an important role in controlling L-glutamate production from methanol, and that OAA precursor supply is not a major bottleneck for L-lysine overproduction by B. methanolicus.

Amino acids are among the major products in biotechnology in both volume and value, and the global market is growing. Microbial fermentation is the dominant method used for industrial production, and today the most important microorganisms used are Corynebacteria utilizing sugars. For low-prize bulk amino acids, the possibility of using alternative substrates such as methanol has gained considerable interest. In this mini review, we highlight the unique genetics and favorable physiological traits of thermotolerant methylotroph Bacillus methanolicus, which makes it an interesting candidate for overproduction of amino acids from methanol. B. methanolicus genes involved in methanol consumption are plasmid-encoded and this bacterium has a high methanol conversion rate. Wild-type strains can secrete 58 g/l of L: -glutamate in fed-batch cultures at 50 degrees C and classical mutants secreting 37 g/l of L: -lysine have been selected. The relative high growth temperature is an advantage with respect to both reactor cooling requirements and low contamination risks. Key genes in L: -lysine and L: -glutamate production have been cloned, high-cell density methanol fermentation technology established, and recently a gene delivery method was developed for this organism. We discuss how this new knowledge and technology may lead to the construction of improved L: -lysine and L: -glutamate producing strains by metabolic engineering.