CONSTRUCTION OF L-LYSINE-OVERPRODUCING STRAINS OF BREVIBACTERIUM-LACTOFERMENTUM BY TARGETED DISRUPTION OF THE HOM AND THRB GENES

The mobilization of plasmids from gram-negative Escherichia coli to gr am-positive Brevibacterium lactofermentum, mediated by P-type transfer functions, was used to construct disrupted mutants blocked specifical ly in the homoserine branch of the aspartate pathway. The mutant strai n B. lactofermentum R31 showed an efficiency of conjugal transfer two to three orders of magnitude higher than that of the wild-type strain B. lactofermentum ATCC 13869. The hom- and thrB-disrupted mutants of B . lactofermentum ATCC 13869 were lysine overproducers. B. lactoferment um R31 mutants do not overproduce lysine because R31 is an alanine-ove rproducing strain and channels the pyruvate needed for lysine biosynth esis to the production of alanine.