Regulation of lysine and dipicolinic acid biosynthesis in Bacillus brevis ATCC 10068: significance of derepression of the enzymes during the change from vegetative growth to sporulation.

Lysine biosynthetic pathway enzymes of Bacillus brevis ATCC 1068 were studied as a function of stage of development (growth and sporulation). The synthesis of aspartic-2-semialdehyde dehydrogenase (ASA-dehydrogenase), dihydrodipicolinate synthase (DHDPA-synthase), DHDPA-reductase and diaminopimelate decarboxylase (DAP-decarboxylase) was found not to be co-regulated, since lysine was not a co-repressor for these enzymes. Unlike the aspartokinase isoenzymes, the other enzymes of the lysine pathway were not derepressed in thiosine-resistant, lysine-excreting mutants. Thus, the aspartokinase isoenzymes were the key enzymes during growth and regulation of lysine biosynthesis through restriction of L-ASA synthesis via feedback control by lysine on the aspartokinases was therefore suggested. In contrast to other Bacillus species, the levels of the lysine biosynthetic pathway enzymes of strain ATCC 10068 were not derepressed during the change from vegetative growth to sporulation. Two control mechanisms, enabling the observed preferential channelling of carbon for the synthesis of spore-specific diaminopimelic acid (DAP) and dipicolinic acid (DPA) were a) loss of DAP-decarboxylase, b) inhibition of DHDPA-reductase by DPA. Increase in the level of the DAP pool during sporulation, as a consequence of the loss of DAP-decarboxylase, and its relevance to the non-enzymatic formation of DPA has been discussed.