Use of auxotrophic mutants to isolate LL- or DD-isomers of 2,6-diaminopimelic acid.

Pseudomonas aeruginosa PAC7 (a mutant deficient in diaminopimelate epimerase), excreted diaminopimelate (solely LL-isomer) after growth in a minimal medium plus lysine with succinate as carbon source. More diaminopimelate was excreted when bacteria were transferred at the end of the exponential phase of growth into fresh minimal medium without lysine but supplemented with pyrivate and additional (NH4)2SO4. The excreted LL-isomer was isolated from the culture filtrate by ion-exchange chromatography and purified by crystallization (1.7 g/9 1 culture). A diaminopimelate-requiring mutant of Bacillus megaterium NCIB7581 grew on LL- and/or meso-diaminopimelate but not on the DD-isomer. This mutant was used to isolate the DD-idomer from a mixture of synthetic LL- and DD-diaminopimelate. It was grown in a minimal medium containing glycerol as carbon source and LL- plus DD-diaminopimelate at a growth-limiting concentration (300 mg l-1); when growth stopped, the DD-diaminopimelate that remained in the culture was isolated and crystallized (1.0 g/II l culture).