Use of Auxotrophic Mutants to Isolate LL- or DD-Isomers of 2,6-Diaminopimelic Acid

Abstract

S U M M A R YPseudomonas 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 pyruvate and additional (NH,),SO,. The excreted LL-isomer was isolated from the culture filtrate by ionexchange chromatography and purified by crystallization ( I -7 g/9 1 culture).A diaminopimelate-requiring mutant of Bacillus megaterium NCIB758 I grew on LL-and/or meso-diaminopimelate but not on the DD-isomer. This mutant was used to isolate the DD-isomer from a mixture of synthetic LL-and DD-diaminopimelate. It was grown in a minimal medium containing glycerol as carbon source and LLplus DD-diaminopimelate at a growth-limiting concentration (300 mg 1-l) ; when growth stopped, the DD-diaminopimelate that remained in the culture was isolated and crystallized (I -0 g/I I I culture). I N T R O D U C T I O N2,6-Diaminopimelic acid (Dap) exists in three stereoisomeric forms : the LL-, DD-and meso-isomers (Work, 1963). Authentic samples of each are required in studies of the isomeric composition of Dap in walls and spores of bacteria.Diaminopimelate synthesized chemically is a mixture of all three isomers : about 50 % meso-, 25 % LL-and 25 % DD-isomer (see later). Diaminopimelate can also be isolated from the culture filtrates of lysine-requiring mutants of Escherichia coli (Work, 1963) ; such Dap is a mixture of about 75 % meso-and 25 % LL-isomers (White & Kelly, 1965). The mesoDap can be separated from the other two isomers by crystallization because it is less soluble in ethanol/water. From the meso-plus LL-Dap mixture obtained by excretion (i.e. 'fermentation Dap '), pure LL-Dap can be recovered after precipitation of meso-Dap. Until recently, commercial Dap was 'fermentation material ' ; but at present, only synthetic Dap can be bought. Removing the meso-isomer from synthetic Dap leaves a mixture of the LL-and DD-isomers, which are difficult to separate. Work et al. (1955) separated the three isomers by preparing their diamides, treating these with a stereospecific amidase (which deaminated groups in the L-configuration only), and then separating the mixture of free LL-Dap, DD-Dap diamide and meso-Dap (D-)monoamide on an ion-exchange column.Free DD-and meso-Dap were regenerated by acid hydrolysis of the amides. A later modification of this method was described by Wade et al. (1957). These methods are relatively laborious and result in low yields of the pure isomers.In this paper, we describe the isolation of LL-Dap from cultures of a mutant of Pseudomonas aeruginosa (called PAC7) which excretes solely the LL-isomer (Clarkson & Meadow,

Metabolism of DD-2,6-Diaminopimelic Acid by a Diaminopimelate-requiring Mutant of Bacillus megaterium

“…LL-and DD-) A,pm. Saleh & White (1976) found that culture filtrates of this mutant, after growth had stopped on limiting amounts of racemic A,pm, always contained less residual DD-A,pm than had originally been added to the medium in the racemate.…”

“…The A,pm-requiring mutant (SWl) of B. megaterium isolated by Saleh & White (1976) lacks the enzyme N-acetyl-LL-diaminopimelate deacylase. This enzyme was detected in the wild-type (grown without A,pm) with an activity just enough to produce L L -A ,~~ (assuming 60pg is needed for growth of 1 mg of new organisms, see Results) at a rate sufficient to allow the observed doubling time of 90 min in medium A1 at 37 "C. Growth of the wild-type with A,pm did not repress the enzyme, and so it is very unlikely that the enzyme was absent from mutant SWl as a consequence of the presence of A,pm in the medium.…”

“…,~~. From its optical rotation and other properties (Saleh & White, 1976), the D D -A ,~~ must have been at least 95 yo (w/w) pure. No LL-isomer could be detected in the D D -A ,~~ by paper chromatography, and growth of mutant SW1 with D D -A ,~~ (400 pg ml-l) was very sparse, whereas mutant SW2 grew to 0.5 mg dry wt ml-l when the same D D -A ,~~ was supplied at 100 pg ml-l.…”

Regulation of the Enzymes of Lysine Biosynthesis in Bacillus sphaericus NCTC 9602 during Vegetative Growth

“…The preparations of aspartic /?-semialdehyde, dihydrodipicolinate and L-2-amino-6-ketopimelate (tetrahydrodipicolinate) have been described before (White, 1983). meso-Diaminopimelic acid was isolated by fractional crystallization from synthetic material (Work, 1963); LL-and DD isomers were obtained as described by Saleh & White (1976).…”

The Regulation of Diaminopimelate Decarboxylase Activity in Escherichia coli strain W

“…Pfizer & Co., Groton, Connecticut, U.S.A. From it, meso-and LL-diaminopimelate were isolated as described by White, Lejeune & Work (I 969). Do-Diaminopimelate was isolated from synthetic diaminopimelic acid as described by Saleh & White (1975). [ ~-l~C]Diaminopimelate was purchased from Calatomic, 54984 Terminal Annex, Los Angeles, California, U.S. A.…”