Germination of Bacterial Spores by Calcium Chelates of Dipicolinic Acid Analogues

Calcium salts of analogues of dipicolinic acid were substituted for calcium dipicolinate in tests of germination of spores of Bacillus megaterium ATCC 10778. Only 4H-pyran-2,6-dicarboxylic acid was as active as dipicolinic acid. 3-Methyldipicolinic acid and 4-methyl-4H-pyran-2,6-dicarboxylic acid were active but the germination proceeded less rapidly. In the presence of a threshold concentration (0.020 m) of calcium dipicolinate, calcium salts of pyrimidine-2,4-dicarboxylate, pyrazine-2,6-dicarboxylate, 4-hydroxydipicolinate, and furan-2,5-dicarboxylate also showed activity. A hypothesis is proposed for mobilization of native calcium dipicolinate of dormant spores during germination, by way of a dimerization like that exhibited in crystals of calcium dipicolinate trihydrate and the isostructural calcium pyrandicarboxylate trihydrate. The compounds 4-bis(2-hydroxyethyl)iminopyridine-2,6-dicarboxylic acid and ethyl ester, 3-methyl-2,6-distyryl-pyridine, 3-methylpyridine-2,6-dicarboxylic acid, and pyrimidine-2,4-dicarboxylic acid are reported for the first time. Calcium and proton association constants are given for various ligands.