BIOSYNTHESIS OF DIPICOLINIC ACID IN BACILLUS MEGATERIUM

Very little is known of the precursors of the dipicolinic acid (pyridine-2,6-dicarboxylic acid) in bacterial spores. C'4-2,6-diaminopimelic acid was shown to contribute to the formation of dipicolinic acid in Bacillus cereus var. mycoides (Perry and Foster, 1955; Foster, 1956) but the efficiency of the conversion was low, possibly because of a slow penetration of the cells by the exogenously supplied, labeled compound. Also, the data did not differentiate between a ring closure of the intact carbon chain and a breakdown to smaller precursors of dipicolinic acid. In other organisms, the related a-picolinic acid (pyridine-2-carboxylic acid) and nicotinic acid (pyridine-3-carboxylic acid) are produced from 3-hydroxyanthranilic acid by steps that are still unclarified (Mehler, 1956; Meister, 1957; Yanofsky, 1955). A nonenzymatic reaction of an intermediate may occur to form quinolinic acid (pyridine-2,3-dicarboxylic acid) (Mehler, 1956). Presently available information on the biosynthesis of pyridine rings does not permit a decision as to whether an identical mechanism is operative in the formation of the above pyridine derivatives. The present study was designed to reveal the extent to which several common metabolites contribute carbon to the biosynthesis of dipicolinic acid in sporulating bacteria. Two types of experiments were used. In one, selected C14_ labeled compounds were furnished exogenously to sporulating cells; the degree of incorporation of radioactivity into dipicolinic acid was taken as an indication of the extent to which the respective compounds participated in the biosynthesis of dipicolinic acid. In the second, the isotope competition technique was employed (Roberts et al., 1955). Here, various unlabeled metabolites were furnished exogenously to C14-labeled sporu-