Dipicolinic acid (pyridine-2,6-dicarboxylic acid or PDC and DPA) is a chemical compound which plays a role in the heat resistance of bacterial endospores. It is also used to prepare dipicolinato ligated lanthanide and transition metal complexes for ion chromatography.[1]
Dipicolinic acid composes 5% to 15% of the dry weight of Bacillus subtilis spores.[2] [3] It has been implicated as responsible for the heat resistance of the endospore,[4] although mutants resistant to heat but lacking dipicolinic acid have been isolated, suggesting other mechanisms contributing to heat resistance are at work.[5] Two genera of bacterial pathogens are known to produce endospores: the aerobic Bacillus and anaerobic Clostridium.[6]
Dipicolinic acid forms a complex with calcium ions within the endospore core. This complex binds free water molecules, causing dehydration of the spore. As a result, the heat resistance of macromolecules within the core increases. The calcium-dipicolinic acid complex also functions to protect DNA from heat denaturation by inserting itself between the nucleobases, thereby increasing the stability of DNA.[7]
The high concentration of DPA in and specificity to bacterial endospores has long made it a prime target in analytical methods for the detection and measurement of bacterial endospores. A particularly important development in this area was the demonstration by Rosen et al. of an assay for DPA based on photoluminescence in the presence of terbium,[8] although this phenomenon was first investigated for using DPA in an assay for terbium by Barela and Sherry.[9]
Simple substituted pyridines vary significantly in environmental fate characteristics, such as volatility, adsorption, and biodegradation.[10] Dipicolinic acid is among the least volatile, least adsorbed by soil, and most rapidly degraded of the simple pyridines.[11] A number of studies have confirmed dipicolinic acid is biodegradable in aerobic and anaerobic environments, which is consistent with the widespread occurrence of the compound in nature.[12] With a high solubility (5g/liter) and limited sorption (estimated Koc = 1.86), utilization of dipicolinic acid as a growth substrate by microorganisms is not limited by bioavailability in nature.[13]