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J. Bacteriol. doi:10.1128/JB.00282-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Levels of Ca²⁺-dipicolinic acid in individual Bacillus spores determined using microfluidic Raman tweezers

Department of Physics, East Carolina University, Greenville, NC 27858-4353; Biophysics Laboratory, Guangxi Academy of Sciences, Nanning, Guangxi 530003, P.R. China; Department of Molecular, Microbial and Structural Biology, University of Connecticut Health Center, Farmington, Connecticut 06030-3305

^* To whom correspondence should be addressed. Email: liy{at}mail.ecu.edu.

	Abstract

Pyridine-2,6-dicarboxylic acid (dipicolinic acid (DPA)) in a 1:1 chelate with calcium ion (Ca-DPA) comprises 5-15% of the dry weight of spores of Bacillus species. Ca-DPA is important in spore resistance to many environmental stresses and in spore stability, and Ca-DPA levels in spore populations can vary with spore species/strains, as well as with sporulation conditions. We have measured levels of Ca-DPA in large numbers of individual spores in populations of a variety of Bacillus species and strains using microfluidic Raman tweezers, in which a single spore is trapped in a focused laser beam and its Ca-DPA is quantitated from the intensity of the Ca-DPA-specific band at 1017 cm^-1 in Raman spectroscopy. Conclusions from these measurements include: 1) Ca-DPA concentrations in the spore core are >800 mM, well above Ca-DPA solubility; 2) SpoVA proteins may be involved in Ca-DPA uptake in sporulation; and 3) Ca-DPA levels differ significantly among individual spores in a population, but much of this variation could be due to variations in the sizes of individual spores.

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