Calcium dipicolinate

With the exception of some constituents such as high concentrations of calcium, dipicolinic aci d, and in Bacillus sphaericus, a, E-diaminopimelic acid, spore are similar to the vegetative cells in composition. 

The basis of phenotypic discrimination of closely related species via Raman spectroscopy lies in its sensitivity to the intracellular molecular components including extrachromosomally encoded phenotypes, such as the Bacillus anthracis or B. thuringiensis toxins or polyglutamic acid capsules. Other prominent examples are cell storage materials like the polyhydroxy butyric acid (PHB), carotenoid-based pigments like sarcinaxanthin, hemoproteins like cytochrome or calcium dipicolinate (CaDPA). Raman spectra of single bacteria, in which the latter four intracellular substances occur, are shown in... 

Fig. 19.2. Micro-Raman spectra of different single bacterial cells normal bacterial Raman spectrum of Staph, wameri compared to Raman spectra with enhanced amounts of subcellular components calcium dipicolinate for a spore of B. pumilus polyhydroxy butyric acid (PHB) in B. megaterium cytochrome in Staph, cohnii and sarcina xanthin in M. luteus...

The marker substance for Bacillus endospores is calcium dipicolinate (CaDPA). One approach is the isolation of CaDPA from a minimal amount of spores and its subsequent identification by SERS spectroscopy [97]. The detection of CaDPA in endospores was used for the detection of minimal amount of spores [98] even in automated mail sorting systems [99]. The detection of CaDPA does not give any information about the Bacillus species present. The investigation of the components in the outmost layers of the endospores, the outer sporecoat, or the exosporium will lead to more precise information,... 

Bacterial spore walls are like cell walls, but surrounded by a calcium dipicolinate complex, exterior to which is a protein shell, rich in disulfide bonds (Gould and Hitchins, 1963). 

Under certain circumstances, many bacteria produce capsules outside their ceU envelopes. Capsules are usually made of polysaccharide however, some Bacillus capsules are composed of D-glutamic acid polypeptide. Certain Gram positive bacteria, most notably strains of Bacillus and Clostridium, produce modified ceUs (endospores) capable of surviving in adverse environments. Spore PG is found between an inner and outer membrane and differs from that in the normal vegetative cell muramic acid is mostly in the lactam form the spore PG has fewer peptide cross-links and the ceU exterior is coated with keratin. The spore also contains large quantities of calcium dipicolinate, a substance involved in microbial heat resistance. 

In general, lanthanide-based sensors have strongly attracted the attention of the scientific community worldwide for some decades due to their unique and outstanding photophysical characteristics such as long emission lifetimes, very narrow emission bands and large Stoke shifts. These spectroscopic features allow time resolved detection that is the most elegant way to clear measurements from background fluorescence with a consequent remarkable sensitivity enhancement. As already mentioned in Sect. 3.1.1.1 [120], DPA or better calcium dipicolinate... 

C7H8Ni,S, 4-Formylpyridine thiosemicarbazone, 35B, 166 C7H8NaSe, 2-Formylpyridine selenosemicarbazone, 38B, 261, 354 C7H9CaN07, Calcium dipicolinate trihydrate, 33B, 113 C7H9CIN2O, 1-Methylnicotinamide chloride, 40B, 545 C7H9CIN1, N,N-Dimethyl-N -(6-chloropyridazinyl-3) formamidine, 40B, 223... 

Figure 4. Conventional micro-Raman spectra of individual bacillus spores (a). The spectra are nearly identical due to the large content of calcium dipicolinate in the core of the spores. When silver nanoparticles are adsorbed to the surface of the spores (b), the spectra change significantly. The spectra are no longer dominated by the calcium dipicolinate (dashed lines).

The rapid and accurate identification of biomoleclues is vital for first responders in the event of a biological attack, as well as for patients with a need to monitor chronic or acute conditions. In this chapter, we outline the use of surface-enhanced Raman spectroscopy (SERS) for the detection of calcium dipicolinate (CaDPA), a biomarker for anthrax, and glucose, an indicator for diabetes. 

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