The infrared spectra of Bacillus bacteria part I: vegetative Bacillus versus sporulated cells and the contributions of phospholipids to vegetative infrared spectra

Label-Free Identification of Spore-Forming Bacteria Using Ultrabroadband Multiplex Coherent Anti-Stokes Raman Scattering Microspectroscopy

Spore-forming bacteria accumulate dipicolinic acid (DPA) to form spores to survive in extreme environments. Vibrational spectroscopy is widely used to detect DPA and elucidate the existence of the bacteria, while vegetative cells, another form of spore-forming bacteria, have not been studied extensively. Herein, we applied coherent anti-Stokes Raman scattering (CARS) microscopy to spectroscopically identify both spores and vegetative cells without staining or molecular tagging. The spores were identified by the strong CARS signals due to DPA. Furthermore, we observed bright spots in the vegetative cells in the CARS image at 1735 cm^-1. The vegetative cells contained molecular species with C=O bonds because this vibrational mode was associated with the carbonyl group. One of the candidate molecular species is diketopimelic acid (DKP), a DPA precursor. This hypothesis was verified by comparing the spectrum obtained by the vegetative cells with that of the DKP analogue (ketopimelic acid) and with the result obtained by DFT calculation. The results indicate that the observed vegetative cell is in the sporulation process. CARS spectra can be used to monitor the maturation and preformation of spores.

Domain-level Identification of Single Prokaryotic Cells by Optical Photothermal Infrared Spectroscopy

Infrared spectroscopy is used for the chemical characterization of prokaryotes. However, its application has been limited to cell aggregates and lipid extracts because of the relatively low spatial resolution of diffraction. We herein report optical photothermal infrared (O-PTIR) spectroscopy of prokaryotes for a domain-level diagnosis at the single-cell level. The technique provided infrared spectra of individual bacterial as well as archaeal cells, and the resulting aliphatic CH3/CH2 intensity ratios showed domain-specific signatures, which may reflect distinctive cellular lipid compositions; however, there was interference by other cellular components. These results suggest the potential of O-PTIR for a domain-level diagnosis of single prokaryotic cells in natural environments.

Spectroscopy and viability of Bacillus subtilis spores after ultraviolet irradiation: implications for the detection of potential bacterial life on Europa

One of the most habitable environments in the Solar System outside of Earth may exist underneath the ice on Europa. In the near future, our best chance to look for chemical signatures of a habitable environment (or life itself) will likely be at the inhospitable icy surface. Therefore, it is important to understand the ability of organic signatures of life and life itself to persist under simulated europan surface conditions. Toward that end, this work examined the UV photolysis of Bacillus subtilis spores and their chemical marker dipicolinic acid (DPA) at temperatures and pressures relevant to Europa. In addition, inactivation curves for the spores at 100 K, 100 K covered in one micron of ice, and 298 K were measured to determine the probability for spore survival at the surface. Fourier transform infrared spectra of irradiated DPA showed a loss of carboxyl groups to CO2 as expected but unexpectedly showed significant opening of the heterocyclic ring, even for wavelengths>200 nm. Both DPA and B. subtilis spores showed identical unknown spectral bands of photoproducts after irradiation, further highlighting the importance of DPA in the photochemistry of spores. Spore survival was enhanced at 100 K by ∼5× relative to 298 K, but 99.9% of spores were still inactivated after the equivalent of ∼25 h of exposure on the europan surface.

Distinction of broken cellular wall Ganoderma lucidum spores and G. lucidum spores using FTIR microspectroscopy

In this paper, FTIR microspectroscopy was used to identify broken cellular wall Ganoderma lucidum spores and G. lucidum spores. For IR spectra, broken cellular wall G. lucidum spores and G. lucidum spores were mainly different in the regions of 3000-2800, 1660-1600, 1400-1200 and 1100-1000 cm(-1). For curve fitting, the results showed the differences in the protein secondary structures and the polysaccharide structures/content between broken cellular wall G. lucidum spores and G. lucidum spores. Moreover, the value of A1078/A1741 might be a potentially useful factor to distinguish broken cellular wall G. lucidum spores from G. lucidum spores. Additionally, FTIR microspectroscopy could identify broken cellular wall G. lucidum spores and G. lucidum spores accurately when it was combined with hierarchical cluster analysis. The result suggests FTIR microspectroscopy is very simple and efficient for distinction of broken cellular wall G. lucidum spores and G. lucidum spores. The result also indicates FTIR microspectroscopy may be useful for TCM identification.

A study of Ganoderma lucidum spores by FTIR microspectroscopy

In order to obtain unique information of Ganoderma lucidum spores, FTIR microspectroscopy was used to study G. lucidum spores from Anhui Province (A), Liaoning Province (B) and Shangdong Province (C) of China. IR micro-spectra were acquired with high-resolution and well-reproducibility. The IR spectra of G. lucidum spores from different areas were similar and mainly made up of the absorption bands of polysaccharide, sterols, proteins, fatty acids, etc. The results of curve fitting indicated the protein secondary structures were dissimilar among the above G. lucidum spores. To identify G. lucidum spores from different areas, the H1078/H1640 value might be a potentially useful factor, furthermore FTIR microspectroscopy could realize this identification efficiently with the help of hierarchical cluster analysis. The result indicates FTIR microspectroscopy is an efficient tool for identification of G. lucidum spores from different areas. The result also suggests FTIR microspectroscopy is a potentially useful tool for the study of TCM.

The infrared spectra of Bacillus bacteria part II: sporulated Bacillus--the effect of vegetative cells and contributions of calcium dipicolinate trihydrate, CaDP.3H2O

Our previous paper showed that certain infrared (IR) peaks, e.g., the peak at 1739 cm(-1), are due to varying (trace) amounts of vegetative cells amongst the Bacillus spores and that these and other vegetative bands are associated with lipid-soluble compounds, likely an ester or phospholipid. This work investigates the infrared spectra of eight different sporulated Bacillus bacteria. For the endospores it is observed that peaks at 1441, 1277, and 1015 cm(-1) along with a distinct quartet of peaks at 766, 725, 701, and 659 cm(-1) are clearly associated with calcium dipicolinate trihydrate, CaDP.3H2O. It is emphasized that the spore peaks, especially the quartet, arise from the calcium dipicolinate trihydrate and not from dipicolinic acid or other dipicolinate hydrate salts. The CaDP.3H2O infrared peaks and the effects of hydration are studied using quantum chemistry in the PQS software package. The quartet is associated with many modes including contributions from the Ca2+ counterion and hydration waters including Ca-O-H bends, H2O-Ca-O torsions, and O-C-O bends. The 1441 and 1015 cm(-1) modes are planar pyridine modes with the 1441 cm(-1) mode primarily a ring C-N stretch and the 1015 cm(-1) mode primarily a ring C-C stretch.