Raman spectral analysis of microbial pigment compositions in vegetative cells and heterocysts of multicellular cyanobacterium

Single-cell pigment analysis of phototrophic and phyllosphere bacteria using simultaneous detection of Raman and autofluorescence spectra

Microbes produce various types of pigments that are essential for their biological activities. Microbial pigments are important for humans because they are used in the food industry and medicine. The visualization and evaluation of the pigment diversity of microbial cells living in natural environments will contribute not only to the understanding of their ecophysiology but also to the screening of useful microbes. Here, we demonstrate the simultaneous, nondestructive detection of the resonance Raman and autofluorescence spectra of pigments in model purple phototrophic bacteria at the single-cell level. The single-cell Raman spectra measured using confocal laser Raman microspectroscopy with 632.8 nm excitation covered the wavenumber range of 660-3,022 cm-1 (corresponding to 661-783 nm), in which the autofluorescence spectra from the pigments can be detected simultaneously as a baseline. The peak position of the resonance Raman spectra of the carotenoids in the cells provided information on the length of the polyene chain and structural characteristics, such as conjugated keto groups and terminal rings. By contrast, the extracted autofluorescence spectra of purple phototrophic bacteria differed in pattern depending on bacteriochlorophyll type (a or b), suggesting that their autofluorescence originates from bacteriochlorophyll-related molecules. In addition, we revealed the pigment diversity in microbial cells on the leaf surface and isolated pigmented bacteria that could contribute to the pigment diversity of the environmental sample. Our study shows that Raman and fluorescence microspectroscopy is a useful tool for finding novel pigmented microbes and uncovering yet unknown relationships between microbes and light.IMPORTANCETo understand the activities of microbes in natural environments, it is important to know the types of biomolecules they express in situ. In this study, we report a method using resonance Raman and autofluorescence signatures to detect and distinguish the types of carotenoid and bacteriochlorophyll pigments in intact, living cells. We have shown that this method can be used to estimate the expression status and pigment types in purple phototrophic bacteria and carotenoid-producing bacteria as well as the diversity of the pigments expressed by microbes on the leaf surface. Our method requires little pretreatment and can analyze pigments without destroying cells, making it a useful tool for visualizing phototrophic activity and searching for unidentified microbes.

The crucial role played by material trace analysis in resolving a murder vs. suicide dilemma

In the case of a young woman's death by falling from the window of her boyfriend's sixth-floor apartment, investigators needed to determine whether the fall was suicidal or if the victim was forcibly pushed. The incident occurred at night, with her boyfriend being the only witness to how the fall happened. Establishing the origin of the material traces found on the woman's stockings and shoes, along with other clues, played a crucial role in resolving this dilemma. The traces found on the stockings and samples collected from the building's external wall were analyzed using digital stereomicroscopy, High-resolution scanning electron microscopy (HRSEM) coupled with energy dispersive X-ray spectroscopy (EDX), and optical microscopy. Chlorophyll presence on both the victim's stockings and the surface of the building façade was confirmed using Raman spectroscopy. The inorganic traces found on the shoes and the external wall were examined using stereomicroscopy and HRSEM coupled with EDX and were found to be similar in texture and elemental composition. The correspondence between the biological structures and mineral fragments, along with the dynamic friction marks found on the woman's body and shoes, confirmed physical contact between the victim and the external wall. These findings led to the conclusion that the victim struggled for her life and the fall resulted from a criminal act.

Integration of Fluorescence Spectroscopy into a Photobioreactor for the Monitoring of Cyanobacteria

Phytoplankton are essential to aquatic ecosystems but can cause harmful algal blooms (HABs) that threaten water quality, aquatic life, and human health. Developing new devices based on spectroscopic techniques offers a promising alternative for rapid and accurate monitoring of aquatic environments. However, phytoplankton undergo various physiological changes throughout their life cycle, leading to alterations in their optical properties, such as autofluorescence. In this study, we present a modification of a low-cost photobioreactor designed to implement fluorescence spectroscopy to analyze the evolution of spectral signals during phytoplankton growth cycles. This device primarily facilitates the characterization of changes in autofluorescence, providing valuable information for the development of future spectroscopic techniques for detecting and monitoring phytoplankton. Additionally, real-time testing was performed on cyanobacterial cultures, where changes in autofluorescence were observed under different conditions. This work demonstrates a cost-effective implementation of spectroscopic techniques within a photobioreactor, offering a preliminary analysis for the future development of functional field devices for monitoring aquatic ecosystems.

Analysis of fate determination of vegetative cells with reduced phycocyanin content in a multicellular cyanobacterium using Raman microscopy

The one-dimensional multicellular cyanobacterium Anabaena sp. PCC 7120 exhibits two different cell types under nitrogen-deprived conditions. We found that the intensity of the Raman band at 1,629 cm -1 , which is associated with phycocyanin, was higher in undifferentiated cells (vegetative cells) than in differentiated cells (heterocysts). We observed cells whose band intensity at 1,629 cm -1 was statistically lower than that of vegetative cells, and named them "proheterocysts". We found that proheterocysts did not necessarily differentiate, and could divide or revert to being vegetative cells, as defined by having a higher band intensity at 1,629 cm -1 .

Pilot SERS Monitoring Study of Two Natural Hypersaline Lake Waters from a Balneary Resort during Winter-Months Period

Water samples from two naturally hypersaline lakes, renowned for their balneotherapeutic properties, were investigated through a pilot SERS monitoring program. Nanotechnology-based techniques were employed to periodically measure the ultra-sensitive SERS molecular characteristics of the raw water-bearing microbial community and the inorganic content. Employing the Pearson correlation coefficient revealed a robust linear relationship between electrical conductivity and pH and Raman and SERS spectral data of water samples, highlighting the interplay complexity of Raman/SERS signals and physicochemical parameters within each lake. The SERS data obtained from raw waters with AgNPs exhibited a dominant, reproducible SERS feature resembling adsorbed β-carotene at submicromole concentration, which could be related to the cyanobacteria-AgNPs interface and supported by TEM analyses. Notably, spurious SERS sampling cases showed molecular traces attributed to additional metabolites, suggesting multiplexed SERS signatures. The conducted PCA demonstrated observable differences in the β-carotene SERS band intensities between the two lakes, signifying potential variations in picoplankton abundance and composition or environmental influences. Moreover, the study examined variations in the SERS intensity ratio I245/I1512, related to the balance between inorganic (Cl--induced AgNPs aggregation) and organic (cyanobacteria population) balance, in correlation with the electrical conductivity. These findings signify the potential of SERS data for monitoring variations in microorganism concentration, clearly dependent on ion concentration and nutrient dynamics in raw, hypersaline water bodies.

Position-dependent changes in phycobilisome abundance in multicellular cyanobacterial filaments revealed by Raman spectral analysis

The one-dimensional filamentous cyanobacterium, Anabaena sp. PCC 7120, shows a simple morphological pattern consisting of two distinct cell types under nitrogen-deprived conditions. We found that microbial pigment composition in differentiated (heterocyst) and undifferentiated cells (vegetative cells) can be distinguished using Raman microscopy. The Raman bands associated with phycocyanin and allophycocyanin were of higher intensity in vegetative cells than those in heterocysts. However, these bands had statistically lower intensity in vegetative cells located further away from heterocysts. That is, the pigment composition in individual cells is affected by locational information in a filament.