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“O-PTIR spectral data from the E. coli MG1655 strain cultured in M9 minimal medium with various heavy isotopes exhibited a significant resemblance to the FT-IR findings. This highlighted the reproducibility of O-PTIR to track the incorporation of heavy isotopes into bacterial cells at the single-cell level.”
Reporting in Spectrochimica Acta Part A, researchers at University of Liverpool have achieved a significant breakthrough in microbial metabolism studies using stable isotope probing (SIP) combined with infrared spectroscopy.
The challenge of associating specific metabolic functions with individual bacteria in complex microbial communities has long limited our understanding of ecosystem dynamics and biotechnological applications. Traditional approaches often require prolonged incubation periods and lack the spatial resolution needed for single-cell analysis.
The research team employed various combinations of heavy stable isotopes (D, ¹³C, ¹⁵N, and ¹⁸O) with both FT-IR and O-PTIR spectroscopy to evaluate isotopic spectral shifts in E. coli bacteria.
The study revealed substantial spectral shifts in primary vibrational peaks due to heavy isotope incorporation, with deuterium incorporation into amide groups causing shifts in amide A and B peaks into the silent region. Remarkably, ¹³C and deuterium incorporation was detected within just 30 minutes of incubation, demonstrating rapid metabolic labeling kinetics.
The O-PTIR measurements at the single-cell level showed exceptional reproducibility and spectral quality compared to bulk FT-IR analysis. The technique successfully identified distinct C-D signature peaks across all deuterium-containing conditions and tracked isotopic shifts in amide I, amide II, carboxylate, and nucleic acid regions.
Time-course studies using PC-DFA analysis demonstrated clear clustering patterns based on isotope incorporation, validating the quantitative capabilities of the approach.
O-PTIR spectroscopy emerges as a transformative tool for single-cell metabolic analysis, offering submicron spatial resolution while maintaining the spectral fidelity of traditional infrared techniques.
The ability to track isotope incorporation kinetics in real-time at the cellular level opens new possibilities for antimicrobial resistance detection, environmental monitoring, and personalized medicine applications, positioning O-PTIR as an essential technique for advancing our understanding of microbial metabolism and community dynamics.
Sahand Shams
Centre for Metabolomics Research, University of Liverpool
DOI: 10.1016/j.saa.2024.125374
