Stable Isotope Probing
and Raman Spectroscopy for
Monitoring Carbon Flow in a Food Chain and Revealing Metabolic Pathway
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Abstract
Accurately measuring carbon flows is a challenge for
understanding
processes such as diverse intracellular metabolic pathways and predator-prey
interactions. Combined with stable isotope probing (SIP), single-cell
Raman spectroscopy was demonstrated for the first time to link the
food chain from carbon substrate to bacterial prey up to predators
at the single-cell level in a quantitative and nondestructive manner. <i>Escherichia coli</i> OP50 with different <sup>13</sup>C content,
which were grown in a mixture of <sup>12</sup>C- and fully carbon-labeled <sup>13</sup>C-glucose (99%) as a sole carbon source, were fed to the
nematode. The <sup>13</sup>C signal in <i>Caenorhabditis elegans</i> was proportional to the <sup>13</sup>C content in <i>E. coli</i>. Two Raman spectral biomarkers (Raman bands for phenylalanine at
1001 cm<sup>–1</sup> and thymine at 747 cm<sup>–1</sup> Raman bands), were used to quantify the <sup>13</sup>C content in <i>E. coli</i> and <i>C. elegans</i> over a range of
1.1–99%. The phenylalanine Raman band was a suitable biomarker
for prokaryotic cells and thymine Raman band for eukaryotic cells.
A biochemical mechanism accounting for the Raman red shifts of phenylalanine
and thymine in response to <sup>13</sup>C-labeling is proposed in
this study and is supported by quantum chemical calculation. This
study offers new insights of carbon flow via the food chain and provides
a research tool for microbial ecology and investigation of biochemical
pathways