Photobleaching of the Raman Spectroscopic Signature of Life and Mitochondrial Activity in Rho- Budding Yeast Cells

Raman spectra of mitochondria in single living budding yeast (zygote of Saccharomyces cerevisiae and Saccharomyces bayanus) cells have been measured and compared for two types of tetraploid strains, the wild-type strain and the rho(-) strain. The Raman spectroscopic signature of life, a strong Raman band at 1602 cm(-1) that sharply reflects the mitochondrial activity, has been found in both of the two strains with similar intensities. This signature showed photobleaching under irradiation of the 632.8 nm line of a He-Ne laser, only for the rho(-) strain. The photobleaching recovered by keeping the cell in the dark for two hours without laser irradiation. These findings indicate that the molecular species that gives rise to the 1602 cm(-1) band is an intermediate formed and accumulated during the metabolic cycle and that it absorbs at 632.8 nm to undergo photodecomposition. We also found a number of weak Raman bands in the 400-1200 cm(-1) region that show the same temporal behaviors as that of the 1602 cm(-1) band by an SVD analysis of time-resolved Raman spectra, Several new pieces of information oil the origin of the Raman spectroscopic signature of life have thus been obtained.