Using synchrotron FTIR spectromicroscopy to assess physiological and metabolic changes in photosynthetic mutants of <i>Chlamydomonas reinhardtii</i>

We utilized synchrotron Fourier-transform infrared spectromicroscopy to study photosynthetic mutants of the unicellular green algae Chlamydomonas reinhardtii. We were able to observe direct and knock-on effects of multiple mutations on the physiology and metabolism of individual living cells, and cleanly differentiate the spectra of cell lines that differed by a single point mutation. Phenotypic changes (direct or knock-on) included altered composition and relative abundance of storage and structural lipids, membrane compositions, relative abundance of photosynthetic and photoprotective pigments, abundance and structure of Photosystems I and II, and secondary structure of protein pools. In one mutant, the mutations combined to trigger cellular responses normally seen as cellular adaptation to ongoing high light stress, even under normal light conditions. We were further able to observe that one cell line had phenotypic changes indicative of knock-on physiological beyond those predicted by the point mutation itself.