Understanding UV-driven metabolism in the hypersaline ciliate Fabrea salina

By using NMR spectroscopy, a non-invasive investigation technique, we performed in vivo experiments aimed at uncovering the metabolic pathways involved in the early response of Fabrea salina cells to ultraviolet (UV) radiation. This hypersaline ciliate was chosen as a model organism because of its well-known high resistance to UV radiation. Identical cell samples were exposed to visible radiation only (control samples, CS) and to UV-B + UV-A + visible radiation (treated samples, TS), and NMR spectra of in vivo cells were collected at different exposure times. Resonances were identified through one and two-dimensional experiments. To compare experiments performed at variable irradiation times on different culture batches, metabolite signals affected by the UV exposure were normalized to corresponding intensity at tau = 0, the zero exposure time. The most affected metabolites are all osmoprotectants, namely, choline, glycinebetaine, betaines, ectoine, proline, a-trehalose and sucrose. The time course of these signals presents qualitative differences between CS and TS, and most of these osmoprotectants tend to accumulate significantly in TS in a UV dose-dependent manner. A picture of the immediate stress response of F. salina against UV radiation in terms of osmoprotection, water retention and salting-out prevention is described.