The responses of the obligate psychrophilic alga Chlamydomonas sp. UWO241 to temperature stress

The Antarctic alga Chlamydomonas sp. UWO241 is an obligate psychrophile that thrives in the cold but is unable to survive at moderate, seemingly innocuous temperatures. We dissect the responses of UWO241 to temperature stress using global transcriptomic approaches. We demonstrate that slow growth at low temperatures is not a hallmark of stress, but a result of a unique psychrophilic cell physiology and a permanently re-routed steady-state metabolism. UWO241 constitutively accumulates high levels of protective metabolites including soluble sugars, polyamines and antioxidants at a range of steady-state temperatures. In contrast, the model mesophile Chlamydomonas reinhardtii accumulates these metabolites only during cold stress. A shift from 4C to 24C dramatically alters the UWO241 transcriptome but we demonstrate that this functional heat stress response is attenuated compared to C. reinhardtii exposed to comparable conditions. We suggest that differences in perception of and a globally attenuated response to heat are reasons for the sensitivity of psychrophiles to increased temperatures. Our work adds to the growing body of research on temperature stress in psychrophiles, many of which are threatened by climate change.