Constitutively Up-regulated Carbon Metabolism is an Adaptation to Low
Temperature in the Antarctic Psychrophile Chlamydomonas sp.
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 metabolomic approaches. UWO241
exhibits slow growth at 4°C, a temperature closest to its natural
habitat, and faster growth at higher temperatures of 10-15°C. We
demonstrate that the slower growth-rate characteristic of UWO241 at 4⁰C
is not necessarily a hallmark of stress. UWO241 constitutively
accumulates high levels of protective metabolites including soluble
sugars, polyamines and antioxidants at a range of steady-state
temperatures. In contrast, the mesophile Chlamydomonas reinhardtii
accumulates these metabolites only during cold stress. Despite low
growth rates, 4°C-grown UWO241 cultures had a higher capacity to respond
to heat stress (24°C) and accumulated increased amounts of antioxidants,
lipids and soluble sugars, when compared to cultures grown at 10-15°C.
We conclude that the slower growth rate and the unique psychrophilic
physiological characteristic of UWO241 grown at 4⁰C result in a
permanently re-routed steady-state metabolism, which contributes to its
increased resistance to heat stress. Our work adds to the growing body
of research on temperature stress in psychrophiles, many of which are
threatened by climate change.