Metabolic Adaptation of a Globally Important Diatom following 700 Generations of Selection under a Warmer Temperature

Diatoms, accounting for 40% of the
marine primary production and
20% of global carbon dioxide fixation, are threatened by the ongoing
ocean warming (OW). However, whether and how these ecologically important
phytoplankton adapt to OW remains poorly unknown. Here, we experimentally
examined the metabolic adaptation of a globally important diatom species Skeletonema dohrnii (S. dohrnii) to OW at two elevated temperatures (24 and 28 °C compared
with 20 °C) under short-term (∼300 generations) and long-term
(∼700 generations) selection. Both warming levels significantly
increased the cell growth rate but decreased the chlorophyll a content. The contents of particulate organic carbon (POC)
and particulate organic nitrogen (PON) decreased significantly initially
(i.e., until 300 generations) at two temperature treatments but completely
recovered after 700 generations of selection, suggesting that S. dohrnii ultimately developed thermal adaptation.
Proteomic analysis demonstrated that elevated temperatures upregulated
energy metabolism via glycolysis, tricarboxylic acid cycle, and fatty
acid oxidation as well as nitrogen acquisition and utilization, which
in turn reduced substance storage because of trade-off in the 300th
generation, thus decreasing POC and PON. Interestingly, populations
at both elevated temperatures exhibited significant proteome plasticity
in the 700th generation, as primarily demonstrated by the increased
lipid catabolism and glucose accumulation, accounting for the recovery
of POC and PON. Changes occurring in cells at the 300th and 700th
generations demonstrate that S. dohrnii can adapt to the projected OW, and readjusting the energy metabolism
is an important adaptive strategy.