The positive correlation between maximal growth rate
and thermal breadth of marine phytoplankton, which holds
both within and among phyla, suggests that fast-growing
species have the capacity to tolerate a wider range of temperatures.
One possible explanation might be that the
growth rate is determined by the concentrations of the ratelimiting
enzymes [e.g. the ribulose-1,5-bisphosphate carboxylase/
oxygenase (RubisCO) enzyme]. A fast-grower tends
to have higher concentrations of the key enzyme. Compared
with the slower growers, even if the same proportion of the
enzyme is denatured at extreme temperatures, it still has
more enzymes to support positive growth.