Relations between growth rate, cell size, and DNA content in colpodean ciliates (ciliophora: Colpodea).

Optimal conditions for growth of 9 strains from 7 species of colpodean ciliates were determined using a factorial experimental design. Estimates of maximal growth rate were higher than those previously obtained for similar-sized ciliates. Using published cell size estimates, the slope of a cell size-growth rate relation was found to be not significantly different from zero, either when maximal growth rates were used or when all growth rates were scaled to 20°C, a suboptimal temperature. Both macronuclear DNA content and the ratio of macro- to micronuclear DNA were good predictors of maximal growth rate, but the ratio was not more predictive than macronuclear DNA content alone. The slope of the relation between minimum generation time and macronuclear DNA content was significantly less than that predicted by the skeletal-DNA theory of Cavalier-Smith. There was no significant relationship between gene concentration (measured as the ratio of macronuclear to micronuclear DNA, divided by cell volume) and maximal growth rate.