Cell proliferation of Paramecium tetraurelia under clinorotation

It has been reported that Paramecium proliferates faster under microgravity in space, and slower under hypergravity (Kato et al., 2003). Effects of gravity on cell proliferation could be discussed in terms of energetics of swimming. Because of the characteristics of 'gravikinesis' as well as 'gravitaxis', Paramecium would decrease the energy expenditure under microgravity and increase it under hypergravity. The larger stock of energy would enhance the proliferation under microgravity. In order to simulate the effect of microgravity, we investigated the proliferation under clinorotation. When cells were rotated at 2.5 rpm, the proliferation rate decreased. Similar but less pronounced decrease was also found under low speed clinorotation (0.2 rpm).