The biomechanical role of extra-axonemal structures in shaping the flagellar beat of Euglena

Giancarlo Cicconofri; Giovanni Noselli; Antonio DeSimone

In order to put our hypothesis into context, we observe that the flagellar beat of PFR-bearing kinetoplastid organisms, such as Leishmania and Crithidia, is planar [9] . An apparent exception to beat planarity in kinetoplastids is found in the pathogenic parasite Trypanosoma brucei, which shows a characteristic non-planar "drill-like" motion [17] . However, Trypanosoma's flagellum is not free, like that of Leishmania and Crithidia, but it is attached to the organism for most of its length, wrapped helically around the cell body. According to [2] the flagellum-body mechanical interaction could alone explain Trypanosomes' distinctive motion. Confirming this conclusion, [34] showed that Trypanosoma mutants with body-detached flagellum generate fairly planar beating. It is conjectured that the PFR-Ax bonds operate as the 5-6 interdoublet links in Chlamydomonas and sperm cells, inhibiting MTs sliding and selecting a plane of beat [36] .