Microstome - macrostome transformation in the polymorphic ciliate Tetrahymenavorax leads to mechanosensitivity associated with prey-capture behaviour

摘要

Ciliates feed by phagocytosis. Some ciliate species, such as Tetrahymena vorax, are polymorphic, a strategy that provides moreflexible food utilization. Cells of the microstomal morph of T. vorax feed on bacteria, organic particles and organic solutes in anon-selective manner, whereas macrostome cells are predators that consume specific prey ciliates. In the present study, weinvestigated a possible correlation between phagocytosis and mechanosensitivity in macrostome T. vorax. Microstome cellsseem to be insensitive to mechanical stimulation whereas macrostome cells depolarise in response to mechanical stimulation ofthe anterior part of the cell. The amplitude of the receptor potential induced by either a prey ciliate or a 5 mu m push by a glassneedle was sufficient to elicit a regenerative Ca~(2+) spike. The difference in mechanosensitivity of the two forms correlates with the swimming behaviour when hitting an obstacle; microstome cells swim alongside the obstacle whereas macrostome cells swimbackwards, turn and resume forward swimming. Macrostome cells prevented from backward swimming and the subsequent turnfailed to capture prey cells in their pouch. Macrostome cells consumed heterospecific prey ciliates preferentially over conspecificmicrostome cells. This selectivity is not due to electrical membrane responses elicited by physical contact. Both microstome andmacrostome cells accumulated in an area containing putative substances released from heterospecific prey ciliates, but thesubstances did not elicit any electrophysiological membrane responses. We conclude that the mechanosensitivity of macrostomecells is associated with the prey-capture behaviour, whereas the selective phagocytosis is probably due to chemo-attraction toheterospecific prey ciliates.