pH-taxis in choanoflagellates

GASTÓN L. MIÑO; MIMI A. R. KOEHL; NICOLE KING; ROMAN STOCKER

Roscoff

Congreso; 2015 International Choanoflagellate Workshop; 2015

CNRS

Choanoflagellates have multiple motility adaptations, ranging from very slow, random swimming of rosette colonies, to slow, solitary cells with a feeding collar, to the impressively fast and directional swimming of single cells with a reduced or absent collar. In particular, there is a striking difference in motility between single cells, which can be highly directional, and colonies, which have hardly any directionality at all. Motility gives cells the ability to migrate towards more favorable microenvironments, this process is called taxis (e.g., chemotaxis). We used microfluidics and video microscopy to demonstrate that choanoflagellates of the Salpingoeca rosetta species display strong chemotaxis along pH gradients, also called ´pH-taxis´. Specifically, we found that (i) only fast swimmers engage in this behavior, and (ii) the direction of the response is pH-dependent, going from negative pH-taxis (attraction to lower pH) at pH < 8, to positive pH-taxis (attraction to higher pH) when pH tends to 5. The ecological implications of seeking optimal pH conditions are as yet unclear, but the pervasive occurrence of pH gradients in bacterial biofilms suggests that pH taxis in choanoflagellates may be related to foraging on surface-attached bacteria.