Use of a microvalve-controlled microfluidic device in a chemotaxis assay of Tetrahymena pyriformis in response to amino acids released from bacteria

Abstract

In this study, we introduce a microfluidic device equipped with pneumatically-actuated valves, generating a linear gradient of chemoeffectors to quantify the chemotactic response of Tetrahymena pyriformis, a freshwater ciliate to amino acids excreted from bacteria. The microfluidic device was fabricated from an elastomer, polydimethylsiloxane (PDMS), using multi-layer soft lithography. The components of the device include electronically-controlled pneumatic microvalves, microchannels and microchambers. The linear gradient of the chemoeffectors was established by releasing a chemical from a ciliate-free microchamber into a microchamber containing the ciliate. The ciliate showed chemotactic behaviours by either swimming toward or avoiding the gradient. By counting the number of ciliate residing in each microchamber, we obtained a precise time-response curve. The ciliate in the microfluidic device were sensitive enough to be attracted to 0.1 femto-molar aspartate, suggesting that ciliates as a predator can track down food patches composed of a few bacterial cells. With the use of receptor inhibitors, such as tetraethyl ammonium (TEA) or the grape polyphenol resveratol, we have also demonstrated that the calcium signalling plays an important role in motility and following chemotactic behaviours.