Microfluidic study of the chemotactic response ofEscherichia colito amino acids, signaling molecules and secondary metabolites

Abstract

Quorum sensing and chemotaxis both affect bacterial behavior on the population level. Chemotaxis shapes the spatial distribution of cells, while quorum sensing realizes a cell-density dependent gene regulation. An interesting question is if these mechanisms interact on some level: Does quorum sensing, a density dependent process, affect cell density itself via chemotaxis? Since quorum sensing often spans across species, such a feedback mechanism may also exist between multiple species. We constructed a microfluidic platform to study these questions. A flow-free, stable linear chemical gradient is formed in our device within a few minutes that makes it suitable for sensitive testing of chemoeffectors: we showed that the amino acid lysine is a weak chemoattractant for Escherichia coli, while arginine is neutral. We studied the effect of quorum sensing signal molecules of Pseudomonas aeruginosa on E. coli chemotaxis. Our results show that N-(3-oxododecanoyl)-homoserine lactone (oxo-C12-HSL) and N-(butryl)-homoserine lactone (C4-HSL) are attractants. Furthermore, we tested the chemoeffector potential of pyocyanin and pyoverdine, secondary metabolites under a quorum sensing control. Pyocyanin is proved to be a weak attractant while pyoverdine are repellent. We demonstrated the usability of the device in co-culturing experiments, where we showed that various factors released by P. aeruginosa affect the dynamic spatial rearrangement of a neighboring E. coli population, while surface adhesion of the cells is also modulated. V C 2015 AIP Publishing LLC. [http://dx

Quantitative analysis of the chemotaxis of a green alga, Chlamydomonas reinhardtii, to bicarbonate using diffusion-based microfluidic device

“…In this context, chemotaxis may provide a significant fitness advantage. 19 Since modern studies of bacterial chemotaxis, 20,21 the chemotactic responses of bacteria to a wide range of chemical substances, such as sugars, 17 amino acids, 22 and signaling molecules, 23 have been demonstrated. Chemotaxis of C. reinhardtii has been studied during the past few decades as well, but relatively less information is available for the chemotactic response of C. reinhardtii compared with other organisms (e.g., Escherichia coli).…”

“…Since microfluidics offers unprecedented level of controllability and stability, a precise manipulation of the fluidic properties, including the flow rate and the concentration, is possible. 23,25,26 Furthermore, the microscale approach enables the behavior analysis of microorganisms at the single-cell level. 27 Therefore, the microfluidic systems are considered to be highly suitable for the quantitative analysis of chemotactic response.…”

“…28,29 Even though the flow-based systems have several advantages, such as the capability of generating controllable and switchable gradients, 30 the flowing nature limits the period for assay and may hinder the chemotaxis-induced migration of cells. 23,26 Furthermore, the additional apparatus including syringe pumps and tubes are required to operate these systems, which cause inconveniences in system operation. 26 Compared to the flow-based devices, the diffusion-based devices generate the gradient between several fluids which are separated by physical barriers (i.e., semi-permeable membrane).…”

A hybrid microfluidic device for on-demand orientation and multidirectional imaging of C. elegans organs and neurons

“…46,47 By restricting convective flow with membranes or hydrogels while allowing diffusion of small molecules to generate chemical gradients, flow-free and diffusion-based static gradient generators are able to decouple cell motion of nonadherent cells from flow. 7,14,48 Further microbial behaviors are expected to be revealed with the spatial and temporal resolutions offered by these static gradient generator devices, the decoupling of cell migration completely from fluid flow, and the integration of theoretical simulation with experiments in controlled microfluidic environments to quantify the bacterial chemotaxis phenomena.…”

“…These problems suggest that a static, non-flowing gradient generator may be a more suitable platform for chemotaxis studies in the long run, despite posing greater difficulties in design, fabrication, and packaging. 7,12,[14][15][16] …”