Studies of bacterial aerotaxis in a microfluidic device

Abstract

Aerotaxis, the directional motion of bacteria in gradients of oxygen, was discovered in late 19th century and has since been reported in a variety of bacterial species. Nevertheless, quantitative studies of aerotaxis have been complicated by the lack of tools for generation of stable gradients of oxygen concentration, [O2]. Here we report a series of experiments on aerotaxis of Escherichia coli in a specially built experimental setup consisting of a computer-controlled gas mixer and a two-layer microfluidic device made of polydimethylsiloxane (PDMS). The setup enables generation of a variety of stable linear profiles of [O2] across a long gradient channel, with characteristic [O2] ranging from aerobic to microaerobic conditions. A suspension of E. coli cells is perfused through the gradient channel at a low speed, allowing cells enough time to explore the [O2] gradient, and the distribution of cells across the channel is analyzed near the channel outlet at a throughput of >105 cells per hour. Aerotaxis experiments are performed in [O2] gradients with identical logarithmic slopes and varying mean concentrations, as well as in gradients with identical mean concentrations and varying slopes. Experiments in gradients with [O2] ranging from 0 to ~11.5% indicate that, in contrast to some previous reports, E. coli cells do not congregate at some intermediate level of [O2], but rather prefer the highest accessible [O2]. The presented technology can be applied to studies of aerotaxis of other aerobic and microaerobic bacteria.

Chemotaxis of Escherichia coli to Norepinephrine (NE) Requires Conversion of NE to 3,4-Dihydroxymandelic Acid

“…Note that this response is highly unlikely to be an aerotactic response through Aer, as strains lacking a functional Tsr receptor did not show any response in the microfluidic assay. Moreover, the device is not designed to either generate or maintain gaseous gradients within the flow chamber, as has been reported by Adler et al (30). Chemotaxis to DHMA requires the Tsr chemoreceptor and its intact serine-binding site.…”

Osmotaxis in Escherichia coli through changes in motor speed

“…This behavior, called taxis [Krell et al, 2011, Purcell, 1977, has long been a subject of scientific investigation, as it serves a variety of purposes: seeking out nutrients and avoiding toxic substances Armitage, 2004, Adler, 1969], identifying thermal [Paster and Ryu, 2007] and oxygen [Adler et al, 2012] gradients, as well as aiding pathogenic species in infecting their hosts [Rivera-Chávez et al, 2013, Cullender et al, 2013. The understanding of bacterial taxis is not only important when it comes to bacterial motility and accumulation; it also serves as a model for biological signal processing.…”

Microfluidics Expanding the Frontiers of Microbial Ecology

“…In this case, one can take advantage of the gas permeability of PDMS to create steady oxygen gradients without the need for hydrogels or membranes (Adler et al 2010). This principle used by Adler et al (2012), who studied aerotaxis in E. coli under steady, linear profiles of oxygen ranging from microaerobic to aerobic conditions and showed that it does not obey log-sensing. Furthermore, the irreversible bonding that can be achieved between layers of PDMS, but not with hydrogels, makes aerotaxis an ideal model system for the study of microbial navigation in more realistic environments, such as when fluid flow is present.…”