Dielectrophoretic analysis of the impact of isopropyl alcohol on the electric polarisability of Escherichia coli whole-cells

Abstract

Whole-cell biocatalysts are versatile tools in (industrial) production processes; though, the effects that impact the efficiency are not fully understood yet. One main factor that affects whole-cell biocatalysts is the surrounding medium, which often consists of organic solvents due to low solubility of substrates in aqueous solutions. It is expected that organic solvents change the biophysical and biochemical properties of the whole-cell biocatalysts, e.g. by permeabilising the cell membrane, and thus analysis of these effects is of high importance. In this work, we present an analysis method to study the impact of organic solvents on whole-cell biocatalysts by means of dielectrophoresis. For instance, we evaluate the changes of the characteristic dielectrophoretic trapping ratio induced by incubation of Escherichia coli, serving as a model system, in an aqueous medium containing isopropyl alcohol. Therefore, we could evaluate the impact on the electric polarisability of the cells. For this purpose, a special microchannel device was designed and Escherichia coli cells were genetically modified to reliably synthesise a green fluorescent protein. We could demonstrate that our method was capable of revealing different responses to small changes in isopropyl alcohol concentration and incubation duration. Complementary spectrophotometric UV-Vis (ultraviolet-visible light) absorbance analysis of released NAD(P) + /NAD(P)H cofactor and proteins confirmed our results. Based on our results, we discuss the biophysical effects taking place during incubation.

Analysis of microorganisms with nonlinear electrokinetic microsystems

“…and images of non‐trapped and trapped cells respectively. Reprinted from [37], open access article under Creative Commons CC BY license (2020).…”

“…Examination of pathogenic bacteria is of vital importance since bacterial species continually affect millions of humans around the world due to their persistent, hardy nature and their ability to develop antibiotic resistance [67,68]. A great example of this is E. coli capable of multiplying quickly within the body and has slowly mutated and evolved to circumvent physiological barriers [37,68]. Just as the field of medicine advances, so do the bacterial species, challenging scientists to create more innovative and alternative solutions [43,69].…”

“…Epping et al. studied the impact of isopropyl alcohol (IPA) in an E. coli model, revealing changes in the dielectrophoretic trapping of the cells caused by the effect of the alcohol on cell polarizability [37]. The Viefhues group characterized an E. coli sample in its normal state to determine a reference point for the cell's migration and trapping patterns in a channel with a dense insulating post array (Fig.…”

“…Their method was able to identify distinct cells’ responses to small changes in IPA concentration. The group used pressure‐driven flow and superimposed a DEP force by applying an AC voltage for 30 s to observe the cells’ response; this reference standard was used as the basis for [37]. Two distinct responses were visible: the first was a higher voltage being needed to trap 50% of E. coli after incubation in 5% IPA for 5 minutes.…”

“…Two distinct responses were visible: the first was a higher voltage being needed to trap 50% of E. coli after incubation in 5% IPA for 5 minutes. An explanation was that lowered polarizability was due to leaking promoted by the diffusion of interior cellular ions and cofactors into the surrounding cytoplasm [37]. The second phenomenon was similar to the first but opposite as cells incubated in 10 or 15% IPA experienced an increase in polarizability.…”