A microfluidic platform for profiling biomechanical properties of bacteria

Abstract

The ability to resist mechanical forces is necessary for the survival and division of bacteria and has traditionally been probed using specialized, low-throughput techniques such as atomic force microscopy and optical tweezers. Here we demonstrate a microfluidic technique to profile the stiffness of individual bacteria and populations of bacteria. The approach is similar to micropipette aspiration used to characterize the biomechanical performance of eukaryotic cells. However, the small size and greater stiffness of bacteria relative to eukaryotic cells prevents the use of micropipettes. Here we present devices with sub-micron features capable of applying loads to bacteria in a controlled fashion. Inside the device, individual bacteria are flowed and trapped in tapered channels. Less stiff bacteria undergo greater deformation and therefore travel further into the tapered channel. Hence, the distance traversed by bacteria into a tapered channel is inversely related to cell stiffness. We demonstrate the ability of the device to characterize hundreds of bacteria at a time, measuring stiffness at 12 different applied loads at a time. The device is shown to differentiate between two bacterial species, E. coli (less stiff) and B. subtilis (more stiff), and detect differences between E. coli submitted to antibiotic treatment from untreated cells of the same species/strain. The microfluidic device is advantageous in that it requires only minimal sample preparation, no permanent cell immobilization, no staining/labeling and maintains cell viability. Our device adds detection of biomechanical phenotypes of bacteria to the list of other bacterial phenotypes currently detectable using microchip-based methods and suggests the feasibility of separating/selecting bacteria based on differences in cell stiffness.

Mechanical stress compromises multicomponent efflux complexes in bacteria

“…A microfluidic device was used to mechanically stimulate individual bacteria 17 . Six devices were placed onto each fabricated wafer (Extended Data Fig.…”

“…To query the individual contributions of each form of mechanical stress, we used a microfluidic device with submicron features to apply mechanical loads to individual bacteria. The device is analogous to micropipette aspiration commonly used to study mammalian cell biomechanics 15,16 but instead of pulling the cell into a tapered channel, the device forces cells into tapered channels using fluid pressure 17 . Each device contains sets of tapered channels to apply twelve distinct magnitudes of pressure difference (Δ P ) across the trapped bacteria within a single experiment (Fig.…”

Nano and Microtechnologies for the Study of Magnetotactic Bacteria

“…[107] Microfluidic platforms have also been developed to investigate differences in the stiffness and deformability of bacterial cells such as E. coli and their resistance to antibiotics. [108] These platforms offer much higher throughput than conventional tools like optical tweezers and atomic force microscopy. [108] Similar devices can be used to understand whether MTB with different numbers of magnetosomes have different stiffness, which may enable high throughput isolation of subpopulations of interest using deformability-based cell cytometry.…”

Mechanics and stability of vesicles and droplets in confined spaces

“…Quantitative observations of particle deformation in narrow pores [21] and micropipettes [54] have traditionally been used as a method to indirectly measure their physical properties. We here concentrate on micropipette aspiration for which standard experiments and modeling efforts have focused on cylindrical pipettes with constant cross sections.…”

“…This technique is now considered as a standard [18] for quantifying the mechanics of a variety of particles including cells [19] and vesicles [20]. Variations of this strategy have also been proposed, including, for instance, the use of conical microchannels to determine the elastic properties of bacteria based on their equilibrium position under a pressure gradient [21]. …”