Accurate delivery of chemicals to a small target using a pressure-driven valved micropipette.

We describe a new method for accurately and reproducibly delivering a minute amount of a chemical to a small target in an aqueous environment. Our method is based on a micropipette with a check valve at its tip that can be opened and closed on demand. We demonstrate that this device can produce a flux of 10 l in a short pulse lasting less than 100 ms.

Bacterial cell-body rotation driven by a single flagellar motor and by a bundle.

Using self-trapped Escherichia coli bacteria that have intact flagellar bundles on glass surfaces, we study statistical fluctuations of cell-body rotation in a steady (unstimulated) state. These fluctuations underline direction randomization of bacterial swimming trajectories and plays a fundamental role in bacterial chemotaxis. A parallel study is also conducted using a classical rotation assay in which cell-body rotation is driven by a single flagellar motor.

Rotating Bacteria on Solid Surfaces without Tethering.

Bacterial motion is strongly affected by the presence of a surface. One of the hallmarks of swimming near a surface is a defined curvature of bacterial trajectories, underlining the importance of counter rotations of the cell body and flagellum for locomotion of the microorganism. We find that there is another mode of bacterial motion on solid surfaces, i.