Study of Bacterial Motility Using Optical Tweezers

Bacteria are arguably the simplest of known microorganisms, forming a fundamental part of the world we live in. Many functions they perform are found in scaled-up versions in higher organisms. Among many advanced functions, bacteria possess the ability to move in search for nutrients and favorable growth conditions. Measurement of the dynamical variables associated with bacterial swimming has proven to be difficult due to the lack of an accurate and convenient tool. In the past optical traps have been used for the manipulation of microscopic objects and measurement of minute forces. Herein, I have devised techniques for use of optical traps for direct measurement of the dynamics of bacterial swimming and chemotaxis, shedding light on the propulsion apparatus and sensory systems. A detailed analysis is performed to explore the effects of non-local hydrodynamic interactions on the swimming of single cells. Due to the lack of reliable measurement techniques, experimentalists often use theoretical models to estimate bacterial dynamics, the validity of which are tested. I emphasize the shortcomings of the very popular Resistive Force Theory (RFT) and indicate how the more rigorous Slender Body Theory (SBT) is able to overcome the limitations. In addition the chemotaxis of the marine bacterial strain Vibrio alginolyticus is studied with the revelation of a previously unknown chemotactic mechanism. Direct observations showed that these cells are able to bend their flagella to impart direction changes, which is paramount for an effective search strategy. This interesting find opens several intriguing questions pertaining to chemotaxis