Viability of bacterial cells in optical tweezers

Optical trapping is an excellent tool for manipulation of microscopic objects. On one hand this manipulation capability opens the window towards novel ways of cellular studies. However the photodamage induced by high power lasers in live cells limits the usability of optical tweezers in biological experiments. The progress in the field of optical trapping brought in new and improved techniques, such as holographic tweezers, that extend the manipulation capabilities. These techniques may be used to minimize the harmful effects on live cells. We have studied E. coli bacteria in optical tweezers in order to compare various trapping configurations in terms cellular viability. We used the waggling motion of swimming cells to determine how long the cell stays alive in the trap. We used two trapping configurations: a) single trap arrangement where a cell orients along the optical axis of the trap, and b) a double trap arrangement where a cell is grabbed by two traps at the cell poles. In this latter configuration the cell body was less exposed to the laser light. Our results may help in designing experiments with live cells where extended timescales and minimal photodamage is necessary.