Optical Tweezers Cause Physiological Damage to Escherichia coli and Listeria Bacteria

Abstract

We investigated the degree of physiological damage to bacterial cells caused by optical trapping using a 1,064-nm laser. The physiological condition of the cells was determined by their ability to maintain a pH gradient across the cell wall; healthy cells are able to maintain a pH gradient over the cell wall, whereas compromised cells are less efficient, thus giving rise to a diminished pH gradient. The pH gradient was measured by fluorescence ratio imaging microscopy by incorporating a pH-sensitive fluorescent probe, green fluorescent protein or 5(6)-carboxyfluorescein diacetate succinimidyl ester, inside the bacterial cells. We used the gram-negative species Escherichia coli and three gram-positive species, Listeria monocytogenes, Listeria innocua, and Bacillus subtilis. All cells exhibited some degree of physiological damage, but optically trapped E. coli and L. innocua cells and a subpopulation of L. monocytogenes cells, all grown with shaking, showed only a small decrease in pH gradient across the cell wall when trapped by 6 mW of laser power for 60 min. However, another subpopulation of Listeria monocytogenes cells exhibited signs of physiological damage even while trapped at 6 mW, as did B. subtilis cells. Increasing the laser power to 18 mW caused the pH gradient of both Listeria and E. coli cells to decrease within minutes. Moreover, both species of Listeria exhibited morepronounced physiological damage when grown without shaking than was seen in cells grown with shaking, and the degree of damage is therefore also dependent on the growth conditions.

Force-controlled spatial manipulation of viable mammalian cells and micro-organisms by means of FluidFM technology

“…[2][3][4][5][6][7] Exploiting the trapping forces due to the radiation pressure through intense and collimated lasers 8,9 viruses, bacteria as well as cellular organelles could be displaced in a controlled way. However, optical tweezers might damage cells, [10][11][12] and are not appropriate for detaching adherent, spread cells from surfaces. The latter also holds for glass micropipettes, [13][14][15] the oldest instrument to manipulate single organisms.…”

3D visualization of convection patterns in lab-on-chip with open microfluidic outlet

“…It is well known that all common technologies have a strong impact both on the particles and on the surrounding medium, hence limiting the applicability of these techniques. As an example, optical (Neuman et al 1999;Leitz et al 2002;Rasmussen et al 2008) and electromagnetic (Seger-Sauli et al 2005) trapping increase the local temperature through light absorption or the Joule effect, making the trapping environment uncomfortable for cells. This is particularly problematic when the biological material is required to maintain its natural function, and hence needs to be in a condition as similar as possible to its biological environment (Yang et al 2008).…”

On-chip manipulation of single microparticles, cells, and organisms using surface acoustic waves

“…Optical tweezers have since been used to trap and manipulate many kinds of micro/ nano objects, including dielectric spheres, metal particles, cells, bacteria, DNA, viruses, and molecular motors (5)(6)(7). Although optical tweezers have demonstrated excellent precision and versatility for a number of functionalities, they have two potential shortcomings: First, they may cause physiological damage to cells and other biological objects from potential laser-induced heating, multiphoton absorption in biological materials, and the formation of singlet oxygen (8); and second, they rely on complex, potentially expensive optical setups that are difficult to maintain and miniaturize. Many alternative bioparticle-manipulation techniques (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) have since been developed to overcome these shortcomings, however, each technique has its own potential drawbacks.…”