Bacterial actuation and manipulation are demonstrated where Magnetospirillum gryphiswaldense magnetotactic bacteria ͑MTB͒ are used to push 3 m beads at an average velocity of 7.5 m s −1 along preplanned paths by modifying the torque on a chain of magnetosomes in the bacterium with a directional magnetic field of at least 0.5 G generated from a small programmed electrical current. But measured average thrusts of 0.5 and 4 pN of the flagellar motor of a single Magnetospirillum gryphiswaldense and MC-1 MTB suggest that average velocities greater than 16 and 128 m s −1 , respectively could be achieved.The behaviors of bacteria in low Reynolds number hydrodynamics 1 suggest that they could be used to manipulate efficiently suspended micro-objects in fluids for potential applications in microsystems such as lab-on-a-chip and Micro-Total-Analysis Systems. Here, electro-osmosis 2 or dielectrophoresis 3 based on the principle of electrokinetics is used where frequencies and voltage amplitudes dependent on dielectric properties are required to induce a force. Our method referred here to as bacterial manipulation is independent of the dielectric properties and may prove to be suitable for many applications when low electrical power and compactness are required.The integration of bacteria as functional components has been previously done, 4,5 where Serratia marcescens flagellated bacteria were attached to polydimethylsiloxane or polystyrene to form a bacterial carpet for moving fluid. Until then, bacteria were operating without external control appropriate for manipulation of micro-objects. Typical bacteria swims according to the so-called run-and-tumble pattern that can be explained by chemotaxis 6 models while remaining unpredictable for micromanipulation. We show here that magnetotactic bacteria ͑MTB͒ are more appropriate to carry out computer-based controlled micromanipulation or microactuation of micro-objects.The exploitation of the motility of MTB has been done in the past such as in low field orientation magnetic separation 7 being a process, where motile, magnetic field susceptible MTB can be separated. Micromanipulation of MTB using microelectromagnets arrays has also been described. 8,9 In all these previous examples, MTB were the entities being manipulated instead of being used to manipulate other objects as described here.Each MTB ͑Ref. 10͒ possesses a chain of magnetosomes which are membrane-based nanoparticles of a magnetic iron. Because of this chain, the swimming direction of MTB although influenced by chemotaxis and aerotaxis is mainly based on magnetotaxis, 11-13 being more "compatible" with electronics and computer-based software platforms. Al-though several types of MTB exist and can be found all over the world, in this study, Magnetospirillum gryphiswaldense bacteria 14 were used. This MTB has a length of ϳ1-3 m with a swimming speed of ϳ40-80 m / s. Magnetotaxis as chemotaxis 15-17 also influences the motility of MTB in search of nutrient gradients. To modify the paths of the MTB, magnetic field lines ...