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Moving Fluid with Bacterial Carpets

Nicholas Darnton ^*, Linda Turner ^*, Kenneth Breuer  and Howard C. Berg ^*

^* Rowland Institute at Harvard, Cambridge, Massachusetts 02142; and Division of Engineering, Brown University, Providence, Rhode Island 02192

Correspondence: Address reprint requests to Howard C. Berg, E-mail: hberg{at}biosun.harvard.edu.

We activated a solid-fluid interface by attaching flagellated bacteria to a solid surface. We adsorbed swarmer cells of Serratia marcescens to polydimethylsiloxane or polystyrene. The cell bodies formed a densely packed monolayer while their flagella continued to rotate freely. Motion of the fluid close to an extended flat surface, visualized with tracer beads, was dramatically enhanced compared to the motion farther away. The tracer beads revealed complex ever-changing flow patterns, some linear (rivers), others rotational (whirlpools). Typical features of this flow were small (tens of µm) and reasonably stable (many minutes). The surface performed active mixing equivalent to diffusion with a coefficient of 2 x 10^-7 cm²/s. We call these flat constructs "bacterial carpets". When attached to polystyrene beads or to fragments of polydimethylsiloxane, the bacteria generated both translation and rotation. We call these constructs "auto-mobile beads" or "auto-mobile chips". Given the size and strength of the flow patterns near the carpets, the motion must be generated by small numbers of coordinated flagella. We should be able to produce larger and longer-range effects by increasing coordination.

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