1 Introduction and Background

The rod-like, contractile stalk of the single-celled peritrich Vorticella Convalleria can collapse into a tightly coiled helix in less than 1/60 second, a rate ~1000 times its cell body size per second. The contractile stalk (25um-300um in length, ~ 4um diameter) consists of several membranes stiffened by extracellular fibers and helical assembly of larger protein bundles, known as batonets, surrounding an asymmetrically located protein bundle of roughly parallel filaments known as the spasmoneme. The contraction mechanism is thought to be the entropic collapse of spasmin, the negatively charged polyelectrolytic protein that composes the spasmoneme, via Ca screening of electrostatic repulsion. The structure and chemical composition of the stalk and spasmoneme are largely unknown. After culturing Vorticella Convalleria, samples were prepared by filtering detached cells. The resulting high cell content aqueous solution was then placed on freshly cleaved mica substrates and allowed to dry for ~30min, until all water had evaporated. The samples were then imaged via contact mode atomic force microscopy (AFM). The structure of stalk was revealed in great detail. The following was clearly visualized; the helicity of the stalk, the spasmonene (3um diameter), batonets (180nm), the outer stalk sheath membrane morphology and folds in the sheath membrane, and organells in the stalk. We were also able to image a circular stalk "foot" (2.8 um diameter) where the organism attached itself to the substrate, as well as what appears to be the biological "glue" used for surface attachment. Thesis Supervisor: Christine Ortiz Title: Assistant Professor of Materials Science and Engineering