The topography of soft, adhesive diatom 'trails' as observed by atomic force microscopy

Gliding diatoms foul surfaces by leaving behind 'trails' of secreted mucilage. Atomic force microscopy (AFM) used in 'fluid tapping' mode enabled the topography of the soft, adhesive trails in the natural hydrated state to be imaged, and without the artefacts resulting from fixation and/or dehydration. Diatom trails consist of a continuous, swollen ridge of material that dominates the trail, as well as a diffuse hydrated mucilage coating observed on either side of the main trail. The main trail material is evenly attached to the coverslip along its entire length, and appears to cure, or become less soft/adhesive, over time. Diatom trails observed with the scanning electron microscope were severely damaged by dehydration, while trails imaged by the AFM in 'contact' mode were damaged and/or removed by the action of the cantilever. The AFM used in 'fluid tapping' mode is an excellent tool for topographical studies of soft/adhesive biological molecules in the hydrated state, and will have great value for measuring their physical and mechanical properties when operated in 'force modulation' mode.