Coloured scanning electron micrograph of Leptothrix sp. filamentous iron-oxidizing bacteria. Leptothrix is a chemolithotrophic prokaryote that forms dense rope-like threads that grow in fresh water on the surface of submerged rocks. Often the ends of the filaments are seen protruding from the rope-like threads. The delicate threads are golden brown in colour. Magnification: x400 when shortest axis printed at 25 millimetres.