Gliding motility of Peloploca spp., and their distribution in the sediment and water column of a eutrophic lake

Observations indicating gliding motility in the gas-vacuolate, filamentous organism Peloploca were made using microcapillary tubes. Tubes containing semi-solid agar, incubated in sediment cores gave good enrichments of Peloploca spp. The organisms, which had the form of helical bundles of filaments, were seen to corkscrew through the agar at up to 2–3 m s^-1.The vertical distribution of Peloploca spp. in the sediment and water column of a eutrophic lake was examined periodically during summer stratification. The organisms were confined to anoxic conditions in the sediment prior to stratification. With increasing anoxia in the hypolimnion, the population shifted upwards in the sediment, and towards the end of stratification, in the most reducing conditions, appeared in the lower hypolimnion. Anaerobically incubated sediment cores also showed the movement of the Peloploca population from sediment into the overlying water.It is suggested that the gliding motility and helical morphology of Peloploca bundles enable them to migrate through sediment in response to oxygen and Eh gradients, in addition to their use of gas vacuoles to adjust their position in the water column. The taxonomic implications of gliding motility in Peloploca spp. are discussed.