Local versus global diversity of microorganisms: cryptic diversity of ciliated protozoa

Microbial species diversity both global and local, is still poorly understood. III this study all species of ciliated protozoa were recorded microscopically from similar to 1 cm(2) sediment collected from a small lake and item a marine shallow-water bay. Additional adjacent sediment samples (together representing < 50 cm(2)) were then incubated under a variety of culture conditions to reveal ''cryptic species'' that are present as resting cysts or are too rare to be found microscopically. About 85 and 57% of the total number of observed species from the limnic and marine sediment, respectively, were such cryptic species. In both cases the number of species found in < 50 cm(2) of sediment represented about 75% of all ciliate species ever recorded from these two previously well-studied habitats, and about 8% of all named free-living ciliates. These observations support the assumption thar in the case of microorganisms ''everything is everywhere'' and that their global species diversity is relatively limited.