Local versus Global Diversity of Microorganisms: Cryptic Diversity of Ciliated Protozoa

Microbial species diversity. both global and local, is still poorly understood. In this study all species of ciliated protozoa were recorded microscopically from ∼1 cm 2 sediment collected from a small lake and from a marine shallow-water bay. Additional adjacent sediment samples (together representing <50 cm 2 ) 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 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 that in the case of microorganisms everything is everywhere and that their global species diversity is relatively limited.