Natural communities of novel archaea and bacteria with a string-of-pearls-like morphology: molecular analysis of the bacterial partners.

A recently discovered bacterial/archaeal association, growing in a string-of-pearls-like structure, thrives in the cold (approximately 10 degrees C) sulfidic marsh water of the Sippenauer Moor near Regensburg, Bavaria, Germany. It forms characteristic, macroscopically visible globules, the pearls, containing microcolonies of novel euryarchaeota, which are surrounded by mainly filamentous bacteria (C. Rudolph, G. Wanner, and R. Huber, Appl. Environ. Microbiol. 67:2336-2344, 2001). Single pearls in series are connected by white threads. Here we report the first detailed molecular investigations of the taxonomic affiliation of the bacteria contributing to the strings of pearls. Phylogenetic analysis showed the dominance of a single phylotype (clone sipK4) within single pearls most closely related to Thiothrix unzii. The presence of Thiothrix sipK4 as a major constituent of single pearls and of the pearl-connecting white threads was verified by fluorescence in situ hybridization.