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

Abstract

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.

FIG. 1.

Photograph of archaeal and bacterial communities growing in a unique, string-of-pearls-like morphology in the sulfurous water of the Sippenauer Moor. Arrows point to single pearls. Bar, 3 cm.

FIG. 2.

16S rRNA gene-based phylogenetic tree showing the position of the bacterial sequence clones derived from a pearl. The topology of the tree is based on results of a maximum-parsimony analysis (ARB software package) (19). Reference sequences were chosen to represent the broadest diversity of Bacteria (scale bar, 10% estimated difference in nucleotide sequence positions). The accession numbers of the sequences occur after the species names and clone designations.

FIG. 3.

Phase-contrast micrograph of the outer part of a pearl, showing filamentous, rosette-forming microorganisms with sulfur globules. Bar, 20 μm.

FIG. 4.

(A) FISH of a part of a pearl. An epifluorescence micrograph, dually hybridized with a rhodamine green-labeled archaeal probe (ARCH915) and a CY3-labeled Thiothrix-specific probe (TN1), is shown. The archaeal cocci stain green, and Thiothrix stains red. (B) DAPI stain of the same sample. Bar, 10 μm.