Natural communities of novel archaea and bacteria growing in cold sulfurous springs with a string-of-pearls-like morphology

Abstract

We report the identification of novel archaea living in close association with bacteria in the cold (approximately 10 degrees C) sulfurous marsh water of the Sippenauer Moor near Regensburg, Bavaria, Germany. These microorganisms form a characteristic, macroscopically visible structure, morphologically comparable to a string of pearls. Tiny, whitish globules (the pearls; diameter, about 0.5 to 3.0 mm) are connected to each other by thin, white-colored threads. Fluorescent in situ hybridization (FISH) studies have revealed that the outer part of the pearls is mainly composed of bacteria, with a filamentous bacterium predominating. Internally, archaeal cocci are the predominant microorganisms, with up to 10(7) cells estimated to be present in a single pearl. The archaea appear to be embedded in a polymer of unknown chemical composition. According to FISH and 16S rRNA gene sequence analysis, the archaea are affiliated with the euryarchaeal kingdom. The new euryarchaeal sequence represents a deep phylogenetic branch within the 16S rRNA tree and does not show extensive similarity to any cultivated archaea or to 16S rRNA gene sequences from environmental samples.

FIG. 1

Topographic map of the location of the Sippenauer Moor in Bavaria, Germany. The topographic map was generated using the Online Map Creation program (Geomar, Kiel, Germany; http://www.aquarius.geomar.de).

FIG. 2

Photograph of archaeal and bacterial communities growing in a morphologically characteristic structure (the strings of pearls) in the sulfurous water of the Sippenauer Moor. Orange arrows point to single pearls.

FIG. 3

FISH of a part of a pearl. (A) Phase-contrast micrograph. (B) Epifluorescence micrograph. Dual hybridization was done with a rhodamine green-labeled archaeal probe (ARCH915) and a CY3-labeled bacterial probe (EUB338). The archaeal cocci stain green; the bacteria stain red.

FIG. 4

16S rRNA gene-based phylogenetic tree showing the position of the archaeal sequence clone (SM1) derived from a single pearl. The topology of the tree is based on the results of a maximum-parsimony analysis (ARB software package [34, 35]). Reference sequences were chosen to represent the broadest diversity of archaea. The scale bar shows a 10% estimated difference in nucleotide sequence positions.

FIG. 5

Scanning electron micrographs of a single pearl from the Sippenauer Moor. (A) Overview of the inner part of a pearl, showing large numbers of small cocci. (B) Detail of the inset in panel A. Single round cocci are embedded in a fibrous matrix.