In situ growth of the novel SM1 euryarchaeon from a string-of-pearls-like microbial community in its cold biotope, its physical separation and insights into its structure and physiology

Abstract

Recently, a unique archaeal/bacterial community that grows in a macroscopically visible string-of-pearls-like structure in cold (~10 °C), sulfurous marsh water was discovered. Here, a new technique is described that allows the fast and reliable growth of these string-of-pearls-like microbial communities in larger quantities on polyethylene nets in nature. The microbial net population, estimated to consist of about 10,000 single pearls, can be harvested once a week and the archaeal cells selectively separated by density gradient centrifugation. As in native pearls, the archaeal cell fraction obtained consisted of a single type of coccoid cells only, 0.6 µm in diameter. This novel type of euryarchaea has been tentatively named SM1 euryarchaeon. Electron microscopy and immuno-fluorescence in situ hybridization (immuno-FISH) revealed that about 100 pili-like fibers, up to 3 µm in length, emanate radially from the surface of each cell. The SM1 euryarchaeal cells exhibited a viability of about 90%. The optimal conditions for viability were temperatures between −2 °C and 20 °C, pH 5–9, and low salt conditions; cell viability was independent of oxygen partial pressures. The cultures stained gram-positive, the cell wall was sensitive to SDS, EDTA and Proteinase K treatment. The cells did not exhibit the typical fluorescence for methanogens and did not contain coenzyme F₄₂₀. The G+C-content was 34.5 mol%.