Ignicoccus hospitalis sp. nov., the host of ‘Nanoarchaeum equitans’

A novel chemolithoautotrophic and hyperthermophilic member of the genus Ignicoccus was isolated from a submarine hydrothermal system at the Kolbeinsey Ridge, to the north of Iceland. The new isolate showed high similarity to the two species described to date, Ignicoccus islandicus and Ignicoccus pacificus, in its physiological properties as well as in its unique cell architecture. However, phylogenetic analysis and investigations on the protein composition of the outer membrane demonstrated that the new isolate was clearly distinct from I. islandicus and I. pacificus. Furthermore, it is the only organism known so far which is able to serve as a host for ‘Nanoarchaeum equitans’, the only cultivated member of the ‘Nanoarchaeota’. Therefore, the new isolate represents a novel species of the genus Ignicoccus, which we name Ignicoccus hospitalis sp. nov. (type strain KIN4/IT=DSM 18386T=JCM 14125T).

Desulfurococcus fermentans sp. nov., a novel hyperthermophilic archaeon from a Kamchatka hot spring, and emended description of the genus Desulfurococcus

An obligately anaerobic, hyperthermophilic, organoheterotrophic archaeon, strain Z-1312T, was isolated from a freshwater hot spring of the Uzon caldera (Kamchatka Peninsula, Russia). The cells were regular cocci, 1–4 μm in diameter, with one long flagellum. The cell envelope was composed of a globular layer attached to the cytoplasmic membrane. The temperature range for growth was 63–89 °C, with an optimum between 80 and 82 °C. The pH range for growth at 80 °C was 4·8–6·8, with an optimum at pH 6·0. Strain Z-1312Tgrew by hydrolysis and/or fermentation of a wide range of polymeric and monomeric substrates, including agarose, amygdalin, arabinose, arbutin, casein hydrolysate, cellulose (filter paper, microcrystalline cellulose, carboxymethyl cellulose), dextran, dulcitol, fructose, lactose, laminarin, lichenan, maltose, pectin, peptone, ribose, starch and sucrose. No growth was detected on glucose, xylose, mannitol or sorbitol. Growth products when sucrose or starch were used as the substrate were acetate, H2and CO2. Elemental sulfur, thiosulfate and nitrate added as potential electron acceptors for anaerobic respiration did not stimulate growth when tested with starch as the substrate. H2at 100 % in the gas phase did not inhibit growth on starch or peptone. The G+C content of the DNA was 42·5 mol%. 16S rRNA gene sequence analysis placed the isolated strain Z-1312Tas a member of the genusDesulfurococcus, where it represented a novel species, for which the nameDesulfurococcus fermentanssp. nov. (type strain Z-1312T=DSM 16532T=VKM V-2316T) is proposed.

The ultrastructure of Ignicoccus: evidence for a novel outer membrane and for intracellular vesicle budding in an archaeon

A novel genus of hyperthermophilic, strictly chemolithotrophic archaea, Ignicoccus, has been described recently, with (so far) three isolates in pure culture. Cells were prepared for ultrastructural investigation by cultivation in cellulose capillaries and processing by high-pressure freezing, freeze-substitution and embedding in Epon. Cells prepared in accordance with this protocol consistently showed a novel cell envelope structure previously unknown among the Archaea: a cytoplasmic membrane; a periplasmic space with a variable width of 20 to 400 nm, containing membrane-bound vesicles; and an outer sheath, approximately 10 nm wide, resembling the outer membrane of gram-negative bacteria. This sheath contained three types of particles: numerous tightly, irregularly packed single particles, about 8 nm in diameter; pores with a diameter of 24 nm, surrounded by tiny particles, arranged in a ring with a diameter of 130 nm; and clusters of up to eight particles, each particle 12 nm in diameter. Freeze-etched cells exhibited a smooth surface, without a regular pattern, with frequent fracture planes through the outer sheath, indicating the presence of an outer membrane and the absence of an S-layer. The study illustrates the novel complex architecture of the cell envelope of Ignicoccus as well as the importance of elaborate preparation procedures for ultrastructural investigations.

Segmentation of two- and three-dimensional data from electron microscopy using eigenvector analysis

An automatic image segmentation method is used to improve processing and visualization of data obtained by electron microscopy. Exploiting affinity criteria between pixels, e.g., proximity and gray level similarity, in conjunction with an eigenvector analysis, the image is subdivided into areas which correspond to objects or meaningful regions. Extending a proposal by Shi and Malik (1997, Proceedings of the IEEE conference on Computer Vision and Pattern Recognition, pp. 731-737) the approach was adapted to the field of electron microscopy, especially to three-dimensional application as needed by electron tomography. Theory, implementation, parameter setting, and results obtained with a variety of data are presented and discussed. The method turns out to be a powerful tool for visualization with the potential for further improvement by developing and tuning new affinity.

ATP synthesis at 100 degrees C by an ATPase purified from the hyperthermophilic archaeon Pyrodictium abyssi

The chemolithoautotrophic archaeon Pyrodictium abyssi isolate TAG 11 lives close to 100 degrees C and gains energy by sulfur respiration, with hydrogen as electron donor. From the membranes of this hyperthermophile, an ATPase complex was isolated. The purified enzyme consists of six major polypeptides, the 67, 51, 41, 26 and 22 kDa subunits composing the AF(1) headpiece, and the 7 kDa proteolipid of the AF(0) component. The headpiece of the enzyme restored the formation of ATP during sulfur respiration in membrane vesicles from which it had been removed by low salt treatment. Characteristics of the reconstituted activity suggest that the same enzyme is responsible for ATP formation in untreated membranes. ATP formation was neither sensitive to ionophores and uncouplers, nor to dicyclohexyl carbodiimide, but depended on closed vesicles. Both ATPase activity (up to 2 micromol per min and mg protein) as well as ATP formation (up to 0.4 micromol per min and mg membrane protein) were highest at 100 degrees C. A P/e2 ratio of close to one can be estimated for sulfur respiration with hydrogen. In addition to ATP, autoradiographic detection revealed the formation of high quantities of (33)P(i)-labeled ADP and of another compound not identified so far.