The archaellum is the macromolecular machinery that Archaea use for propulsion or surface adhesion, enabling them to proliferate and invade new territories. The molecular composition of the archaellum and of the motor that drives it appears to be entirely distinct from that of the functionally equivalent bacterial flagellum and flagellar motor. Yet, the structure of the archaellum machinery is scarcely known. Using combined modes of electron cryo-microscopy (cryoEM), we have solved the structure of the Pyrococcus furiosus archaellum filament at 4.2 Å resolution and visualise the architecture and organisation of its motor complex in situ. This allows us to build a structural model combining the archaellum and its motor complex, paving the way to a molecular understanding of archaeal swimming motion.DOI: http://dx.doi.org/10.7554/eLife.27470.001

A novel chemolithoautotrophic, hyperthermophilic methanogen was isolated from a submarine hydrothermal system at the Kolbeinsey Ridge, north of Iceland. Based on its 16S rRNA gene sequence, the strain belongs to the order Methanococcales within the genus Methanocaldococcus, with approximately 95 % sequence similarity to Methanocaldococcus jannaschii as its closest relative. Cells of the novel organism stained Gram-negative and appeared as regular to irregular cocci possessing more than 50 polar flagella. These cell appendages mediated not only motility but also adherence to abiotic surfaces and the formation of cell-cell contacts. The new isolate grew at 55-90 6C, with optimum growth at 80 6C. The optimum NaCl concentration for growth was 2.5 % (w/v), and the optimal pH was 6.5. The cells gained their energy exclusively by reduction of CO 2 with H 2 . Selenate, tungstate and yeast extract stimulated growth significantly. The genome size was determined to be in the range 1.8-2.0 kb, and the G+C content of the genomic DNA was 30 mol%. Despite being physiologically nearly identical to the other members of the genus Methanocaldococcus, analysis of whole-cell proteins revealed significant differences. Based on the results from phylogenetic, morphological and protein analyses, we conclude that the novel strain represents a novel species of the genus Methanocaldococcus, for which the name Methanocaldococcus villosus sp. nov. is proposed (type strain KIN24-T80 T 5DSM 22612 T 5JCM 16315 T ).At the time of writing, the order Methanococcales consists of two families, the mesophilic and slightly thermophilic Methanococcaceae and the hyperthermophilic Methanocaldococcaceae. The latter contains the genera Methanocaldococcus and Methanotorris, separated by more than 7 %

Power-to-Methane as one part of Power-to-Gas has been recognized globally as one of the key elements for the transition towards a sustainable energy system. While plants that produce methane catalytically have been in operation for a long time, biological methanation has just reached industrial pilot scale and near-term commercial application. The growing importance of the biological method is reflected by an increasing number of scientific articles describing novel approaches to improve this technology. However, these studies are difficult to compare because they lack a coherent nomenclature. In this article, we present a comprehensive set of parameters allowing the characterization and comparison of various biological methanation processes. To identify relevant parameters needed for a proper description of this technology, we summarized existing literature and defined system boundaries for Power-to-Methane process steps. On this basis, we derive system parameters providing information on the methanation system, its performance, the biology and cost aspects. As a result, three different standards are provided as a blueprint matrix for use in academia and industry applicable to both, biological and catalytic methanation. Hence, this review attempts to set the standards for a comprehensive description of biological and chemical methanation processes.

Archaea use a molecular machine, called the archaellum, to swim. The archaellum consists of an ATP-powered intracellular motor that drives the rotation of an extracellular filament composed of multiple copies of proteins named archaellins. In many species, several archaellin homologs are encoded in the same operon; however, previous structural studies indicated that archaellum filaments mainly consist of only one protein species. Here, we use electron cryo-microscopy to elucidate the structure of the archaellum from Methanocaldococcus villosus at 3.08 Å resolution. The filament is composed of two alternating archaellins, suggesting that the architecture and assembly of archaella is more complex than previously thought. Moreover, we identify structural elements that may contribute to the filament’s flexibility.

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