Project description:Methylmercury (MeHg), a neurotoxic substance that accumulates in aquatic food chains and poses a risk to human health, is synthesized by anaerobic microorganisms in the environment. To date, mercury (Hg) methylation has been attributed to sulfate- and iron-reducing bacteria (SRB and IRB, respectively). Here we report that a methanogen, Methanospirillum hungatei JF-1, methylated Hg in a sulfide-free medium at comparable rates, but with higher yields, than those observed for some SRB and IRB. Phylogenetic analyses showed that the concatenated orthologs of the Hg methylation proteins HgcA and HgcB from M. hungatei are closely related to those from known SRB and IRB methylators and that they cluster together with proteins from eight other methanogens, suggesting that these methanogens may also methylate Hg. Because all nine methanogens with HgcA and HgcB orthologs belong to the class Methanomicrobia, constituting the late-evolving methanogenic lineage, methanogenic Hg methylation could not be considered an ancient metabolic trait. Our results identify methanogens as a new guild of Hg-methylating microbes with a potentially important role in mineral-poor (sulfate- and iron-limited) anoxic freshwater environments.
Project description:Microbially produced electrically conductive protein filaments are of interest because they can function as conduits for long-range biological electron transfer. They also show promise as sustainably produced electronic materials. Until now, microbially produced conductive protein filaments have been reported only for bacteria. We report here that the archaellum of Methanospirillum hungatei is electrically conductive. This is the first demonstration that electrically conductive protein filaments have evolved in Archaea Furthermore, the structure of the M. hungatei archaellum was previously determined (N. Poweleit, P. Ge, H. N. Nguyen, R. R. O. Loo, et al., Nat Microbiol 2:16222, 2016, https://doi.org/10.1038/nmicrobiol.2016.222). Thus, the archaellum of M. hungatei is the first microbially produced electrically conductive protein filament for which a structure is known. We analyzed the previously published structure and identified a core of tightly packed phenylalanines that is one likely route for electron conductance. The availability of the M. hungatei archaellum structure is expected to substantially advance mechanistic evaluation of long-range electron transport in microbially produced electrically conductive filaments and to aid in the design of "green" electronic materials that can be microbially produced with renewable feedstocks.IMPORTANCE Microbially produced electrically conductive protein filaments are a revolutionary, sustainably produced, electronic material with broad potential applications. The design of new protein nanowires based on the known M. hungatei archaellum structure could be a major advance over the current empirical design of synthetic protein nanowires from electrically conductive bacterial pili. An understanding of the diversity of outer-surface protein structures capable of electron transfer is important for developing models for microbial electrical communication with other cells and minerals in natural anaerobic environments. Extracellular electron exchange is also essential in engineered environments such as bioelectrochemical devices and anaerobic digesters converting wastes to methane. The finding that the archaellum of M. hungatei is electrically conductive suggests that some archaea might be able to make long-range electrical connections with their external environment.
Project description:Methanospirillum hungatei strain JF1 (DSM 864) is a methane-producing archaeon and is the type species of the genus Methanospirillum, which belongs to the family Methanospirillaceae within the order Methanomicrobiales. Its genome was selected for sequencing due to its ability to utilize hydrogen and carbon dioxide and/or formate as a sole source of energy. Ecologically, M. hungatei functions as the hydrogen- and/or formate-using partner with many species of syntrophic bacteria. Its morphology is distinct from other methanogens with the ability to form long chains of cells (up to 100 ?m in length), which are enclosed within a sheath-like structure, and terminal cells with polar flagella. The genome of M. hungatei strain JF1 is the first completely sequenced genome of the family Methanospirillaceae, and it has a circular genome of 3,544,738 bp containing 3,239 protein coding and 68 RNA genes. The large genome of M. hungatei JF1 suggests the presence of unrecognized biochemical/physiological properties that likely extend to the other Methanospirillaceae and include the ability to form the unusual sheath-like structure and to successfully interact with syntrophic bacteria.
Project description:We report the complete genome sequence of Methanospirillum hungatei strain GP1 (DSM 1101). Strain GP1 oxidizes H2, formate, and secondary alcohols as the substrates for methanogenesis. Members of the genus are model organisms used to study syntrophic growth with bacterial partners, but secondary alcohol metabolism remains poorly studied.
Project description:Archaea use flagella known as archaella-distinct both in protein composition and structure from bacterial flagella-to drive cell motility, but the structural basis of this function is unknown. Here, we report an atomic model of the archaella, based on the cryo electron microscopy (cryoEM) structure of the Methanospirillum hungatei archaellum at 3.4?Å resolution. Each archaellum contains ?61,500 archaellin subunits organized into a curved helix with a diameter of 10?nm and average length of 10,000?nm. The tadpole-shaped archaellin monomer has two domains, a ?-barrel domain and a long, mildly kinked ?-helix tail. Our structure reveals multiple post-translational modifications to the archaella, including six O-linked glycans and an unusual N-linked modification. The extensive interactions among neighbouring archaellins explain how the long but thin archaellum maintains the structural integrity required for motility-driving rotation. These extensive inter-subunit interactions and the absence of a central pore in the archaellum distinguish it from both the bacterial flagellum and type IV pili.