Archaea-An International Microbiological Journal最新文献

The majority of cells in nature probably exist in a stationary-phase-like state, due to nutrient limitation in most environments. Studies on bacteria and yeast reveal morphological and physiological changes throughout the stationary phase, which lead to an increased ability to survive prolonged nutrient limitation. However, there is little information on archaeal stationary phase responses. We investigated protein- and lipid-level changes in Thermococcus kodakarensis with extended time in the stationary phase. Adaptations to time in stationary phase included increased proportion of membrane lipids with a tetraether backbone, synthesis of proteins that ensure translational fidelity, specific regulation of ABC transporters (upregulation of some, downregulation of others), and upregulation of proteins involved in coenzyme production. Given that the biological mechanism of tetraether synthesis is unknown, we also considered whether any of the protein-level changes in T. kodakarensis might shed light on the production of tetraether lipids across the same period. A putative carbon-nitrogen hydrolase, a TldE (a protease in Escherichia coli) homologue, and a membrane bound hydrogenase complex subunit were candidates for possible involvement in tetraether-related reactions, while upregulation of adenosylcobalamin synthesis proteins might lend support to a possible radical mechanism as a trigger for tetraether synthesis.

Host factors are regarded as important in shaping the archaeal community in the rumen but few controlled studies have been performed to demonstrate this across host species under the same environmental conditions. A study was designed to investigate the structure of the methanogen community in the rumen of two indigenous (yak and Tibetan sheep) and two introduced domestic ruminant (cattle and crossbred sheep) species raised and fed under similar conditions on the high altitude Tibetan Plateau. The methylotrophic Methanomassiliicoccaceae was the predominant archaeal group in all animals even though Methanobrevibacter are usually present in greater abundance in ruminants globally. Furthermore, within the Methanomassiliicoccaceae family members from Mmc. group 10 and Mmc. group 4 were dominant in Tibetan Plateau ruminants compared to Mmc. group 12 found to be highest in other ruminants studied. Small ruminants presented the highest number of sequences that belonged to Methanomassiliicoccaceae compared to the larger ruminants. Although the methanogen community structure was different among the ruminant species, there were striking similarities between the animals in this environment. This indicates that factors such as the extreme environmental conditions and diet on the Tibetan Plateau might have a greater impact on rumen methanogen community compared to host differences.

The Lon protease is highly evolutionarily conserved. However, little is known about Lon in the context of gut microbial communities. A gene encoding a Lon-like protease (Lon-like-Ms) was identified and characterized from Methanobrevibacter smithii, the predominant archaeon in the human gut ecosystem. Phylogenetic and sequence analyses showed that Lon-like-Ms and its homologs are newly identified members of the Lon family. A recombinant form of the enzyme was purified by affinity chromatography, and its catalytic properties were examined. Recombinant Lon-like-Ms exhibited ATPase activity and cleavage activity toward fluorogenic peptides and casein. The peptidase activity of Lon-like-Ms relied strictly on Mg(2+) (or other divalent cations) and ATP. These results highlight a new type of Lon-like protease that differs from its bacterial counterpart.

Inorganic storage granules have long been recognized in bacterial and eukaryotic cells but were only recently identified in archaeal cells. Here, we report the cellular organization and chemical compositions of storage granules in the Euryarchaeon, Archaeoglobus fulgidus strain VC16, a hyperthermophilic, anaerobic, and sulfate-reducing microorganism. Dense granules were apparent in A. fulgidus cells imaged by cryo electron microscopy (cryoEM) but not so by negative stain electron microscopy. Cryo electron tomography (cryoET) revealed that each cell contains one to several dense granules located near the cell membrane. Energy dispersive X-ray (EDX) spectroscopy and scanning transmission electron microscopy (STEM) show that, surprisingly, each cell contains not just one but often two types of granules with different elemental compositions. One type, named iron sulfide body (ISB), is composed mainly of the elements iron and sulfur plus copper; and the other one, called polyphosphate body (PPB), is composed of phosphorus and oxygen plus magnesium, calcium, and aluminum. PPBs are likely used for energy storage and/or metal sequestration/detoxification. ISBs could result from the reduction of sulfate to sulfide via anaerobic energy harvesting pathways and may be associated with energy and/or metal storage or detoxification. The exceptional ability of these archaeal cells to sequester different elements may have novel bioengineering applications.