RESUMEN
Several families of plasmids and viruses (PVs) have now been described in hyperthermophilic archaea of the order Thermococcales. One family of plasmids replicates by the rolling circle mechanism, whereas most other PVs probably replicate by the θ mode. PVs from Thermococcales encode novel families of DNA replication proteins that have only detectable homologues in other archaeal PVs. PVs from different families share a common gene pool and co-evolve with their hosts. Most Thermococcales also produce virus-like membrane vesicles similar to eukaryotic microparticles (ectosomes). Some membrane vesicles of Thermococcus nautilus harbour the plasmid pTN1, suggesting that vesicles can be involved in plasmid transfer between species.
Asunto(s)
Virus de Archaea/genética , Plásmidos/genética , Thermococcales/genética , Thermococcales/virología , Vesículas Transportadoras/química , Evolución Biológica , Membrana Celular/química , Membrana Celular/ultraestructura , Replicación del ADN , ADN de Archaea/metabolismo , ADN de Archaea/ultraestructura , Humanos , Conformación de Ácido Nucleico , Plásmidos/metabolismo , Thermococcales/ultraestructura , Proteínas Virales/química , Proteínas Virales/genéticaRESUMEN
Cultures of hyperthermophilic archaea (order Thermococcales) have been analyzed by electron microscopy and epifluorescence staining for the presence of virus-like particles. We found that most strains of Thermococcus and Pyrococcus produce various types of spherical membrane vesicles and unusual filamentous structures. Cellular DNA can be strongly associated with vesicles and appears as fluorescent dots by epifluorescence microscopy, suggesting that some particles assumed to be viruses in ecological studies might instead be vesicles associated with extracellular DNA. DNA in vesicle preparations is remarkably resistant to DNase treatment and thermodenaturation, indicating that association with vesicles could be an important factor determining DNA stability in natural environments.
Asunto(s)
Vesículas Citoplasmáticas/química , ADN de Archaea/química , Thermococcales/química , Thermococcales/genética , Vesículas Citoplasmáticas/genética , Vesículas Citoplasmáticas/ultraestructura , Vesículas Citoplasmáticas/virología , ADN de Archaea/genética , Temperatura , Thermococcales/ultraestructura , Thermococcales/virologíaRESUMEN
Fourteen strains of hyperthermophilic organotrophic anaerobic marine Archaea were isolated from shallow water and deep-sea hot vents, and four of them were characterized. These isolates, eight previously published strains, and six type strains of species of the order Thermococcales were selected for the study of cell wall components by means of thin sectioning or freeze-etching electron microscopy. The cell envelopes of most isolates were shown to consist of regularly arrayed surface protein layers, either single or double, with hexagonal lattice (p6) symmetry, as the exclusive constituents outside the cytoplasmic membrane. The S-layers studied differed in center-to-center spacing and molecular mass of the constituent protein subunits. Polyclonal antisera raised against the cells of 10 species were found to be species-specific and allowed 12 new isolates from shallow water hot vents to be identified as representatives of the species Thermococcus litoralis, Thermococcus stetteri, Thermococcus chitonophagus, and Thermococcus pacificus. Of the 7 deep-sea isolates, only 1 was identified as a T. litoralis strain. Thus, hyperthermophilic marine organotrophic isolates obtained from deep-sea hot vents showed greater diversity with regard to their S-layer proteins than shallow water isolates.
