RESUMEN
There are two groups of microorganisms that live and grow in hypersaline (>10-15% NaCl) environments: the halophilic Archaea and the halotolerant Bacteria and algae. In order to grow and reproduce in such high-salt, low-water activity environments, these organisms have made basic biochemical adaptations in their proteins, osmoregulation mechanisms, nucleic acids, and lipids. The environment of the halophiles and especially how the halophilic Archaea have adapted to that environment are reviewed in this paper. Along with this review is a brief description of how these adaptations could be important in the detection of life on early Mars assuming similar types of salts and a carbon-based life.
Asunto(s)
Adaptación Biológica , Halobacteriales/metabolismo , Marte , Cloruro de Sodio/química , Adaptación Fisiológica , Proteínas Arqueales/metabolismo , Proteínas Bacterianas/metabolismo , Microbiología Ambiental , Exobiología , Halobacteriales/efectos de la radiación , Concentración de Iones de Hidrógeno , Iones , Luz , Metabolismo de los Lípidos , Ácidos Nucleicos/metabolismo , Presión Osmótica , Oxígeno/metabolismo , Agua de Mar/química , TemperaturaRESUMEN
Extremely halophilic archaebacteria have been reported to have no capacity for dark repair (excision repair) of ultraviolet damage and to rely on very efficient photoreactivation for recovery after UVC irradiation. Post-UV incubation in the light restores 100% survival in these organisms. This has been taken to indicate that cyclobutane dimers are the only significant UV-induced lesions and that they are completely repaired by photoreactivation. However, in all organisms studied to date, pyrimidine (6-4) pyrimidone photoproducts are a significant cytotoxic and mutagenic lesion and constitute 10-30% of UV photoproducts. The question arises, therefore--are 6-4 photoproducts induced in the halophilic archaebacteria and, if they are, how are they repaired? This paper shows that both cyclobutane dimers and 6-4 photoproducts are induced in the extremely halophilic archaebacteria, Halobacterium cutirubrum, Halobacterium halobium and Haloferax volcanii, at similar levels as in other organisms. Furthermore, contrary to previous reports, there is dark repair of both lesions. As in other organisms, 6-4 photoproducts are removed more efficiently than cyclobutane dimers in the dark. In the light, cyclobutane dimers are repaired very rapidly and there is also photoenhanced repair of 6-4 photoproducts. This work confirms that organisms such as Halobacterium and Haloferax which live in conditions of high exposure to sunlight have very efficient rates of repair of UV lesions in the light.
Asunto(s)
Daño del ADN , Reparación del ADN , ADN Bacteriano/efectos de la radiación , Halobacteriales/efectos de la radiación , Rayos Ultravioleta , ADN Bacteriano/genética , Oscuridad , Halobacteriales/genética , Halobacteriales/metabolismo , Halobacterium/genética , Halobacterium/metabolismo , Halobacterium/efectos de la radiación , Halobacterium salinarum/genética , Halobacterium salinarum/metabolismo , Halobacterium salinarum/efectos de la radiación , Cinética , Dímeros de Pirimidina/análisis , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/efectos de la radiación , Factores de TiempoRESUMEN
The reconstitution of pharaonis phoborhodopsin was performed by incubation of its opsin with 13-cis-retinal. Spectrum change was very slow, and two phases of the change were observed: the first and second phases are due to the transient formation of 13-cis pigment and spontaneous isomerization to all-trans-retinal, respectively. Slow binding supports an idea that the retinal binding pocket of ppR is highly restricted. Being bent in the configuration, 13-cis-retinal cannot be accommodated in the pocket due to the steric hindrance. This is a possible reason for the lack of light-dark adaptation.