RESUMO
Extreme environments may support communities of microalgae living at the limits of their tolerance. It is usually assumed that these extreme environments are inhabited by extremophile species. However, global anthropogenic environmental changes are generating new extreme environments, such as mining-effluent pools of residual waters from uranium mining with high U levels, acidity and radioactivity in Salamanca (Spain). Certain microalgal species have rapidly adapted to these extreme waters (uranium mining in this area began in 1960). Experiments have demonstrated that physiological acclimatisation would be unable to achieve adaptation. In contrast, rapid genetic adaptation was observed in waters ostensibly lethal to microalgae by means of rare spontaneous mutations that occurred prior to the exposure to effluent waters from uranium mining. However, adaptation to the most extreme conditions was only possible after recombination through sexual mating because adaptation requires more than one mutation. Microalgae living in extreme environments could be the descendants of pre-selective mutants that confer significant adaptive value to extreme contamination. These "lucky mutants" could allow for the evolutionary rescue of populations faced with rapid environmental change.
Assuntos
Adaptação Fisiológica , Microalgas/efeitos dos fármacos , Mineração , Urânio/toxicidade , Águas Residuárias/toxicidade , Poluentes Químicos da Água/toxicidade , Adaptação Fisiológica/genética , Microalgas/genética , Microalgas/crescimento & desenvolvimento , Mutação , Espanha , TempoRESUMO
Low-molecular-weight RNA analysis was performed for the identification and classification of 20 Argentinian strains isolated from the root nodules of Prosopis alba. SDS-PAGE of total cellular proteins, determination of the DNA base composition, DNA-DNA reassociation experiments and physiological and biochemical tests were also carried out for these strains and the whole 16S rRNA gene was sequenced from one of the strains, strain LMG 19008T. Results of the genotypic and phenotypic characterization showed that the strains isolated in this study belong to a group that clustered in the genus Mesorhizobium. The results of DNA-DNA hybridizations showed that this group is a novel species of this genus. The name Mesorhizobium chacoense sp. nov. is proposed for this species. The type strain is LMG 19008T (= CECT 5336T).
Assuntos
Filogenia , Rhizobiaceae/classificação , Rosales/microbiologia , Antibacterianos/farmacologia , Argentina , Composição de Bases , Metabolismo dos Carboidratos , Primers do DNA , DNA Bacteriano/genética , DNA Ribossômico/genética , Testes de Sensibilidade Microbiana , Dados de Sequência Molecular , Hibridização de Ácido Nucleico , Raízes de Plantas/microbiologia , Plasmídeos , Reação em Cadeia da Polimerase , RNA Ribossômico 16S/genética , Rhizobiaceae/efeitos dos fármacos , Rhizobiaceae/genética , Rhizobiaceae/fisiologiaRESUMO
An optimized technique of polyacrylamide gel electrophoresis, Staircase Electrophoresis (SCE), was applied to determine the stable Low Molecular Weight RNA (LMW RNA) profiles of 25 Frankia strains from diverse geographic origins and host specificity groups as well as species from other actinomycete genera. Application of the technique permits the rapid identification of Frankia strains and their differentiation from other actinomycetes. The isolates used in this study were grouped in eight clusters, each comprising strains with identical LMW RNA profiles. Comparison of these results with others obtained from DNA sequences or DNA hybridization methods suggest a high degree of complexity in the genus Frankia. Application of SCE to profile LMW RNA should in the future facilitate biodiversity studies of Frankia and discrimination of new species.
