要　旨：Chile is topographically and climatically diverse. A wide array of diverse undisturbed extreme environments are represented in the country, such that native plants are highly adapted to local conditions. We have explored the i) bacterial community structures, ii) bacterial alkaline phosphomonoesterases (APases), and iii) putative plant growth-promoting (PGP) bacteria in the rhizosphere of plants grown in representative Chilean extreme environments (Atacama Desert, Andes Mountain, Patagonia and Antarctica). Molecular approaches (DGGE, 454-pyrosequencing and qPCR) revealed the presence of Proteobacteria, Bacteroidetes, and Actinobacteria as the dominant phyla in the rhizosphere soils of native plants. The results also showed the occurrence of bacterial APase genes (phoD and phoX) in all studied soils. Differences in total and APase-harboring bacterial populations between extreme environments and between plant species were also observed. In general, the significant lowest bacterial diversities, APase gene abundances, and APase activities were observed in soils from Atacama Desert. The APase gene abundances were positively correlated among them and with APase activity of soils, but negatively correlated with phosphorus (P) availability in rhizosphere soils. Finally, some culture isolates showed PGP traits (organic P hydrolyzing, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity and production of auxin) and their inoculation stimulated the growth of wheat plantlets under differing growth conditions, soil type and water shortage. Further studies are needed to determine which environmental factors regulate the structures of rhizobacterial communities, and how (or if) specific bacterial groups may contribute to the growth and survival of native plants in each extreme environment. Our studies also evidence possible applications of bacteria from extreme environments to improve wheat growth in soils under water shortage conditions by adverse climate events.

要　旨：Rhizobia have been used for a long time to improve plant growth and information on medicinal use of legumes was recorded by Hippocrates in 4th century B.C. the Romans knew of the benefits of soil movement to improve crops. Rhizobia were first isolated in the 1800’s and the Nitragin Company was founded in 1898 after a Milwaukee entrepreneur purchased rights to a commercial process for the production of nitrogen-fixing rhizobia. Despite the use of rhizobial inoculants for more than 200 years, we know very little about their ecosphysiology in natural soils. This broad genetic and physiological diversity of the rhizobia makes generalization difficult and does not allow for a “Unified General Theory” concerning their ecology. Moreover, our lack of understanding is due to the heterogeneity of rhizobia and soils, changing environmental conditions, and false assumptions from lab studies. It has always been assumed that the competitiveness of strains infecting legumes is dependent upon environmental conditions, and presuming that they are indigenous, they are likely more fit to interact with host plants than more recent bacterial additions to soils. However, there is no easy definition of indigenous and bacterial survival is influenced by a variety of stress factors. To address these questions, we started out by looking at what it means to be indigenous. Here we report the on the extra long-term saprophytic survival of rhizobia and show that we still know little about being indigenous.

要　旨： Microalgae, i.e. oxygen-evolving photosynthetic protists, are ubiquitous in aquatic environments. Together with cyanobacteria, these microorganisms respond for most of the primary production in the oceans. In coastal waters, microalgae form massive blooms that can be harmful both to humans and to marine life. Contamination of shellfish with phycotoxins that rend them unsafe for human consumption and massive fish kills are among the unwanted, direct effects of algal blooms in coastal areas. Human-driven changes in marine ecosystems, especially eutrophication and climate-induced changes that result in increased temperature and alterations in precipitation patterns are increasing the frequency and intensity of algal blooms in coastal environments worldwide. Moreover, a shift in microalgae community composition from autotrophic towards mixotrophic species, mainly flagellated forms, is expected to occur in this changing environment. Blooming microalgae interact in many ways with other components of the aquatic microbiota. During massive blooms, exudates from microalgal cells fuel bacterial secondary production. The rich microenvironment created during algal blooms is known to promote the growth of pathogenic bacteria such as vibrios. Associations of bacteria with algal cells can provide refuge from predation, conferring these bacteria competitive advantage to proliferate during algal blooms. On the other hand, several bacteria have been shown to elicit pathogenic effects against marine microalgae, acting as an important loss factor for algal populations and a potential mechanism of bloom control. Likewise, microalgae can display allelopathic effects on bacteria. Such diversity of interactions among microalgae and bacteria can be species-specific and are influenced by environmental factors. Thus, detailed studies are needed to elucidate algal bloom dynamics and their associate microbial communities for particular marine environments.