Microbial ecology of Azorean hot springs revealed by culture and molecular techniques

Contrary to the general idea that bacteria are ubiquitous, there are many ecological zones where extremophilic microorganisms cannot thrive. Given this, adjacent hot springs with similar environmental conditions should harbor similar thermophilic microbial communities compared with geographically distant communities. Furthermore, because thermophilic microbial communities depend on chemolithautotrophic primary production, it is likely that inter- and intra-site diversity will rely more on in situ geochemistry than on physical environmental factors. Molecular and classical microbiological techniques were used to determine the microbial composition and metabolic properties of the Azorean hot-springs microbial ecosystem. Molecular analyses included a phylogenetic survey of small-subunit rRNA by fluorescent in situ hybridization, clone library analysis, denaturing gradient gel electrophoreses, and gene sequencing. Classical microbiological culture approaches included elective enrichment, isolation, and characterization of isolated strains. This study was conducted at five terrestrial hot springs and two shallow marine areas on S. Miguel Island, Azores, over a period of four years. Environmental factors, including temperature, pH, nutrients, dissolved oxygen, precipitation, and salinity were measured. Only in situ temperature and monthly precipitation showed significant correlations with microbial diversity. Water temperature influence on diversity became more prominent during winter. The Azorean hot springs harbor communities with high turnover, reflected by a higher within-date similarity than within-site similarity. Patterns of community structure, for sites with similar environmental conditions, were partially explained (≥ 60%) by geographical distance, indicating that other ecological factors must also contribute to this pattern. Sao Miguel's near neutral terrestrial hot springs were dominated by chemolithautotrophic organisms from the Bacteria domain, order Aquificales. Sulfurihydrogenibium azorense, a new Aquificales species, was isolated and characterized from the Azores and is closely related to environmental sequences found in hot springs in Iceland (99.8%) and Yellowstone National Park (97%). In addition to S. azorense, 15 new isolates were also isolated. This study has improved the understanding of the ecology of the Azorean thermal systems, and supplied physiological and biogeographical characterization of the major microbial components of the near neutral hot springs environment inhabitants, the Aquificales.