Global Diversity of Desert Hypolithic Cyanobacteria.

Global patterns in diversity were estimated for cyanobacteria-dominated hypolithic communities that colonize ventral surfaces of quartz stones and are common in desert environments. A total of 64 hypolithic communities were recovered from deserts on every continent plus a tropical moisture sufficient location. Community diversity was estimated using a combined t-RFLP fingerprinting and high throughput sequencing approach. The t-RFLP analysis revealed desert communities were different from the single non-desert location. A striking pattern also emerged where Antarctic desert communities were clearly distinct from all other deserts. Some overlap in community similarity occurred for hot, cold and tundra deserts. A further observation was that the producer-consumer ratio displayed a significant negative correlation with growing season, such that shorter growing seasons supported communities with greater abundance of producers, and this pattern was independent of macroclimate. High-throughput sequencing of 16S rRNA and nifH genes from four representative samples validated the t-RFLP study and revealed patterns of taxonomic and putative diazotrophic diversity for desert communities from the Taklimakan Desert, Tibetan Plateau, Canadian Arctic and Antarctic. All communities were dominated by cyanobacteria and among these 21 taxa were potentially endemic to any given desert location. Some others occurred in all but the most extreme hot and polar deserts suggesting they were relatively less well adapted to environmental stress. The t-RFLP and sequencing data revealed the two most abundant cyanobacterial taxa were Phormidium in Antarctic and Tibetan deserts and Chroococcidiopsis in hot and cold deserts. The Arctic tundra displayed a more heterogenous cyanobacterial assemblage and this was attributed to the maritime-influenced sampling location. The most abundant heterotrophic taxa were ubiquitous among samples and belonged to the Acidobacteria, Actinobacteria, Bacteroidetes, and Proteobacteria. Sequencing using nitrogenase gene-specific primers revealed all putative diazotrophs were Proteobacteria of the orders Burkholderiales, Rhizobiales, and Rhodospirillales. We envisage cyanobacterial carbon input to the system is accompanied by nitrogen fixation largely from non-cyanobacterial taxa. Overall the results indicate desert hypoliths worldwide are dominated by cyanobacteria and that growing season is a useful predictor of their abundance. Differences in cyanobacterial taxa encountered may reflect their adaptation to different moisture availability regimes in polar and non-polar deserts.

Eukarya associated with the stony coral Oculina patagonica from the Mediterranean Sea.

Oculina patagonica is a putative alien scleractinian coral from the Southwest Atlantic that inhabits across the Mediterranean Sea. Here, we have addressed the diversity of Eukarya associated with this coral and its changes related to the environmental conditions and coral status. A total of 46 colonies of O. patagonica were taken from Alicante coast (Spain) and Pietra Ligure coast (Italy) and analyzed using denaturing gradient gel electrophoresis (DGGE) of the small-subunit 18S rRNA and 16S plastid rRNA genes, internal transcribed spacer region 2 (ITS 2) analyses, and electron microscopy. Our results show that Eukarya and plastid community associated to O. patagonica change with environmental conditions and coral status. Cryptic species, which can be difficult to identify by optical methods, were distinguished by 18S rRNA gene DGGE: the barnacle Megatrema anglicum, which was detected at two locations, and two boring sponges related to Cliona sp. and Siphonodictyon coralliphagum detected in samples from Tabarca and Alicante Harbour, respectively. Eukaryotic phototrophic community from the skeletal matrix of healthy corals was dominated by Ochrosphaera sp. while bleached corals from the Harbour and Tabarca were associated to different uncultured phototrophic organism. Differences in ultrastructural morphologies of the zooxanthellae between healthy and bleached corals were observed. Nevertheless, no differences were found in Symbiodinium community among time, environments, coral status and location, showing that O. patagonica hosted only one genotype of Symbiodinium belonging to clade B2. The fact that this clade has not been previously detected in other Mediterranean corals and is more frequent in the tropical Western Atlantic, is a new evidence that O. patagonica is an alien species in the Mediterranean Sea.

Characterization of chasmoendolithic community in Miers Valley, McMurdo Dry Valleys, Antarctica.

The Antarctic Dry Valleys are unable to support higher plant and animal life and so microbial communities dominate biotic ecosystem processes. Soil communities are well characterized, but rocky surfaces have also emerged as a significant microbial habitat. Here, we identify extensive colonization of weathered granite on a landscape scale by chasmoendolithic microbial communities. A transect across north-facing and south-facing slopes plus valley floor moraines revealed 30-100 % of available substrate was colonized up to an altitude of 800 m. Communities were assessed at a multidomain level and were clearly distinct from those in surrounding soils and other rock-inhabiting cryptoendolithic and hypolithic communities. All colonized rocks were dominated by the cyanobacterial genus Leptolyngbya (Oscillatoriales), with heterotrophic bacteria, archaea, algae, and fungi also identified. Striking patterns in community distribution were evident with regard to microclimate as determined by aspect. Notably, a shift in cyanobacterial assemblages from Chroococcidiopsis-like phylotypes (Pleurocapsales) on colder-drier slopes, to Synechococcus-like phylotypes (Chroococcales) on warmer-wetter slopes. Greater relative abundance of known desiccation-tolerant bacterial taxa occurred on colder-drier slopes. Archaeal phylotypes indicated halotolerant taxa and also taxa possibly derived from nearby volcanic sources. Among the eukaryotes, the lichen photobiont Trebouxia (Chlorophyta) was ubiquitous, but known lichen-forming fungi were not recovered. Instead, fungal assemblages were dominated by ascomycetous yeasts. We conclude that chasmoendoliths likely constitute a significant geobiological phenomenon at lower elevations in granite-dominated Antarctic Dry Valley systems.