The effects of temperature, pH and sulphide on the community structure of hyperthermophilic streamers in hot springs of northern Thailand.

Hyperthermophilic community diversity was assessed in hot-spring streamers along gradients of temperature, pH and sulphide in northern Thailand. A hierarchical sampling design was employed to obtain biomass for culture-independent estimates of 16S rRNA gene-defined prokaryotic diversity. All springs supported several archaeal and bacterial phylotypes, including novel phylotypes that expand the known phylogenetic diversity of terrestrial hyperthermophiles. Diversity appeared significantly greater than that observed for several other geographic locations. Phylotypes belonging to the Aquificales were ubiquitous, further supporting the hypothesis that these chemolithoautotrophs are key members of all hyperthermophilic communities. The chemoorganotrophic genus Thermus was also represented by phylotypes in all springs. Other bacterial taxa represented by environmental sequences included Bacillus, Thermotoga and various unidentified Alphaproteobacteria and Betaproteobacteria. Archaeal phylotypes included the Crenarchaea Desulfurococcus, Pyrobaculum, plus several unidentified hyperthermophilic lineages. A Methanothermococcus-like Euryarchaeon was also identified, with this genus not previously known from streamer communities. A multivariate approach to the analysis of biotic and abiotic data revealed that diversity patterns were best explained by a combination of temperature and sulphide rather than by any other abiotic variable either individually or in combination.

The distribution of cyanobacteria across physical and chemical gradients in hot springs in northern Thailand.

We mapped the distribution of mat forming cyanobacteria along the thermal gradient from 30 to 80 degrees C, in nine hot spring districts in northern Thailand. Nineteen genera and 36 species were identified by morphometric analysis. Water temperature was the predominant determinant of community structure in the springs. The diversity of cyanobacterial morphotypes fell as temperature increased. Water chemistry (pH, alkalinity and ammonia concentration) was a much weaker descriptor of the floral similarity between the springs. The morphotypes which dominated all springs were Synechococcus lividus and Synechococcus sp. (>40 and <80 degrees C) and Phormidium boryanum (>30 and <60 degrees C). The occurrence of Synechococcus lividus and Synechococcus sp. in every spring at 70 degrees C or more, implied there was no regional barrier to the distribution of these highly thermophilic taxa. Conversely, there were regional differences in the diversity of mat communities growing below 60 degrees C. The most depauperate flora were in the northernmost springs (SKP, TPN, PD, JS) and the springs further south around Chiang Mai had more diverse flora, suggestive of barriers to the dispersal of some taxa. More discriminating analyses using molecular tools will be required to determine whether the ubiquitous distribution Synechoccoccus morphotypes above 60 degrees C masks a genotypic diversity, comparable to the morphotype diversity observed below 60 degrees C.

Community phylogenetic analysis of moderately thermophilic cyanobacterial mats from China, the Philippines and Thailand.

Most community molecular studies of thermophilic cyanobacterial mats to date have focused on Synechococcus occurring at temperatures of approximately 50-65 degrees C. These reveal that molecular diversity exceeds that indicated by morphology, and that phylogeographic lineages exist. The moderately thermophilic and generally filamentous cyanobacterial mat communities occurring at lower temperatures have not previously been investigated at the community molecular level. Here we report community diversity in mats of 42-53 degrees C recovered from previously unstudied geothermal locations. Separation of 16S rRNA gene-defined genotypes from community DNA was achieved by DGGE. Genotypic diversity was greater than morphotype diversity in all mats sampled, although genotypes generally corresponded to observed morphotypes. Thirty-six sequences were recovered from DGGE bands. Phylogenetic analyses revealed these to form novel thermophilic lineages distinct from their mesophilic counterparts, within Calothrix, Cyanothece, Fischerella, Phormidium, Pleurocapsa, Oscillatoria and Synechococcus. Where filamentous cyanobacterial sequences belonging to the same genus were recovered from the same site, these were generally closely affiliated. Location-specific sequences were observed for some genotypes recovered from geochemically similar yet spatially separated sites, thus providing evidence for phylogeographic lineages that evolve in isolation. Other genotypes were more closely affiliated to geographically remote counterparts from similar habitats suggesting that adaptation to certain niches is also important.