Abstract

The aim of this work was to determine environmental parameters and characterize prokaryotic communities in microbial mats along the thermal gradients of three unexplored hot springs from Chilean North Patagonia (Porcelana and Cahuelmó hot springs, and Porcelana Geyser), as part of an exploratory expedition. Physico-chemical data were obtained in situ (temperature, pH, conductivity and dissolved oxygen). Total and live bacterial counts were performed on fresh samples, and colony forming units of thermophilic heterotrophic aerobic bacteria were also determined. Results revealed total cell counts higher than in other hot springs (3.8 x 1012 cells per dry gram of mat, Cahuelmó), and a high percentage of thermophilic (55º C) culturable bacteria (20% of live cell counts in Geyser). Morphological analyses by SEM demonstrated the complexity and shifts in microbial mat structures along the thermal gradients of the three sites surveyed, i.e. filaments with and without sheaths (2 and 0.5 μm diameter sizes in average) dominated in different temperature ranges. Larger biovolume of thin filaments was found at higher temperatures. 16S rRNA gene fingerprinting analysis by denaturing gradient gel electrophoresis revealed five major phyla: Cyanobacteria, Chloroflexi, Bacteroidetes and Proteobacteria, and demonstrated changes in bacterial community composition along transects in each hot spring. A multidimensional scaling analysis showed that bacterial communities at high temperature had low resemblance to the corresponding mesophilic communities in each system; on the contrary, mesophilic communities were similar among hot springs. The data presented in this study are a first step to the analysis of these pristine hot springs.