MICROBIAL DIVERSITY IN AN EXTREME ANAEROBIC SEDIMENT FROM GEOTHERMAL CAVIAHUE?COPAHUE SYSTEM, NEUQUÉN, ARGENTINA

WILLIS PORATTI G.; DONATI E.R.

Congreso; SAMIGE 2014; 2014

The geothermal Copahue system is an extreme environment located in the north-west of Neuquén province, Argentina, at the foot of Copahue volcano. The area is characterized by a wide range of temperatures and pH values and the presence of heavy metals. Copahue is receiving an increasing amount of research within different areas like biogeochemistry, biotechnology (including bioleaching and bioremediation processes) and microbiology. Most work has been focused on aerobic, acidophilic sulfur- and iron-oxidizing bacteria and archaea. Relatively few studies have investigated the anaerobic zones of this environment. In this work we have examined the bacterial diversity focused on anaerobic prokaryotes in a sample taken in February 2012 in the hot spring sediment placed in Las Maquinitas (LMi) using a combination of molecular and cultivation techniques. Physicochemical parameters of Las Maquinitas sample were measured in situ: 90°C, pH 5, and a redox potential (EH) of -126 mV. The bacterial diversity of the sample was analyzed by a 16S rRNA gene bacterial clone library. The sequences obtained were compared with those in NCBI database using BLAST, and the phylogenetic affiliations of the clones determined by the ARB software package and using the Classifier tool of the Ribosomal Database Project (RDP). Several thermotolerant mesophilic and acidophilic bacteria were identified in this clone library and most of them are involved in the sulphur and iron cycles. Although PCR- based methods are not quantitative, Acidithiobacillus caldus seems to be the most abundant species found in the sample. These microorganisms can grow autotrophically ?and mixotrophically- using different sulphur compounds. This microorganism has been isolated from other geothermal sites and acid mine drainages. Thiomonas intermedia was also identified in LMi sample. Members of the genus Thiomonas are moderate acidophiles that oxidize reduced sulphur compounds. Other clones represented by Alicyclobacillus tolerans and Sulfobacillus thermotolerans were closely related to Firmicutes phylum. Among other characteristics, these bacteria are able to grow lithotrophically using iron(II) ions and/or sulphur compounds and/or heterotrophically using different organic substances. Most of them can form endospores which contribute to their resistant to high temperature values. Members of the genus Alicyclobacillus can also grow under facultative anaerobic conditions through iron(III) reduction. Other genera like Acidiphilum, Erythrobacter, and Thermoanaerobacterium were represented by only one clone. Although the negative EH of the environmental sample suggested the presence of sulphate-reducing bacteria, culture-independent techniques did not detect them. However, a mesophilic, spore-forming sulphate-reducer related to ?Desulfobacillus acidavidus? strain CL4 (99% sequence similarity) could be isolated from enrichment cultures at 30°C.