EXTREME-HALOPHILES: THEIR ROLE IN THE ARSENIC BIOGEOCHEMICAL CYCLE

MARIA C. RASUK; OMAR F. ORDOÑEZ; MARIANA SORIA; FARÍAS, MARÍA EUGENIA

Córdoba

Congreso; XI Congreso Argentino de Microbiología General SAMIGE; 2015

Biofilms, mats and microbialites dwell under extreme environmental conditions (high salinity, extremearidity, pH and arsenic concentration) in the Argentinean Puna and the Atacama Desert. Microbialcommunities inhabiting those ecosystems are poorly known. Arsenic metabolism is proposed to be anancient mechanism in microbial life. Besides, some bacteria and archaea are not only able to usedetoxification processes to grow under high arsenic concentration, but also, some of them are able toexploit arsenic as a bioenergetic substrate in either anaerobic arsenate respiration orchemolithotrophic growth on arsenite. Only four aioAB and two arrA sequences from haloarchaeawere previously deposited in the NCBI Database, but have not been reported in the literature. ThearrA arsenate reductases are reliable indicators of anaerobic As (V) respiration and catalyze theelectron transfer to the As (V) terminal acceptor in dissimilatory arsenate-reducing prokaryotes(DARPs). In this work, we are presenting our first steps in the study of the arsenic biogeochemicalcycle in these ecosystems. Thus, the aim of this work was to isolate and to study the arsenicmetabolism genes of the isolated extreme halophile microorganisms as well as to test minimal mediausing different carbon sources. Mats and microbialites samples were taken from the water?s edge ofLaguna Tebenquiche, Laguna Brava (Salar de Atacama, Chile) during December 2012 and fromgaylusite crystals (Laguna Diamante) in August 2014. Samples were enriched and plated in WS mediasupplemented with arsenic (AsIII 0.5mM and AsV 20mM). Arsenite oxidase (aioB) and Arsenatereductase (arrA) primers specific for haloarchaea were designed using PrimerProspector software.Selected primers were aioB-1190F (5?-GCTCMTSACCGGCAGCGTCG-3?), aioB-1507R(5?-YGATCTCGTCGATGTCGGCG-3?), arrA-417F (5?-CCCGAGTTCGAGCCSATCTC-3?) andarrA-614R (5?-GCRCAGATCGMGCTGTGGGA-3?). In order to identify the isolates we usedArchaea-specific primers for 16S rDNA gene amplification: 344F (5´- ACG GGG YGC AGC AGG CGCGA-3´) and 915R (5´- GTG CTC CCC CGC CAA TTC CT -3´). Fragments of 577 bp, 317pb and 197pbwere obtained from 16S rDNA, aioB and arrA genes respectively. Universal primers 27F and 1492Rwere used to amplify 16S rDNA in bacterial isolates. 25 isolates belonging to Archaea and BacteriaDomain were obtained; they are related to the Phylum Euryarchaeota, Firmicutes and Proteobacteria.AioB and arrA genes were found in most of the isolates and DNA from the samples (mats,microbialites and biofilm). The best carbon source tested was pyruvate and acetate, being pyruvatebetter in all cases. Promising results were obtained in the search of organisms able to use arsenic intheir bioenergetic metabolism. More studies are underway to try to better understand these veryinteresting systems.