Extreme-halophiles: their role in the arsenic biogeochemical cycle?

MARIA CECILIA RASUK; OMAR F. ORDOÑEZ; MARIANA SORIA; MARIA EUGENIA FARIAS

Cordoba

Congreso; XI Congreso Argentino de Microbiología General (SAMIGE).; 2015

SAMIGE

Biofilms, mats and microbialites dwell underextreme environmental conditions (high salinity, extreme aridity, pH andarsenic concentration) in the Argentinean Puna and the Atacama Desert.Microbial communities inhabiting those ecosystems are poorly known. Arsenicmetabolism is proposed to be an ancient mechanism in microbial life. Besides,some bacteria and archaea are not only able to use detoxification processes togrow under high arsenic concentration, but also, some of them are able to exploitarsenic as a bioenergetic substrate in either anaerobic arsenate respiration orchemolithotrophic growth on arsenite. Only four aioAB coding for arseniteoxidase and two arrA coding for arsenate reductase sequences from haloarchaeawere previously deposited in the NCBI Database, but have not been reported inthe literature. The arrA arsenate reductases are reliable indicators ofanaerobic As (V) respiration and catalyze the electron transfer to the As (V)terminal acceptor in dissimilatory arsenatereducing prokaryotes (DARPs). Inthis work, we are presenting our first steps in the study of the arsenicbiogeochemical cycle in these ecosystems. Thus, the aim of this study was toisolate and to study the arsenic metabolism genes of the isolated extremehalophile microorganisms as well as to test the growth in minimal medium usingdifferent carbon sources. Mats and microbialites samples were taken from the water?sedge of Laguna Tebenquiche, Laguna Brava (Salar de Atacama, during December2012 and from gaylusite crystals (Laguna Diamante) in August 2014. Samples wereenriched and plated in WS medium supplemented with arsenic (AsIII 0.5mM and AsV20mM). Arsenite oxidase (aioB) and Arsenate reductase (arrA) primers specificfor haloarchaea were designed using PrimerProspector software. Selected primerswere 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 GGGYGC AGC AGG CGC GA-3 ́) and 915R (5 ́- GTG CTC CCC CGC CAA TTC CT -3 ́). Fragmentsof 577 bp, 317pb and 197pb were obtained from 16S rDNA, aioB and arrA genesrespectively. Universal primers 27F and 1492R were used to amplify 16S rDNA inbacterial isolates. 25 isolates belonging to Archaea and Bacteria Domain wereobtained; 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 pyruvateand acetate, being pyruvate better in all cases. Promising results were obtainedin the search of organisms able to use arsenic in their bioenergeticmetabolism. More studies are underway to try to better understand these veryinteresting systems.