Enrichment of arsenic transforming and resistant heterotrophic bacteria from sediments of two salt lakes in Northern Chile

Abstract

Microbial populations are involved in the arsenic biogeochemical cycle in catalyzing arsenic transformations and playing indirect roles. To investigate which ecotypes among the diverse microbial communities could have a role in cycling arsenic in salt lakes in Northern Chile and to obtain clues to facilitate their isolation in pure culture, sediment samples from Salar de Ascotán and Salar de Atacama were cultured in diluted LB medium amended with NaCl and arsenic, at different incubation conditions. The samples and the cultures were analyzed by nucleic acid extraction, fingerprinting analysis, and sequencing. Microbial reduction of As was evidenced in all the enrichments carried out in anaerobiosis. The results revealed that the incubation factors were more important for determining the microbial community structure than arsenic species and concentrations. The predominant microorganisms in enrichments from both sediments belonged to the Firmicutes and Proteobacteria phyla, but most of the bacterial ecotypes were confined to only one system. The occurrence of an active arsenic biogeochemical cycle was suggested in the system with the highest arsenic content that included populations compatible with microorganisms able to transform arsenic for energy conservation, accumulate arsenic, produce H(2), H(2)S and acetic acid (potential sources of electrons for arsenic reduction) and tolerate high arsenic levels.

Distribution of Microbial Arsenic Reduction, Oxidation and Extrusion Genes along a Wide Range of Environmental Arsenic Concentrations

“…Bacterial fragments were amplified with the primer set 358FGC-907R [43] and DGGE was performed as described previously [43]. The bands were carefully excised from the DGGE gel with a razor blade under UV radiation for further identification as has been reported before [46]. Sequencing was carried out directly on PCR products with the 341F primer in Macrogen.…”

Arsenic metabolism in high altitude modern stromatolites revealed by metagenomic analysis

“…At the mentioned site, archaeal biofilms are capable of oxidizing As(III) and reducing As(V), a process that couples with energy generation, which was the first demonstration of the presence of these metabolisms in Haloarchaea 8 . Arsenic biogeochemical cycling was also shown to occur in other HAAL locations in Chile like Salar de Ascotán 16 , where some of the organisms involved were initially identified by enrichment cultures 17 . Later on, the genes involved in arsenic metabolism were prospected in a number of sites with arsenic concentrations spanning six orders of magnitude 18 .…”

Microbial Diversity in Sediment Ecosystems (Evaporites Domes, Microbial Mats, and Crusts) of Hypersaline Laguna Tebenquiche, Salar de Atacama, Chile

“…Bacterial and archaeal microorganisms inhabiting this lake are subject to extreme environmental conditions, such as high solar radiation (incl. UV), extreme diel temperature fluctuations, extreme changes in salinity due to net evaporation, and high lithium, boron, and arsenic concentrations (Lara et al, 2012; Farías et al, 2014). “Extreme” environmental conditions are generally conducive of microbial mat development (Rothschild and Mancinelli, 2001; Dupraz and Visscher, 2005) and a variety of photosynthetic organosedimentary ecosystems were found in Laguna Tebenquiche (Farías et al, 2014).…”