Papers by Author: Guillermo Chong

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Authors: Lorena V. Escudero, Jonathan Bijman, Guillermo Chong, Juan Jose Pueyo, Cecilia Demergasso
Abstract: Acidic saline lake systems are an uncommon type of natural extreme environment described in Northern Chile and in Australia. These environments are considered a terrestrial analogue to certain ancient Martian terrains and a source of new material for biotechnological applications as bioleaching at high ionic strength conditions and biological systems for precipitating metal sulfides. The aim of this study is to describe the occurrence of redox couples that support prokaryotic life in the system and to obtain representative cultures of predominant microorganisms/metabolisms. Mapping of the area of interest and geochemical analysis of sediments, bedrock and water samples were performed. The original microbial community and enriched cultures were studied by direct count and culturing dependent and independent techniques. In the distal part of the alluvial fans some ponds are found with acidic brines (up to pH 1) of the Cl-SO4-Na (-Mg) type that are surrounded by yellow efflorescences. Other ponds towards the basin center progressively increase in concentration due to capillary evaporation. Brines are rich in aluminium and boron with lower concentration of manganese, lithium, iron and arsenic. An advanced hydrothermal argillic alteration affecting the country rocks, native sulfur associated to active solfataras, alunite and jarosite occurrences in sediments and chloride and sulfate efflorescent salts were evidenced. The microbial community in brines and sediments (105 and 106 cells/mL, respectively) was dominated by Firmicutes, Proteobacteria and Actinobacteria, and by Proteobacteria and Cyanobacteria, respectively. Sulphur and iron oxidation activity were detected depending on the salinity of the samples. Culture enrichments that respire and reduce As (V) and sulfate have been only obtained from sites with the highest pH (4-5). Microbial assemblages in those heterotrophic cultures were closely related to the Gamma and Betaproteobacteria, meanwhile, Rhodanobacter and Shewanella were the only microorganisms detected in the autotrophic cultures supplemented by Na2S and by H2. Relevant information to describe the occurring surface biogeochemical processes in that acidic saline system has been obtained. In addition, the occurrence of new prokaryotic genera capable of arsenic redox transformation has been evidenced in acidic systems.
Authors: Lorena Escudero, Jonathan Bijman, Guajardo M. Mariela, Juan José Pueyo Mur, Guillermo Chong, Cecilia Demergasso
Abstract: To understand the microbial community inhabiting in an acidic salt flat the phylogenetic diversity and the geochemistry of this system was compared to acid mine drainage (AMD) systems. The microbial community structure was assessed by DNA extraction/PCR/DGGE and secuencing for the 16S rRNA gene and the geochemistry was analyzed using several approaches. Prediction of metagenome functional content was performed from the 16S rRNA gene survey using the bioinformatics software package Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt). The geochemical results revealed a much lower iron concentration in the salt flat than in AMD systems (39 and 21804 mg L-1, respectively) and a significant difference in chloride levels. Sequences inferred to be from potential sulfur metabolizing organisms constituted up to 70% of the microbial community in the acidic salt flat meanwhile predominat iron-metabolizing acidophile populations were reported in AMD systems. Interestingly, the microbial assemblage in the acidic salt flat was dominated by mixotrophic and organotrophic sulfur oxidizers as well as by photoautotrophic acidophiles. Our results suggests that the salt concentration in Salar de Gorbea (average Cl-= 40 gL-1) is in the limit for the occurrence of chemolithotrophic oxidation of sulfur compounds. In addition, the investigation allows concluding that salinity rather than extremes of pH is the major environmental determinant of microbial community composition.
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