Molecular biomarkers in the subsurface of the Salar Grande (Atacama,Chile) evaporitic deposits

Denitrification in riparian wetlands plays a major role in eliminating nitrate coming from agricultural watershed uplands before they reach river water. A new approach was developed for representing this process in the biogeochemical Riverstrahler model, using a single adjustable parameter representing the potential denitrification rate of wetland soils. Applied to the case of three watersheds with contrasting size, land-use and hydro-climatic regime, namely the Seine and the Loir rivers (France) and the Red River (Vietnam), this new model is able to capture the general level of nitrate concentrations as well as their seasonal variations everywhere over the drainage network. The nitrogen budgets calculated from the results show that riparian denitrification eliminates between 10 and 50% of the diffuse sources of nitrogen into the hydrosystem coming from soil nitrate leaching.     

Archaeal diversity along a soil salinity gradient prone to disturbance

We employed a cultivation-independent approach to examine archaeal diversity along a transient soil salinity gradient at Salt Spring in British Columbia, Canada that is routinely eroded due to heavy, recurrent rainfall. Archaeal 16S rRNA gene libraries were created using DNA extracted from three soil samples collected along this gradient. Statistical comparisons indicated similar archaeal richness across sites but, a significant shift in archaeal community composition along the salinity gradient. Seven distinct phylogenetic groups were represented in soil libraries. Haloarchaea were the most commonly sampled group. Other 16S rRNA sequences were related to uncultured Euryarchaeota and Crenarchaeota or halophilic methanogens. Haloarchaeal diversity was remarkably high in soil of elevated salinity compared with previously characterized haloarchaeal communities. Salt Spring haloarchaea were not closely related to known low-salt adapted/tolerant species, suggesting they may be frequently faced with local mortality as a result of frequent declines in soil salinity. We speculate that ecosystem disturbance -- in the form of salinity fluctuations -- is one mechanism for maintaining a diverse community of haloarchaea at Salt Spring.     

Prokaryotic diversity and biogeochemical characteristics of field living and laboratory cultured stromatolites from the hypersaline Laguna Interna,Salar de Atacama (Chile)

Extremophiles - Stromatolites are organo-sedimentary structures found principally in seas and saline lakes that contain sheets of sediments and minerals formed by layers of microbial communities,...     

Biomineralization of Carbonates by Marinococcus albus and Marinococcus halophilus Isolated from the Salar de Atacama (Chile)

We studied the precipitation of carbonates in 17 strains of moderately halophilic, Gram-positive cocci belonging to two species: Marinococcus halophilus and Marinococcus albus, isolated from the Salar de Atacama (Chile). They were cultivated in solid and liquid laboratory media for 42 days at salt concentrations (wt/vol) of 3%, 7.5%, 15%, and 20%. The bioliths precipitated were studied by X-ray diffraction and scanning electron microscopy. M. halophilus formed crystals at each of the salt concentrations, with a maximum number of strains capable of precipitating carbonates at 7.5% and 15% salt concentrations. M. albus did not precipitate at 20% and showed a maximum at 7.5%. This behavior is similar to that of other Gram-positive bacteria and differs from that found in Gram-negative bacteria. The bioliths precipitated were spherical, generally isolated, with a size of 10–100 μm, varying with salinity. They were of magnesium calcite (CO₃ Ca_1-x Mg_x) with Mg content increasing with increasing salinity and Mg/Ca molar ratio of the culture medium. These results demonstrate the active role played by M. halophilus and M. albus in the precipitation of carbonates. Received: 3 November 1998 / Accepted: 9 March 1999     

Prokaryotic diversity and community composition in the Salar de Uyuni,a large scale,chaotropic salt flat

Salar de Uyuni (SdU), with a geological history that reflects 50 000 years of climate change, is the largest hypersaline salt flat on Earth and is estimated to be the biggest lithium reservoir in the world. Its salinity reaches saturation levels for NaCl, a kosmotropic salt, and high concentrations of MgCL₂ and LiCl, both salts considered important chaotrophic stressors. In addition, extreme temperatures, anoxic conditions, high UV irradiance, high albedo and extremely low concentrations of phosphorous, make SdU a unique natural extreme environment in which to contrast hypotheses about limiting factors of life diversification. Geophysical studies of brines from different sampling stations show that water activity is rather constant along SdU. Geochemical measurements show significant differences in magnesium concentration, ranging from 0.2 to 2M. This work analyses the prokaryotic diversity and community structure at four SdU sampling stations, selected according to their location and ionic composition. Prokaryotic communities were composed of both Archaea (with members of the classes Halobacteria, Thermoplasmata and Nanohaloarchaea, from the Euryarchaeota and Nanohaloarcheota phyla respectively) and Bacteria (mainly belonging to Bacteroidetes and Proteobacteria phyla). The important differences in composition of microbial communities inversely correlate with Mg²⁺ concentration, suggesting that prokaryotic diversity at SdU is chaotropic dependent.     

Microbial community composition and trophic role along a marked salinity gradient in Laguna Puilar,Salar de Atacama,Chile

The geological, hydrological and microbiological features of the Salar de Atacama, the most extensive evaporitic sedimentary basin in the Atacama Desert of northern Chile, have been extensively studied. In contrast, relatively little attention has been paid to the composition and roles of microbial communities in hypersaline lakes which are a unique feature in the Salar. In the present study biochemical, chemical and molecular biological tools were used to determine the composition and roles of microbial communities in water, microbial mats and sediments along a marked salinity gradient in Laguna Puilar which is located in the “Los Flamencos” National Reserve. The bacterial communities at the sampling sites were dominated by members of the phyla Bacteroidetes, Chloroflexi, Cyanobacteria and Proteobacteria. Stable isotope and fatty acid analyses revealed marked variability in the composition of microbial mats at different sampling sites both horizontally (at different sites) and vertically (in the different layers). The Laguna Puilar was shown to be a microbially dominated ecosystem in which more than 60% of the fatty acids at particular sites are of bacterial origin. Our pioneering studies also suggest that the energy budgets of avian consumers (three flamingo species) and dominant invertebrates (amphipods and gastropods) use minerals as a source of energy and nutrients. Overall, the results of this study support the view that the Salar de Atacama is a heterogeneous and fragile ecosystem where small changes in environmental conditions may alter the balance of microbial communities with possible consequences at different trophic levels.     

Characterization of a Chlorophyta microalga isolated from a microbial mat in Salar de Atacama (northern Chile) as a potential source of compounds for biotechnological applications

Microalgae are an important source of unsaturated fatty acids, phospholipids, glycolipids, and carotenes, which are useful compounds for the food and pharmaceutical industries. The Atacama Desert of northern Chile is one of the driest deserts on Earth and, as such, it is a great natural laboratory in which to study new microorganisms adapted to extreme environments. A microalgal strain, referred to here as CH03, was isolated from a microbial mat in salt flat water in Salar de Atacama. Genetic analysis of the 18S ribosomal RNA gene showed that the strain had homology with other known sequences of the species Chlorella sorokiniana. Our results revealed the adaptability of this microalga to freshwater medium under laboratory conditions, despite coming from an extremely high‐salinity environment. The fatty acid profile of CH03(A) newly isolated in Bold's basal medium differed from that of CH03(B) cultured in vitro in modified F/2 medium and from another five strains of C. sorokiniana and three strains of Chlorella vulgaris in that it had a high stearic acid content and had no polyunsaturated fatty acids. The major biochemical components observed in this strain were proteins (64.3–73.6%) and lipids (26.6–32.6%). This study suggests that the strain CH03 could be a protein source and that this oleaginous microalga is easy to grow in vitro as a biological model for future studies.     

Taxonomic study of extreme halophilic archaea isolated from the "Salar de Atacama", Chile

A large number of halophilic bacteria were isolated in 1984-1992 from the Atacama Saltern (North of Chile). For this study 82 strains of extreme halophilic archaea were selected. The characterization was performed by using the phenotypic characters including morphological, physiological, biochemical, nutritional and antimicrobial susceptibility test. The results, together with those from reference strains, were subjected to numerical analysis, using the Simple Matching (S(SM)) coefficient and clustered by the unweighted pair group method of association (UPGMA). Fifteen phena were obtained at an 70% similarity level. The results obtained reveal a high diversity among the halophilic archaea isolated. Representative strains from the phena were chosen to determine their DNA base composition and the percentage of DNA-DNA similarity compared to reference strains. The 16S rRNA studies showed that some of these strains constitutes a new taxa of extreme halophilic archaea.     

Archaeal diversity in naturally occurring and impacted environments from a tropical region

AIMS: To evaluate archaeal diversity in natural and impacted habitats from Rio de Janeiro state, Brazil, a tropical region of South America. METHODS AND RESULTS: 16S rRNA gene was amplified directly by polymerase chain reaction (PCR) from genomic DNA, extracted from Guanabara Bay (GB) water, halomarine sediment (HS), municipal landfill leachate, agricultural soil and wastewater treatment (WT) system. Five archaeal 16S rDNA clone libraries were constructed. A total of 123 clones, within the five libraries analysed, were clustered into 29 operational taxonomic units, related to cultivated (24%) and uncultivated (76%) organisms. Rarefaction analysis showed that the libraries contained different levels of diversity. PCR-denaturing gradient gel electrophoresis (DGGE) of 16S-23S intergenic spacer regions confirmed the presence of a dominant phylotype, revealed by the WT system clone library. CONCLUSIONS: Archaeal communities of impacted environments seem to be confined to specific ecosystems with similar physicochemical properties, while communities from natural environments appear to be widely distributed. The presence of a high number of phylotypes related to uncultivated organisms suggests new archaeal lineages. SIGNIFICANCE AND IMPACT OF THE STUDY: This study reports, for the first time, the analysis of archaeal diversity in tropical environments from Brazil, and adds sequences from this region to the developing database of 16S rRNA clone libraries from environmental samples.     

Size variation ofAcacia caven (leguminosae) pods along a climatic gradient in Chile

A southward tendency of increment in pod-length is shown for 11 populations ofAcacia caven (Mol.) Hook et Arn. localized along a climatic gradient of increasing annual rainfall in Chile. This fact would suggest thatA. caven populations occurring in the south are in better conditions for reproduction than northern populations, since pod-length is related to the amount of seeds inside the pods. The possible bearing of this southward tendency of increasing seed production upon the expansion ofA. caven toward the more humid zones in southern Chile is discussed.     

Distribution of greenhouse gases in hyper-arid and arid areas of northern Chile and the contribution of the high altitude wetland microbiome (Salar de Huasco,Chile)

Northern Chile harbors different bioclimatic zones including hyper-arid and arid ecosystems and hotspots of microbial life, such as high altitude wetlands, which may contribute differentially to greenhouse gases (GHG) such as carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O). In this study, we explored ground level GHG distribution and the potential role of a wetland situated at 3800 m.a.s.l, and characterized by high solar radiation <?1600 W m^?2, extreme temperature ranges (?12 to 24 °C) and wind stress (<?17 m s^?1). The water source of the wetland is mainly groundwater springs, which generates streams and ponds surrounded by peatlands. These sites support a rich microbial aquatic life including diverse bacteria and archaea communities, which transiently form more complex structures, such as microbial mats. In this study, GHG were measured in the water and above ground level air at the wetland site and along an elevation gradient in different bioclimatic areas from arid to hyper-arid zones. The microbiome from the water and sediments was described by high-throughput sequencing 16S rRNA and rDNA genes. The results indicate that GHG at ground level were variable along the elevation gradient potentially associated with different bioclimatic zones, reaching high values at the high Andean steppe and variable but lower values in the Atacama Desert and at the wetland. The water areas of the wetland presented high concentrations of CH₄ and CO₂, particularly at the spring areas and in air bubbles below microbial mats. The microbial community was rich (>?40 phyla), including archaea and bacteria potentially active in the different matrices studied (water, sediments and mats). Functional microbial groups associated with GHG recycling were detected at low frequency, i.e., <?2.5% of total sequences. Our results indicate that hyper-arid and arid areas of northern Chile are sites of GHG exchange associated with various bioclimatic zones and particularly in aquatic areas of the wetland where this ecosystem could represent a net sink of N₂O and a source for CH₄ and CO₂.     

Field evaluation of potential control strategies against the invasive eastern subterranean termite (Isoptera: Rhinotermitidae) in Chile

Four different termite control strategies consisting of two soil treatments with cypermethrin and fipronil and two bait treatments with hexaflumuron and sulfluramid were evaluated for their efficacy and potential for controlling the invasive eastern subterranean termite, Reticulitermes flavipes (Kollar) (Isoptera: Rhinotermitidae), in Quillota and Valparaiso, Chile. Monitoring stations were installed at all sites to measure the overall termite activity next to and at distances up to 30 m away from infested structures, most being 3-5 m. Foraging activity was extremely seasonal with the maximum consumption rates occurring from January to April. Termite foraging activity was low from July to September. After treatments in January 2003, there was a significant decrease in wood consumption, percentage of active stations, and numbers of termites in traps for the first 6 mo with hexaflumuron baits. No significant change in R. flavipes foraging activity was observed on wood consumption and percentage of active stations for sulfluramid bait or cypermethrin and fipronil soils treatments. The seasonal pattern of foraging activity remained unchanged for all treatments in 2004 and 2005, except structures baited with hexaflumuron. Feeding activity at the monitors in the area surrounding the hexaflumuron baits declined to 0 after January 2004. Alate flights occurred in approximately 38% of the structures treated with cypermethrin and sulfluramid bait in 2003 and in approximately 40% of the structures treated with cypermethrin, fipronil, and sulfluramid bait in 2004. Sulfluramid baits and cypermethrin soil treatments did not have any impact within a 15-m radius of the structures. Soils treatments of fipronil and cypermethrin prevented termites access in 75% of the homes. The number of active monitoring stations only declined within 2 m of the fipronil-treated zone. Hexaflumuron exhibited a reduction in activity for at least a 15-m radius.     

Genetic diversity of the subterranean Gansu zokor in a semi-natural landscape

We studied the relationship between genetic diversity of the subterranean Gansu zokor Myospalax cansus and habitat variability in the Loess Plateau, Qinghai Province, China. We used a combination of geographic information systems and molecular techniques to assess the impact of habitat composition and human activities on the genetic diversity of zokor populations in this semi-natural landscape. Although they occurred relatively infrequently in the landscape, woodland and high-coverage grassland habitats were the main positive contributors to the genetic diversity of zokor populations. Rural residential land, plain agricultural land and low-coverage grassland had a negative effect on genetic diversity. Hilly agricultural land and middle-coverage grassland had little impact on zokor genetic diversity. There were also interactions between some habitat types, that is, habitat types with relatively better quality together promoted conservation of genetic diversity, while the interaction between (among) bad habitat types made situations worse. Finally, habitat diversity, measured as patch richness and Shannon's diversity index, was positively correlated with the genetic diversity. These results demonstrated that: (1) different habitat types had different effects on the genetic diversity of zokor populations and (2) habitat quality and habitat heterogeneity were important in maintaining genetic diversity. Habitat composition was closely related to land use thus emphasizing the importance of human activities on the genetic diversity of subterranean rodent populations in this semi-natural landscape. Although the Gansu zokor was considered to be a pest species in the Loess Plateau, our study provides insights for the management and conservation of other subterranean rodent species.     

Molecular analysis of enrichment cultures of ammonia oxidizers from the Salar de Huasco,a high altitude saline wetland in northern Chile

We analyzed enrichment cultures of ammonia-oxidizing bacteria (AOB) collected from different areas of Salar de Huasco, a high altitude, saline, pH-neutral water body in the Chilean Altiplano. Samples were inoculated into mineral media with 10 mM NH₄ ⁺ at five different salt concentrations (10, 200, 400, 800 and 1,400 mM NaCl). Low diversity (up to three phylotypes per enrichment) of beta-AOB was detected using 16S rDNA and amoA clone libraries. Growth of beta-AOB was only recorded in a few enrichment cultures and varied according to site or media salinity. In total, five 16S rDNA and amoA phylotypes were found which were related to Nitrosomonas europaea/Nitrosococcus mobilis, N. marina and N. communis clusters. Phylotype 1-16S was 97% similar with N. halophila, previously isolated from Mongolian soda lakes, and phylotypes from amoA sequences were similar with yet uncultured beta-AOB from different biofilms. Sequences related to N. halophila were frequently found at all salinities. Neither gamma-AOB nor ammonia-oxidizing Archaea were recorded in these enrichment cultures.     

Microbial colonization of the salt deposits in the driest place of the Atacama Desert (Chile)

The Atacama Desert (Chile), one of the most arid places on Earth, shows hostile conditions for the development of epilithic microbial communities. In this study, we report the association of cyanobacteria (Chroococcidiopsis sp.) and bacteria belonging to Actinobacteria and Beta-Gammaproteobacteria and Firmicutes phyla inhabiting the near surface of salt (halite) deposits of the Salar Grande Basin, Atacama Desert (Chile). The halite deposits were investigated by using optical, confocal and field emission scanning electron microscopes, whereas culture-independent molecular techniques, 16S rDNA clone library, alongside RFLP analysis and 16S rRNA gene sequencing were applied to investigate the bacterial diversity. These microbial communities are an example of life that has adapted to extreme environmental conditions caused by dryness, high irradiation, and metal concentrations. Their adaptation is, therefore, important in the investigation of the environmental conditions that might be expected for life outside of Earth.     

Latitudinal patterns and regionalization of plant diversity along a 4270‐km gradient in continental Chile

According to the global latitudinal diversity gradient, a decrease in animal and plant species richness exists from the tropics towards higher latitudes. The aim of this study was to describe the latitudinal distribution patterns of Chilean continental flora and delineate biogeographic regions along a 4270‐km north–south gradient. We reviewed plant lists for each of the 39 parallels of continental Chile to build a database of the geographical distribution of vascular plant species comprising 184 families, 957 genera and 3787 species, which corresponded to 100%, 94.9% and 74.2% of the richness previously defined for Chile, respectively. Using this latitudinal presence–absence species matrix, we identified areas with high plant richness and endemism and performed a Cluster analysis using Jaccard index to delineate biogeographic regions. This study found that richness at family, genus and species levels follow a unimodal 4270‐km latitudinal distribution curve, with a concentration of richness in central Chile (31–42°S). The 37th parallel south (central Chile) presented the highest richness for all taxonomic levels and in specific zones the endemism (22–37°S) was especially high. This unimodal pattern contrasts the global latitudinal diversity gradient shown by other studies in the Northern hemisphere. Seven floristic regions were identified in this latitudinal gradient: tropical (18–22°S), north Mediterranean (23–28°S), central Mediterranean (29–32°S), south Mediterranean (33–37°S), north temperate (38–42°S), south temperate (43–52°S) and Austral (53–56°S). This regionalization coincides with previous bioclimatic classifications and illustrates the high heterogeneity of the biodiversity in Chile and the need for a reconsideration of governmental conservation strategies to protect this diversity throughout Chile.     

Carabidae diversity along an altitudinal gradient in a Peruvian cloud forest (Coleoptera)

Carabid beetles were sampled at five sites, ranging from 1500 m to 3400 m, along a 15 km transect in the cloud forest of Manu National Park, Perú. Seasonal collections during a one year period yielded 77 morphospecies, of which 60% are projected to be undescribed species. There was a significant negative correlation between species richness and altitude, with the number of carabid species declining at the rate of one species for each 100 m increase in altitude. The majority of species (70.1 %) were restricted to only one altitudinal site and no species was found at more than three of the five altitudinal sites. Only one genus, Pelmatellus (Tribe Harpalini), was found at all five sites. Active (hand) collections yielded approximately twice as many species per individuals collected than passive (pitfall trap) collections. This study is the first systematic sampling ofcarabid beetles of a high altitude gradient in the cloud forests of southeastern Perú and supports the need to conserve the zone of extremely high biodiversity present on the eastern slopes of the Peruvian Andes.     

Evidence for speciation underground in diving beetles (Dytiscidae) from a subterranean archipelago

Most subterranean animals are assumed to have evolved from surface ancestors following colonization of a cave system; however, very few studies have raised the possibility of “subterranean speciation” in underground habitats (i.e., obligate cave‐dwelling organisms [troglobionts] descended from troglobiotic ancestors). Numerous endemic subterranean diving beetle species from spatially discrete calcrete aquifers in Western Australia (stygobionts) have evolved independently from surface ancestors; however, several cases of sympatric sister species raise the possibility of subterranean speciation. We tested this hypothesis using vision (phototransduction) genes that are evolving under neutral processes in subterranean species and purifying selection in surface species. Using sequence data from 32 subterranean and five surface species in the genus Paroster (Dytiscidae), we identified deleterious mutations in long wavelength opsin (lwop), arrestin 1 (arr1), and arrestin 2 (arr2) shared by a sympatric sister‐species triplet, arr1 shared by a sympatric sister‐species pair, and lwop and arr2 shared among closely related species in adjacent calcrete aquifers. In all cases, a common ancestor possessed the function‐altering mutations, implying they were already adapted to aphotic environments. Our study represents one of the first confirmed cases of subterranean speciation in cave insects. The assessment of genes undergoing pseudogenization provides a novel way of testing modes of speciation and the history of diversification in blind cave animals.     

Archaeal and bacterial diversity in two hot spring microbial mats from a geothermal region in Romania

The diversity of archaea and bacteria was investigated in two slightly alkaline, mesophilic hot springs from the Western Plain of Romania. Phylogenetic analysis showed a low diversity of Archaea, only three Euryarchaeota taxa being detected: Methanomethylovorans thermophila, Methanomassiliicoccus luminyensis and Methanococcus aeolicus. Twelve major bacterial groups were identified, both springs being dominated by Cyanobacteria, Chloroflexi and Proteobacteria. While at the phylum/class-level the microbial mats share a similar biodiversity; at the species level the geothermal springs investigated seem to be colonized by specific consortia. The dominant taxa were filamentous heterocyst-containing Fischerella, at 45 °C and non-heterocyst Leptolyngbya and Geitlerinema, at 55 °C. Other bacterial taxa (Thauera sp., Methyloversatilis universalis, Pannonibacter phragmitetus, Polymorphum gilvum, Metallibacterium sp. and Spartobacteria) were observed for the first time in association with a geothermal habitat. Based on their bacterial diversity the two mats were clustered together with other similar habitats from Europe and part of Asia, most likely the water temperature playing a major role in the formation of specific microbial communities that colonize the investigated thermal springs.     

Intraregional variation among Alexandrium catenella (Dinophyceae) strains from southern Chile: Morphological,toxicological and genetic diversity

Morphological, toxicological and phylogenetic analyses, using the partial LSU gene and internal spacer (ITS) regions of the rDNA gene, were combined to evaluate the intraregional diversity of Alexandrium catenella occurring along the southern coast of Chile. Twenty-two strains isolated from different localities along the wide area of distribution of the species (from 42°S to 55°S) were examined by these three approaches. Morphologically, although the strains showed diagnostic characters according to the species definition, variations in these traits within and between strains were also observed. The absence of an apical or posterior attachment pore, for instance, was observed mainly in old isolates. Indirect connection between the apical and 1′ plates, traits normally seen in other species of the same genus, was also noted in some strains. However, the lack of a ventral pore on the 1′ plate was one of the most distinctive characteristics present in all the Chilean strains. Toxicologically, the Chilean strains were characterized by the dominance of N-sulfocarbamate (C1,2) and gonyautoxins (GTX1–4), but also by the scarcity or absence of saxitoxin. Considering the dominance of these toxins in each strain, at least two distinctive toxin patterns were distinguished. Through rDNA sequence analysis, the Chilean strains were segregated as part of Clade I (North American) of the Alexandrium tamarense species complex. Nevertheless, significant genetic diversity was also observed among the Chilean strains, especially using ITS sequences. Through these three approaches, Chilean strains of A. catenella showed significant intraregional variability, which is appropriate for a native species. However, the distribution of its genetic diversity seems to be inconsistent with the apparent northward expansion observed along the west coast of South America.