Water Microbial Communities Research Articles

Algae and Clay Water Additives Differentially Impact Survival and Microbial Community Structure in Sablefish (Anoplopoma fimbria) Rearing Tanks

Algae, or “greenwater,” is a traditional water additive used in finfish aquaculture, but is associated with high costs and potentially harmful bacterial growth. “Claywater,” a mix of clay and seawater, has been explored as a replacement for greenwater. In some fish species, however, claywater reduces survival rates, but the mechanisms are not understood. A link between water additive and microbial community composition may exist. In this study, the effects of different water additives on the microbial communities of larval sablefish were studied. Three treatments were evaluated: a traditional greenwater additive, a claywater additive, and a greenwater additive switched to claywater after one week. Microbial communities were characterized using 16S rRNA gene sequencing, and sablefish survival and growth were recorded. Tank seawater microbial communities were significantly influenced by water additive (treatment). Sablefish microbiomes were significantly, but weakly influenced by treatment, and there were time-specific differences within the claywater treatment. Sablefish from the treatment that was switched after one week maintained microbiomes that were more similar to the initial greenwater treatment. In general, sablefish were dominated by Vibrionaceae OTUs. Variability in the sablefish microbiomes between tanks from the same treatment was high, especially in the claywater treatment, which may have confounded treatment effects. Larvae in the claywater treatment had significantly lower survival rates compared to greenwater and greenwater-claywater treatments, but no treatment effect was observed on sablefish growth (length). Overall, results suggest that claywater does not negatively impact survival or the microbial community of sablefish when preceded by one week of greenwater.

Metagenomic analysis of composition, function and cycling processes of microbial community in water, sediment and effluent of Litopenaeus vannamei farming environments under different culture modes

With the increasing production of farmed Litopenaeus vannamei, the discharge of culture sewage and the accumulation of deleterious substances (nitrite, ammonia, sulfide…) in ponds have been more severe, especially at the mid-late farming stage, severely inhibiting the sustainability of aquaculture. Considering vital roles of microorganisms in cycling processes, we thereupon comprehensively investigated microbiotas in water, sediment and effluent of L. vannamei ponds under different culture modes by 16S rRNA gene and metagenome sequencing. Results revealed that microbial communities in water, sediment and effluent of white shrimp ponds were diverse and had active metabolism. Genes related to quorum sensing were abundant. Furthermore, we uncovered carbon fixation, such as CBB, WL and 3-HP; N, S, P cycling except nitrification and sulfide oxidation were active in shrimp farming environments at mid-late farming stage. Remarkably, each gene encoding key enzyme involved in cycling processes was assigned to specific taxa, such as Rhodobacteraceae, Rubrivivax and so on. Interestingly, many functional taxa (Vibrio, Aeromonas) were also potential pathogens to shrimp and microbiotas' structure along with function were correlated with environmental factors, reminding us of regulating variations of environmental factors during the shrimp farming period. Meanwhile, water, sediment and effluent under different culture modes had different microbial diversity and characteristics. Notably, we called for urgent management of direct discharge of aquaculture sewage including numerous genes related to human diseases, which is vital to public health. Briefly, this was the first study analyzing microbiotas' structure, function, ecology cycling in different L. vannamei culture surroundings and their correlation with environmental factors, advancing our knowledge for aquaculture ecosystems and providing preliminary data for probiotics screening and cycling regulation in the future.

Microbial Community of Saline, Alkaline Lakes in the Nebraska Sandhills Based on 16S rRNA Gene Amplicon Sequence Data.

The Nebraska Sandhills region contains over 1,500 geochemically diverse interdunal lakes, some of which are potassium rich, alkaline, and hypersaline. Here, we report 16S rRNA amplicon pyrosequencing data on the water and sediment microbial communities of eight alkaline lakes in the Sandhills of western Nebraska.

Metatranscriptomic exploration of microbial functioning in clouds

Clouds constitute the uppermost layer of the biosphere. They host diverse communities whose functioning remains obscure, although biological activity potentially participates to atmospheric chemical and physical processes. In order to gain information on the metabolic functioning of microbial communities in clouds, we conducted coordinated metagenomics/metatranscriptomics profiling of cloud water microbial communities. Samples were collected from a high altitude atmospheric station in France and examined for biological content after untargeted amplification of nucleic acids. Living microorganisms, essentially bacteria, maintained transcriptional and translational activities and expressed many known complementary physiological responses intended to fight oxidants, osmotic variations and cold. These included activities of oxidant detoxification and regulation, synthesis of osmoprotectants/cryoprotectants, modifications of membranes, iron uptake. Consistently these energy-demanding processes were fueled by central metabolic routes involved in oxidative stress response and redox homeostasis management, such as pentose phosphate and glyoxylate pathways. Elevated binding and transmembrane ion transports demonstrated important interactions between cells and their cloud droplet chemical environments. In addition, polysaccharides, potentially beneficial for survival like exopolysaccharides, biosurfactants and adhesins, were synthesized. Our results support a biological influence on cloud physical and chemical processes, acting notably on the oxidant capacity, iron speciation and availability, amino-acids distribution and carbon and nitrogen fates.

Impacts of solids retention time and antibiotic loading in activated sludge systems on secondary effluent water quality and microbial community structure.

Solids retention time (SRT) is one of the most important factors in designing and operating activated sludge systems for biological wastewater treatment. Longer SRTs have been shown to alter the structure and function of microbial communities, thereby leading to improved treatment efficacy with respect to bulk and trace organics, nutrient removal, and membrane fouling. Research has also shown that longer SRTs and/or higher influent antibiotic concentrations may lead to increased prevalence of antibiotic resistance. However, it is unclear whether elevated, yet subclinical, concentrations of antibiotics also impact the overall microbial community. The purpose of this study was to characterize changes in microbial community structure in a laboratory-scale activated sludge system as a function of SRT (2-20days) and influent concentrations (1×-100× ambient) of ampicillin, sulfamethoxazole, tetracycline, trimethoprim, and vancomycin. Changes in microbial community structure were evaluated based on 16S rRNA gene sequencing, and microbial community function was evaluated based on changes in effluent water quality, including attenuation of bulk and trace organics. The results confirmed that longer SRTs-but not antibiotic loadings-had a significant impact on microbial community structure and effluent water quality. Therefore, moderate spikes in influent antibiotic concentrations are not expected to adversely impact biological wastewater treatment. PRACTITIONER POINTS: Longer SRTs lead to changes in microbial community structure, including alpha and beta diversity and relative abundance of various taxa. Enhanced TOrC attenuation at longer SRTs may be linked to biomass abundance rather than changes in microbial community structure. Moderate spikes in influent antibiotic concentrations do not impact activated sludge performance or microbial community structure. The phyla Proteobacteria and Bacteroidetes comprise a majority of the microbial community in primary effluent and mixed liquor.

Water Quality and Microbial Community Changes in an Urban River after Micro-Nano Bubble Technology in Situ Treatment

Currently, black-odor river has received great attention in China. In this study, the micro-nano bubble technology (MBT) was used to mitigate the water pollution rapidly and continuously by increasing the concentration of dissolved oxygen (DO) in water. During treatment, the concentration of DO increased from 0.60 mg/L to over 5.00 mg/L, and the oxidation reduction potential (ORP) also changed from a negative value to over 100.00 mV after only five days aeration. High throughput pyrosequencing technology was employed to identify the microbial community structure. At genus level, the dominant bacteria were anaerobic and nutrient-loving microbes (e.g., Arcobacter sp., Azonexus sp., and Citrobacter sp.) before, and the relative abundances of aerobic and functional microbes (e.g., Perlucidibaca sp., Pseudarcicella sp., Rhodoluna sp., and Sediminibacterium sp.) were increased after treatment. Meanwhile, the water quality was significantly improved with about 50% removal ratios of chemical oxygen demand (CODCr) and ammonia nitrogen (NH4+-N). Canonical correspondence analysis (CCA) results showed that microbial community structure shaped by COD, DO, NH4+-N, and TP, CCA1 and CCA2 explained 41.94% and 24.56% of total variances, respectively. Overall, the MBT could improve the water quality of urban black-odor river by raising the DO and activate the aerobic microbes.

River Ganges water as reservoir of microbes with antibiotic and metal ion resistance genes: High throughput metagenomic approach

The large scale usage of antibiotics and trace elements leads to their progressive release in the environment, and ultimately the spread of antibiotic resistance genes (ARGs) and metal ion resistance genes (MRGs) in bacteria. A high-throughput metagenomic sequencing of the microbial community in water and sediments in the river Ganges harboring resistance genes was performed. The results revealed that the river harbors a broad spectrum of resistance genes with high abundance in sediments. The highly dominant ARGs type was beta-lactam, multidrug/efflux and elfamycin. The ARGs such as (tuf, parY, ileS, mfd) were highly abundant in water and sediments. The MRGs subtype acn was the most abundant metal resistance gene in water and sediments. Majority of ARGs types showed significant (p ≤ 0.05) positive correlation with the MRGs types in the river environment suggesting their distribution and transfer to be possibly linked. Taxonomic classification revealed that Proteobacteria and Actinobacteria were the two most abundant phyla in water and sediments. Arcobacter, Terrimicrobium, Acidibacter and Pseudomonas were the most abundant genera. This study suggests that antibiotics and metals are the driving force for the emergence of resistance genes, and their subsequent propagation and accumulation in the environmental bacteria. The present metagenomic investigation highlights significance of such study, and attracts attention for the mitigation of pollutants associated with the propagation of ARGs and MRGs in the river environment.

Removal Efficacy of Opportunistic Pathogens and Bacterial Community Dynamics in Two Drinking Water Treatment Trains.

Drinking water treatment processes (DWTPs) impact pathogen colonization and microbial communities in finished water; however, their efficacies against opportunistic pathogens are not fully understood. In this study, the effects of treatment steps on the removal of Legionella spp., Legionella pneumophila, nontuberculous mycobacteria, Mycobacterium avium, and two amoeba hosts (Vermamoeba vermiformis, Acanthamoeba) are evaluated in two parallel trains of DWTPs equipped with different pretreatment units. Quantitative polymerase chain reaction analysis demonstrates significantly reduced numbers of total bacteria, Legionella, and mycobacteria during ozonation, followed by a rebound in granular activated carbon (GAC) filtration, whereas sand filtration exerts an overarching effect in removing microorganisms in both treatment trains. V. vermiformis is more prevalent in biofilm (34%) than water samples (7.7%), while Acanthamoeba is not found in the two trains of DWTPs. Illumina sequencing of bacterial 16S rRNA genes reveals significant community shifts at different treatment steps, as well as distinct bacterial community structures in water and biofilm samples in parallel units (e.g., ozonation, GAC, sand filtration) between the two trains (analysis of similarities (ANOSIM), p < 0.05), implying the potential influence of different pretreatment steps in shaping the downstream microbiome. Overall, the results provide insights to mitigation of opportunistic pathogens and engineer approaches for managing bacterial communities in DWTPs.

Drinking water bacterial communities exhibit specific and selective necrotrophic growth

Physicochemical water disinfection methods result in the reduction of bacterial concentrations by orders of magnitude, but not in the total elimination of the bacterial community. As such, the dead bacterial biomass may act as a carbon and nutrient source for the survivor populations. The ability of bacterial strains to grow on dead bacterial cells has been described before as necrotrophy. We investigated the impact of killed bacterial biomass of two different bacterial strains on the growth potential of natural drinking water microbial communities. Many indigenous bacterial taxa could grow on dead biomass, with the total bacterial concentration increasing from 104 to 108 cells/ml. Necrotrophic growth was specific (43 enriched taxa) and selective (i.e. enriched taxa were dependent on the type of dead biomass). The potential of natural water communities to grow necrotrophically has remained underexplored. Nevertheless the phenomenon can have a big impact in water quality and deserves more attention.

Site-specific differences in microbial community structure and function within the rhizosphere and rhizoplane of wetland plants is plant species dependent

Two types of organisms that are vital to the ecosystem services provided by wetlands are plants and soil microorganisms, more specifically, the bacteria associated with the roots of wetland plants. In order to better understand the relationships between wetland plants and their associated microorganisms, we tested the hypothesis that the microbial rhizosphere and rhizoplane communities in wetland systems highly impacted by anthropogenic activities subjected to poor water quality inputs would differ from those communities in areas less impacted by anthropogenic activity receiving higher water quality inputs. To test this hypothesis we compared structural and functional characteristics of microbial communities from water, rhizosphere and rhizoplane microbial communities associated with three wetland plant species (Iris versicolor, Potamogeton natans and Veronica spicata) at two sites along the Grand River (Ontario Canada) experiencing different levels of anthropogenic impact. West Montrose (WM) is a northern site which has historically been classified as having “good” water quality, while Rare (RA) is a site located in a highly urbanized area receiving effluent from a municipal waste water treatment plant (WWTP). Microbial community composition, assessed using PCR-DGGE, differed between sites, community types and plant species, however, the magnitude of variance between sites was dependent on the associated plant species and the community type. Rhizoplane microbial communities associated with I. versicolor, P. natans, and V. spicata shared 8.1%, 19.9% and 23.9% structural similarity between sites. Rhizosphere microbial communities associated with I. versicolor, P. natans, and V. spicata exhibited 33%, 11.2% and 15.6% structural similarity between sampling locations. Functional community characteristics, determined by BiologTM Ecoplate carbon source utilization profiles exhibited by microbial communities from the rhizoplane and rhizosphere, were unique to each site for I. versicolor and P. natans (rhizoplane community only), but not for V. spicata. Assessment of fecal coliforms and fecal indicator microorganisms (Salmonella, Enterococcus and Escherichia coli) also revealed site-specific differences as well as differences among plant species, most notably the absence of Enterococcus spp. from the rhizosphere of P. natans at both sampling sites. These findings suggest that plant species differ in their ability to recruit root-associated microorganisms, and may be affected differently by variability in environmental conditions, such as site-specific differences in water quality or water chemistry.

Interstitial water microbial communities as an indicator of microbial denitrifying capacity in wood-chip bioreactors

The discharge from food production greenhouses (greenhouse effluent) contains high nutrient and salt concentrations, which, if directly released, can have adverse effects on the environment. Wood-chip bioreactors are increasingly popular passive water treatment systems favoured for their economical denitrification in treating agricultural field tile drainage. Microbial communities are central to denitrification; however little is known about the maturation of microbial communities in wood-chip bioreactors treating greenhouse effluents. In this study, multiple subsurface flow wood-chip bioreactors, each vegetated with a different plant species, together with an unplanted unit, received synthetic greenhouse effluent with elevated nitrate concentrations. The hybrid bioreactors were operated for over 2 years, during which time water samples were collected from the inlet, outlet and within the reactors. The increasing denitrification rate in the bioreactor planted with Typha angustifolia (narrowleaf cattail) correlated with increasing microbial activity and metabolic richness, measured by the carbon utilization patterns in Biolog® EcoPlates. Increased denitrifying gene (nirS) copies (determined by quantitative polymerase chain reaction, qPCR), and near-complete nitrate removal were observed in the T. angustifolia and unplanted reactors after 16 and 23 months of operation respectively. The findings suggested that an acclimation period of at least one year can be expected in unseeded bioreactors planted with T. angustifolia, while bioreactors without vegetation may require a longer time to maximize their denitrification capacity. These results are important for the design and operation of wood-chip bioreactors, which are expected to be more commonly applied in the future.

Microbial diversity and antibiotic resistance in a final effluent-receiving lake

Wastewater treatment plants have been recognised as hotspots for antibiotic resistance genes and antibiotic-resistant bacteria which enter the environment. However, the persistence of these genes and bacteria in receiving ecosystems remains poorly understood. The aim of the study was to evaluate the effect of final effluent release on microbial diversity and the antibiotic resistance gene pool in a final effluent-receiving lake. The numbers of total culturable heterotrophs and unculturable bacteria (represented as the 16S rRNA gene copy number) were significantly reduced during the treatment process. The number of ampicillin-resistant bacteria was higher in the sediment than in water samples, suggesting accumulation of ampicillin-resistant bacteria in freshwater sediments. Using an exogenous method, we captured 56 resistance plasmids which were further characterised. Next-generation sequencing revealed that the microbial phyla represented in the studied metagenomes were typical of corresponding environments. The highest relative abundance of antibiotic resistance genes was observed in the final effluent, suggesting that a considerable number of genes were released from the wastewater treatment plant. However, the lowest relative abundance and lowest diversity of the genes in the lake water, compared to the other studied metagenomes, suggest a negligible effect of treated sewage release on antibiotic resistance within water microbial communities of the lake. Furthermore, uncontrolled sewage dumping into this reservoir in the past as well as lower quality of the water upstream of the lake indicated that the wastewater treatment plant protected the studied ecosystem.

Biotic and abiotic factors influencing channel catfish egg and gut microbiome dynamics during early life stages

This study quantified the effects of pond rearing environments on microbial community composition in larval channel catfish (Ictalurus punctatus) gastrointestinal (GI) tracts across early developmental stages. Larvae were reared under standard industry conditions and sampled at five developmental stages (Egg, Swim-up, Day of stocking, 24 h post-stocking, and 21 d post-stocking). Massive-parallel sequencing of a segment of the 16S rRNA gene was conducted using an Illumina MiSeq platform to characterize the diversity and taxonomic composition of gut and water microbial communities. PERMANOVA analyses of differences in egg and gut microbial community composition across stages indicated a significant interaction between nursery pond environment, and family (P < 0.05) during the last two stages. Proteobacteria and Firmicutes genera along with genera including Vibrio, Aeromonas and Flavobacterium were associated with differences in gut bacterial community composition during larval development before and after pond stocking. Our study demonstrates that the aquatic rearing environment is an important factor influencing the transfer of microbes from water or food into the gut, and provides insight concerning the niche and ecological adaptability of microbes inside the channel catfish gut. Findings demonstrating that catfish gut community composition is highly variable over time indicates probiotic treatments may be possible, however gut community manipulation would require concurrent manipulation of pond or other environmental regimes and microbial communities.

Incorporation of Actinobacillus pleuropneumoniae in Preformed Biofilms by Escherichia coli Isolated From Drinking Water of Swine Farms.

Actinobacillus pleuropneumoniae, the etiological agent of porcine pleuropneumonia, represents one of the most important health problems in the swine industry worldwide and it is included in the porcine respiratory disease complex. One of the bacterial survival strategies is biofilm formation, which are bacterial communities embedded in an extracellular matrix that could be attached to a living or an inert surface. Until recently, A. pleuropneumoniae was considered to be an obligate pathogen. However, recent studies have shown that A. pleuropneumoniae is present in farm drinking water. In this study, the drinking water microbial communities of Aguascalientes (Mexico) swine farms were analyzed, where the most frequent isolated bacterium was Escherichia coli. Biofilm formation was tested in vitro; producing E. coli biofilms under optimal growth conditions; subsequently, A. pleuropneumoniae serotype 1 (strains 4074 and 719) was incorporated to these biofilms. Interaction between both bacteria was evidenced, producing an increase in biofilm formation. Extracellular matrix composition of two-species biofilms was also characterized using fluorescent markers and enzyme treatments. In conclusion, results confirm that A. pleuropneumoniae is capable of integrates into biofilms formed by environmental bacteria, indicative of a possible survival strategy in the environment and a mechanism for disease dispersion.

Detection of microbial disturbances in a drinking water microbial community through continuous acquisition and advanced analysis of flow cytometry data

Detecting disturbances in microbial communities is an important aspect of managing natural and engineered microbial communities. Here, we implemented a custom-built continuous staining device in combination with real-time flow cytometry (RT-FCM) data acquisition, which, combined with advanced FCM fingerprinting methods, presents a powerful new approach to track and quantify disturbances in aquatic microbial communities. Through this new approach we were able to resolve various natural community and single-species microbial contaminations in a flow-through drinking water reactor. Next to conventional FCM metrics, we applied metrics from a recently developed fingerprinting technique in order to gain additional insight into the microbial dynamics during these contamination events. Importantly, we found that multiple community FCM metrics based on different statistical approaches were required to fully characterize all contaminations. Furthermore we found that for accurate cell concentration measurements and accurate inference from the FCM metrics (coefficient of variation ≤ 5%), at least 1000 cells should be measured, which makes the achievable temporal resolution a function of the prevalent bacterial concentration in the system-of-interest. The integrated RT-FCM acquisition and analysis approach presented herein provides a considerable improvement in the temporal resolution by which microbial disturbances can be observed and simultaneously provides a multi-faceted toolset to characterize such disturbances.

The fate of urban springs: Pumping-induced seawater intrusion in a phreatic cave

Sulphur Springs Cave is an extensive phreatic cavity that produces a large, historic spring in the middle of metropolitan Tampa, Florida, USA. The city of Tampa extracts groundwater from the spring to supplement municipal water supply and to support low-salinity habitat in the estuarine Hillsborough River. Extraction at this site has occurred for many decades, but has intensified since the early 2000s, rapidly increasing the salinity of the spring and cave water. The purpose of this study was to address the potential sources and mechanisms of saltwater intrusion at this site using historical and current hydrochemical data published in the literature and online by government agencies. We also explored the cave to identify point-sources of intrusion, and collected water and biological samples from inside the cave to identify potential ecosystem impacts of increasing cave salinity. From 1946 to present, Sulphur Springs water shifted from being fresh (specific conductance <500 µS cm−1) and of calcium-sulfate type to being brackish (specific conductance ∼5000 µS cm−1 and higher) and of sodium-chloride type. We found numerous vents in the cave that issue saline, thermal, sulfidic water and host distinct microbial mat communities. These vents are likely connected to bedrock fractures that provide preferential flow-paths along which confined, deep-sourced saline water enters the freshwater portion of the aquifer, probably originating from the coastal mixing zone. Salinity increased at the spring during dry-season pumping activity and after wet-season recharge events, which likely increased artesian pressure in confined saline aquifer units. Salinization of Sulphur Springs may disrupt the cave microbe and stygobite communities and eventually make the spring unsuitable to maintain low-salinity habitat in the Hillsborough River.

Clay Flocculation Effect on Microbial Community Composition in Water and Sediment

Clay-based flocculation techniques have been developed to mitigate harmful algal blooms; however, the potential ecological impacts on the microbial community are poorly understood. In this study, chemical measurements were combined with 16S rRNA sequencing to characterize the microbial community response to different flocculation techniques, including controls, clay flocculation, clay flocculation with zeolite, and clay flocculation with O2 added zeolite capping. Sediment bacterial biomass measured by PLFA were not significantly altered by the various flocculation techniques used. However, 16S rRNA sequencing revealed differences in water microbial community structure between treatments with and without zeolite capping. The differences were related to significant reductions of total nitrogen (TN), total phosphorus (TP) and ammonia (NH4+) concentration and increase of nitrate (NO3-) concentration in zeolite and O2 loaded zeolite capping. The relative abundance of ammonia oxidizing bacteria increased fourfold in zeolite capping microcosms, suggesting zeolite promoted absorbed ammonia removal in the benthic zone. Zeolite-capping promoted bacteria nitrogen cycling activities at the water-sediment interface. Potential pathogens that are usually adapted to eutrophic water bodies were reduced after clay flocculation. This study demonstrated clay flocculation did not decrease bacterial populations overall and may reduce regulatory indicators and pathogenic contaminants in water. Zeolite capping may also help prevent nutrients from being released back into the water thus preventing additional algal blooms.

Microbial Community Composition and Putative Biogeochemical Functions in the Sediment and Water of Tropical Granite Quarry Lakes.

Re-naturalized quarry lakes are important ecosystems, which support complex communities of flora and fauna. Microorganisms associated with sediment and water form the lowest trophic level in these ecosystems and drive biogeochemical cycles. A direct comparison of microbial taxa in water and sediment microbial communities is lacking, which limits our understanding of the dominant functions that are carried out by the water and sediment microbial communities in quarry lakes. In this study, using the 16S rDNA amplicon sequencing approach, we compared microbial communities in the water and sediment in two re-naturalized quarry lakes in Singapore and elucidated putative functions of the sediment and water microbial communities in driving major biogeochemical processes. The richness and diversity of microbial communities in sediments of the quarry lakes were higher than those in the water. The composition of the microbial communities in the sediments from the two quarries was highly similar to one another, while those in the water differed greatly. Although the microbial communities of the sediment and water samples shared some common members, a large number of microbial taxa (at the phylum and genus levels) were prevalent either in sediment or water alone. Our results provide valuable insights into the prevalent biogeochemical processes carried out by water and sediment microbial communities in tropical granite quarry lakes, highlighting distinct microbial processes in water and sediment that contribute to the natural purification of the resident water.

Soils act as sinks or sources of CH4 depending on air-filled porosity in sclerophyllous ecosystems in semiarid central Chile

Carbon dioxide (CO2) and methane (CH4) are greenhouse gases (GHG), which sustained increase in the atmosphere contribute to global warming and climate change. The GHG fluxes of soils are strongly controlled by water content, temperature, plant and microbial communities and soil management. The Chilean sclerophyllous ecosystem is a global biodiversity hotspot historically and increasingly threatened by human activity. The aim of this study was to compare soil CH4 (and CO2) fluxes, under prevailing aerobic (dry hot summer) versus presumed partial anaerobic (wet winter) conditions, across a disturbance gradient in sclerophyllous ecosystems of central semiarid Chile. The CO2 fluxes were measured with an infrared gas analyzer (IRGA) while CH4 fluxes by gas chromatography using closed soil chambers. Soils were sources of CO2 (∼3.35 µmol CO2 m−2 s−1) drastically changing with vegetation and seasons. Soils were generally sinks of CH4 in summer (∼−3.75 nmol CH4 m−2 s−1) and sources in winter (∼+4.12 nmol CH4 m−2 s−1), which was mainly explained by air filled porosity. Modelled values showed that soils of the severely-disturbed A. caven savannah was overall a CH4 source (0.86 g CH4 m−2 year−1), while the strongly-disturbed thorn scrub (−0.56 g CH4 m−2 year−1) and the moderately-disturbed sclerophyllous forest (−2.68 g CH4 m−2 year−1) were sinks. Hence protecting sclerophyllous forests and restoring disturbed ecosystems may contribute to mitigate anthropogenic CH4 emissions.

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.