Association of Acidotolerant Cyanobacteria to Microbial Mats below pH 1 in Acidic Mineral Precipitates in Río Tinto River in Spain.

This report describes acidic microbial mats containing cyanobacteria that are strongly associated to precipitated minerals in the source area of Río Tinto. Río Tinto (Huelva, Southwestern Spain) is an extreme acidic environment where iron and sulfur cycles play a fundamental role in sustaining the extremely low pH and the high concentration of heavy metals, while maintaining a high level of microbial diversity. These multi-layered mineral deposits are stable all year round and are characterized by a succession of thick greenish-blue and brownish layers mainly composed of natrojarosite. The temperature and absorbance above and below the mineral precipitates were followed and stable conditions were detected inside the mineral precipitates. Different methodologies, scanning and transmission electron microscopy, immunological detection, fluorescence in situ hybridization, and metagenomic analysis were used to describe the biodiversity existing in these microbial mats, demonstrating, for the first time, the existence of acid-tolerant cyanobacteria in a hyperacidic environment of below pH 1. Up to 0.46% of the classified sequences belong to cyanobacterial microorganisms, and 1.47% of the aligned DNA reads belong to the Cyanobacteria clade.

Adaptation of granular sludge microbial communities to nitrate, sulfide, and/or p-cresol removal

Effluents from petroleum refineries contain a toxic mixture of sulfide, nitrogen, and phenolic compounds that require adequate treatment for their removal. Biological denitrification processes are a cost-effective option for the treatment of these effluents, but the knowledge on the microbial interactions in simultaneous sulfide and phenol oxidation in denitrifying reactors is still very limited. In this work, microbial community structure and macrostructure of granular biomass were studied in three denitrifying reactors treating a mixture of inorganic (sulfide) and organic (p-cresol) electron donors for their simultaneous removal. The differences in the available substrates resulted in different community assemblies that supported high removal efficiencies, indicating the community adaptation capacity to the fluctuating compositions of industrial effluents. The three reactors were dominated by nitrate reducing and denitrifying bacteria where Thiobacillus spp. were the prevalent denitrifying organisms. The toxicity and lack of adequate substrates caused the endogenous decay of the biomass, leading to release of organic matter that maintained a diverse although not very abundant group of heterotrophs. The endogenous digestion of the granules caused the degradation of its macrostructure, which should be considered to further develop the denitrification process in sulfur-based granular reactors for treatment of industrial wastewater with toxic compounds

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Comparative microbial ecology of the water column of an extreme acidic pit lake, Nuestra Señora del Carmen, and the Río Tinto basin (Iberian Pyrite Belt)

The Iberian Pyrite Belt, located in Southwestern Spain, represents one of the world’s largest accumulations of mine wastes and acid mine drainages. This study reports the comparative microbial ecology of the water column of Nuestra Señora del Carmen acid pit lake with the extreme acidic Río Tinto basin. The canonical correspondence analysis identified members of the Leptospirillum, Acidiphilium, Metallibacterium, Acidithiobacillus, Ferrimicrobium and Acidisphaera genera as the most representative microorganisms of both ecosystems. The presence of archaeal members is scarce in both systems. Only sequences clustering with the Thermoplasmata have been retrieved in the bottom layer of Nuestra Señora del Carmen and one station of Río Tinto. Although the photosynthetically active radiation values measured in this lake upper layer were low, they were sufficient to activate photosynthesis in acidophilic microorganisms. All identified photosynthetic microorganisms in Nuestra Señora del Carmen (members of the Chlamydomonas, Zygnemopsis and Klebsormidium genera) are major members of the photosynthetic eukaryotic community characterized in Río Tinto basin. This study demonstrates a close relationship between the microbial diversity of Nuestra Señora del Carmen pit lake and the diversity detected in the Río Tinto basin, which underlain the influence of the shared mineral substrates in the microbial ecology of these ecosystems (AU)

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Electricity generation by microorganisms in the sediment-water interface of an extreme acidic microcosm

The attachment of microorganisms to electrodes is of great interest for electricity generation in microbial fuel cells (MFC) or other applications in bioelectrochemical systems (BES). In this work, a microcosm of the acidic ecosystem of Río Tinto was built and graphite electrodes were introduced at different points. This allowed the study of electricity generation in the sediment/water interface and the involvement of acidophilic microorganisms as biocatalysts of the anodic and cathodic reactions in a fuel-cell configuration. Current densities and power outputs of up to 3.5 A/m2 and 0.3 W/m2, respectively, were measured at pH 3. Microbial analyses of the electrode surfaces showed that Acidiphilium spp., which uses organic compounds as electron donors, were the predominant biocatalysts of the anodic reactions, whereas the aerobic iron oxidizers Acidithiobacillus ferrooxidans and Leptospirillum spp. were detected mainly on the cathode surface (AU)

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Microbial community composition of anoxic marine sediments in the Bay of Cádiz (Spain)

The composition of the microbial community inhabiting the anoxic coastal sediments of the Bay of Cádiz (southern Spain) was investigated using a molecular approach consisting of PCR cloning and denaturing gradient gel electrophoresis (DGGE), based on 16S rRNA sequences. The total cell count was 1-5 × 10⁸ cells/g sediment and, as determined by catalyzed reporter deposition-fluorescent in situ hybridization (CARD-FISH), the proportion of Bacteria to Archaea was about 70:30. The analysis of 16S-rRNA gene sequences revealed a wide spectrum of microorganisms, which could be grouped into 111 operational taxonomic units (OTUs). Many of the OTUs showed high phylogenetic similarity to microorganisms living in marine sediments of diverse geographic origin. The phylogenetic groups that were predominantly detected were Firmicutes, Deltaproteobacteria, and Gammaproteobacteria, accounting for 23, 15, and 14% of the clones, respectively. Diversity in the domain Archaea was significantly lower than in the domain Bacteria. The majority of the archaeal OTUs belonged to the Crenarchaeota phylum. Since most of the sequences could not be identified precisely at the genus/species level, the functional roles of the microorganisms in the ecosystem could not be inferred. However, seven OTUs affiliated with the Delta- and Epsilonproteobacteria were identified down to the genus level, with all of the identified genera known to occur in sulfate-rich marine environments (AU)

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Eukaryotic microbial diversity of phototrophic microbial mats in two Icelandic geothermalhot springs

The composition of the eukaryotic community and the three-dimensional structure of diverse phototrophic microbial mats from two hot springs in Iceland (Seltun and Hveradalir geothermal areas) were explored by comparing eukaryotic assemblages from microbial mats. Samples were collected in July 2007 from 15 sampling stations along thermal and pH gradients following both hot springs. Physicochemical data revealed high variability in terms of pH (ranging from 2.8 to 7), with high concentrations of heavy metals, including up to 20 g Fe/l, 80 mg Zn/l, 117 mg Cu/l, and 39 mg Ni/l at the most acidic sampling points. Phylogenetic analysis of 18S rDNA genes revealed a diversity of sequences related to several taxa, including members of the Bacillariophyta, Chlorophyta, Rhodophyta, and Euglenophyta phyla as well as ciliates, amoebae, and stramenopiles. The closest relatives to some of the sequences detected came from acidophilic organisms, even when the samples were collected at circumneutral water locations. Electron microscopy showed that most of the microecosystems analyzed were organized as phototrophic microbial mats in which filamentous cyanobacteria usually appeared as a major component. Deposits of amorphous minerals rich in silica, iron, and aluminium around the filaments were frequently detected (AU)

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Assessment of the addition of Thiobacillus denitrificans and Thiomicrospira denitrificans to chemolithoautotrophic denitrifying bioreactors

The aim of the present study was to assess the impact of adding cultures of Thiobacillus denitrificans and Thiomicrospira denitrificans to two upflow anaerobic sludge bed (UASB) reactors: one inoculated with granular sludge and the other filled only with activated carbon (AC). The performances of the bioreactors and the changes in biomass were compared with a non-bioaugmented control UASB reactor inoculated with granular sludge. The reactors inoculated with granular sludge achieved efficiencies close to 90% in nitrate and thiosulfate removal for loading rates as high as 107 mmol-NO3 -/l per day and 68 mmol-S2O3 2-/l per day. Bioaugmentation with Tb. denitrificans and Tm. denitrificans did not enhance the efficiency compared to that achieved with non-bioaugmented granular sludge. The loading rates and efficiencies were 30-40% lower in the AC reactor. In all the reactors tested, Tb. denitrificans became the predominant species. The results strongly suggest that this bacterium was responsible for denitrification and sulfoxidation within the reactors. We additionally observed that granules partially lost their integrity during operation under chemolithoautotrophic conditions, suggesting limitations for long-term operation if bioaugmentation is applied in practice (AU)

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Prokaryotic community structure in algal photosynthetic biofilms from extreme acidic streams in Río Tinto (Huelva, Spain)

Four algal photosynthetic biofilms were collected from the Río Tinto (SW Spain) at four localities: AG, Euglena and Pinnularia biofilms; ANG, Chlorella and Pinnularia biofilms; RI, Cyanidium and Dunaliella biofilms; and CEM, Cyanidium, Euglena and Pinnularia biofilms. Community composition and structure were studied by a polyphasic approach consisting of 16S rRNA analysis, scanning electron microscopy by back-scattered electron detection mode (SEM-BSE), and fluorescence in-situ hybridization (FISH). Acidophilic prokaryotes associated with algal photosynthetic biofilms included sequences related to the Alpha-, Beta-, and Gammaproteobacteria (phylum Proteobacteria) and to the phyla Nitrospira, Actinobacteria, Acidobacteria and Firmicutes. Sequences from the Archaea domain were also identified. No more than seven distinct lineages were detected in any biofilm, except for those from RI, which contained fewer groups of Bacteria. Prokaryotic communities of the thinnest algal photosynthetic biofilms (-100 microm) were more related to those in the water column, including Leptospirillum populations. In general, thick biofilms (200 microm) generate microniches that could facilitate the development of less-adapted microorganisms (coming from the surrounding environment) to extreme conditions, thus resulting in a more diverse prokaryotic biofilm (AU)

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Purification and biological characterization of halocin H1 from Haloferax mediterranei M2a

The production of halocins, bacteriocin-like proteins of ecological significance, is a frequent characteristic of species from the family Halobacteriaceae. Halocin H1, produced by Haloferax mediterranei strain M2a, is a single 31-kDa polypeptide. Its purification was achieved by combining two chromatographic systems: Sepharose 4B linked to bacitracin followed by hydroxylapatite Bio-gel HTP. Halocin H1 required concentrations of NaCl higher than 1.5 M to maintain its activity. Haoarchaeal strains showed a differential degree of sensitivity to the action of this halocin (AU)

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