The Tinto River is an extreme environment located at the core of the Iberian Pyritic Belt (IPB). It is an unusual ecosystem due to its size (100 km long), constant acidic pH (mean pH, 2.3), and high concentration of heavy metals, iron, and sulfate in its waters, characteristics that make the Tinto River Basin comparable to acidic mine drainage (AMD) systems. In this paper we present an extensive survey of the Tinto River sediment microbiota using two culture-independent approaches: denaturing gradient gel electrophoresis and cloning of 16S rRNA genes. The taxonomic affiliation of the Bacteria showed a high degree of biodiversity, falling into 5 different phyla: Proteobacteria , Firmicutes , Bacteroidetes , Acidobacteria , and Actinobacteria ; meanwhile, all the Archaea were affiliated with the order Thermoplasmatales . Microorganisms involved in the iron ( Acidithiobacillus ferrooxidans , Sulfobacillus spp., Ferroplasma spp., etc.), sulfur ( Desulfurella spp., Desulfosporosinus spp., Thermodesulfobium spp., etc.), and carbon ( Acidiphilium spp., Bacillus spp., Clostridium spp., Acidobacterium spp., etc.) cycles were identified, and their distribution was correlated with physicochemical parameters of the sediments. Ferric iron was the main electron acceptor for the oxidation of organic matter in the most acid and oxidizing layers, so acidophilic facultative Fe(III)-reducing bacteria appeared widely in the clone libraries. With increasing pH, the solubility of iron decreases and sulfate-reducing bacteria become dominant, with the ecological role of methanogens being insignificant. Considering the identified microorganisms—which, according to the rarefaction curves and Good's coverage values, cover almost all of the diversity—and their corresponding metabolism, we suggest a model of the iron, sulfur, and organic matter cycles in AMD-related sediments.

Methanogenic granules from an anaerobic bioreactor that treated wastewater of a beer brewery consisted of different morphological types of granules. In this study, the microbial compositions of the different granules were analyzed by molecular microbiological techniques: cloning, denaturing gradient gel electrophoresis and fluorescent in situ hybridization (FISH), and scanning and transmission electron microscopy. We propose here that the different types of granules reflect the different stages in the life cycle of granules. Young granules were small, black, and compact and harbored active cells. Gray granules were the most abundant granules. These granules have a multilayer structure with channels and void areas. The core was composed of dead or starving cells with low activity. The brown granules, which were the largest granules, showed a loose and amorphous structure with big channels that resulted in fractured zones and corresponded to the older granules.Firmicutes(as determined by FISH) andNitrospiraandDeferribacteres(as determined by cloning and sequencing) were the predominantBacteria. Remarkably,Firmicutescould not be detected in the brown granules. The methanogenicArchaeaidentified wereMethanosaeta concilii(70 to 90% by FISH and cloning),Methanosarcina mazei, andMethanospirillumspp. The phenotypic appearance of the granules reflected the physiological condition of the granules. This may be valuable to easily select appropriate seed sludges to start up other reactors.