Comparative genomics begins to unravel the ecophysiology of bioleaching

A comparison of the metabolic potential of 20 bioleaching microorganisms and their close relatives from the Eubacteria and Archaea kingdoms permits the prediction of inter-and intra-species physiological interactions (ecophysiology) during spatial and temporal changes that are known to occur within industrial bioleaching heaps. Genome analysis has allowed preliminary models to be built for genes and pathways involved in key processes such as nitrogen and carbon cycling, sulfur and iron uptake and homeostasis, extra-cellular polysaccharide biosynthesis, heavy metal resistance and energy metabolism. This paper will focus on the diverse ways that bioleaching microorganisms obtain carbon from their environment with a particular emphasis on elucidating how these processes might be expected to vary over space and time during the lifetime of a bioleaching operation. It is anticipated that this knowledge will improve our understanding of fundamental biological processes in extremely acidic environments

A method for evaluating the proportion of free and attached bacteria in the bioleaching of chalcopyrite with Thiobacillus ferrooxidans

A method for evaluating the proportion of bacteria attached to mineral sulfides is presented. The method is based on the determination of the rate of ferrous iron oxidation by attached bacteria on the mineral surfaces. The values obtained with this procedure are in agreement with measurements of attached bacteria using bacteria grown with radioactive (C14) NaHCO3. The methodology was used to evaluate the fraction of bacteria attached to chalcopyrite during bioleaching of this sulfide. It was observed that a significant fraction of the bacteria grow attached to the mineral

Bacterial populations in samples of bioleached copper ore as revealed by analysis of DNA obtained before and after cultivation.

The composition of bacterial populations in copper bioleaching systems was investigated by analysis of DNA obtained either directly from ores or leaching solutions or after laboratory cultures. This analysis consisted of the characterization of the spacer regions between the 16 and 23S genes in the bacterial rRNA genetic loci after PCR amplification. The sizes of the spacer regions, amplified from DNAs obtained from samples, were compared with the sizes of those obtained from cultures of the main bacterial species isolated from bioleaching systems. This allowed a preliminary assessment of the bacterial species present in the samples. Identification of the bacteria was achieved by partial sequencing of the 16S rRNA genes adjacent to the spacer regions. The spacer regions observed in DNA from columns leached at different iron concentrations indicated the presence of a mixture of different bacteria. The spacer region corresponding to Thiobacillus ferrooxidans was the main product observed at high ferrous iron concentration. At low ferrous iron concentration, spacer regions of different lengths, corresponding to Thiobacillus thiooxidans and "Leptospirillum ferrooxidans" were observed. However, T. ferrooxidans appeared to predominate after culture of these samples in medium containing ferrous iron as energy source. Although some of these strains contained singular spacer regions, they belonged within previously described groups of T. ferrooxidans according to the nucleotide sequence of the neighbor 16S rRNA. These results illustrate the bacterial diversity in bioleaching systems and the selective pressure generated by different growth conditions

Isolation and nucleotide sequence of the Thiobacillus ferrooxidans genes for the small and large subunits of ribulose 1,5-bisphosphate carboxylase/oxygenase

AbstractThe genes encoding for the large (rbcL) and small (rbcS) subunits of ribulose-1,5-bisphosphate car☐ylase (RuBisCO) were cloned from the obligate autotrophThiobacillus ferrooxidans, a bacterium involved in the bioleaching of minerals. Nucleotide sequence analysis of the cloned DNA showed that the two coding regions are separated by a 30-bp intergenic region, the smallest described for the RuBisCO genes. TherbcL andrbcS genes encode polypeptides of 473 and 118 amino acids, respectively. Comparison of the nucleotide and amino acid sequences with those of the genes forrbcL andrbcS found in other species demonstrated that theT. ferrooxidans genes have the closest degree of identity with those ofChromatium vinosum and ofAlvinoconcha hessleri endosymbiont. BothT. ferrooxidans enzyme subunits contain all the conserved amino acids that are known to participate in the catalytic process or in holoenzyme assembly

Subjetividades y saberes docentes en el sistema educativo chileno: un análisis desde las concepciones de formadores de profesores

El presente estudio analiza las concepciones que los formadores de profesores poseen sobre las subjetividades y saberes de los docentes del sistema escolar chileno. El diseño de investigación consideró la aplicación de entrevistas en profundidad a nueve formadores de profesores de una universidad estatal. La información resultante fue procesada utilizando la Grounded Theory. Los resultados relevan las concepciones de los formadores de profesores respecto del valor pedagógico del saber y la subjetividad docente. Estas concepciones se discuten con la investigación internacional. Se concluye enfatizando la necesidad de dotar de especificidad al trabajo docente de tal manera de aportar insumos para la transformación de la formación docente

Sulfatides are required for renal adaptation to chronic metabolic acidosis

Urinary ammonium excretion by the kidney is essential for renal excretion of sufficient amounts of protons and to maintain stable blood pH. Ammonium secretion by the collecting duct epithelia accounts for the majority of urinary ammonium; it is driven by an interstitium-to-lumen NH3 gradient due to the accumulation of ammonium in the medullary and papillary interstitium. Here, we demonstrate that sulfatides, highly charged anionic glycosphingolipids, are important for maintaining high papillary ammonium concentration and increased urinary acid elimination during metabolic acidosis. We disrupted sulfatide synthesis by a genetic approach along the entire renal tubule. Renal sulfatide-deficient mice had lower urinary pH accompanied by lower ammonium excretion. Upon acid diet, they showed impaired ammonuria, decreased ammonium accumulation in the papilla, and chronic hyperchloremic metabolic acidosis. Expression levels of ammoniagenic enzymes and Na(+)-K(+)/NH4(+)-2Cl(-) cotransporter 2 were higher, and transepithelial NH3 transport, examined by in vitro microperfusion of cortical and outer medullary collecting ducts, was unaffected in mutant mice. We therefore suggest that sulfatides act as counterions for interstitial ammonium facilitating its retention in the papilla. This study points to a seminal role of sulfatides in renal ammonium handling, urinary acidification, and acid-base homeostasis