Advanced Materials Research Vols. 20-21

Abstract: Acidithiobacillus ferrooxidans, an acidophilic, chemolithotrophic, γ-proteobacterium, is involved in the bioleaching of metal sulfides. For this process, bacterial attachment to mineral surface and biofilm development play a pivotal role. Generally, biofilm formation and production of exopolysaccharides is regulated by the second messenger cyclic diguanylic acid (c-di-GMP) whose cellular level depends on the synthesis and degradation activities of diguanylate cyclase (DGCs, with GGDEF domain) and phosphodiesterase (PDE, with EAL or HD-GYP domains), respectively. The analysis of the genomic sequence of A. ferrooxidans ATCC 23270 allowed us to identify 5 putative orfs encoding DGC and/or PDE-like proteins. Four of them encode for bifunctional putative proteins with GGDEF and EAL domains and are named AFE_0053, AFE_1360, AFE_1373 and AFE_1379. The fifth one named AFE_1852 has an EAL domain. The putative proteins also include PAS and GAF domains involved in signal transduction. These features suggest an involvement in signalling transduction through the metabolism of c-di-GMP. The amino acid sequences of these putative proteins were aligned with known DGCs and PDEs. Alignments indicate that AFE_1360 and AFE_1373 share more consensus sequences with active PDEs, whereas AFE_0053 and AFE_1379 do with active DGCs. On the other hand, in AFE_1852 some conserved residues of known active PDEs are changed. RT-PCR-experiments revealed that the genes that encode for these putative DGCs and/or PDEs are expressed by growth on two different substrates. These preliminary results suggest that A. ferrooxidans possesses a c-di-GMP pathway that should be involved in biofilm formation, as it occurs in many bacteria.

Abstract: Bioleaching studies have been conducted to obtain bacteria having a high ability to dissolve copper from chalcopyrite. For these studies, samples of mine drainage water which contain high concentrations of copper or iron ions in several abandoned mines in Japan were used to inoculate enrichment cultures on 0.16 M ferrous iron in the absence of chalcopyrite concentrate. Afterwards, these were accumulated and supplied to shaking-flask bioleaching tests on chalcopyrite concentrate. Copper dissolution rates were measured in chalcopyrite leaching experiments and compared with those using cell-free ferrous/ferric media. The copper dissolution rate in ferrous sulphate medium was higher than that in ferric sulphate medium. Moreover, tests in the presence of bacteria showed even an higher copper dissolution rate.

Abstract: A comparative study on the Fe-reducing ability of pure anaerobic strains of Geobacter metallireducens and Bacillus infernus was investigated using different sources of Fe(III). Batch tests were carried out in aqueous solutions containing a reducing agent (lactate or formate) and at a constant temperature of 37°C and 50°C respectively. The formation of biogenic compounds of Fe(II) was determined using XRD and SEM-EDX techniques. The bioreduction of magnetite was not affected by the type of bacterial strain used. The kinetics of the process, initially very fast, stopped rapidly for both types of microorganisms. Vivianite (Fe3(PO4)2.8H2O) was detected as the main biogenic compound formed during the bioreduction process.

Abstract: Catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH) is a powerful method with a growing number of applications in the quantitative evaluation of microbial populations of complex ecosystems. CARD-FISH is an improvement over traditional fluorescence in situ hybridization (FISH) especially suitable for aquatic habitats with small, slow growing, or starving bacteria, in which the signal intensities of hybridized cells is frequently below detection limits or lost in high fluorescence background of dense mineral matrixes. In this work we report the development of protocols and probes for the identification and quantification of the microorganisms involved in the continuous bioleaching of a cobaltiferrous concentrate using a four tank-leaching reactor operated by BRGM. After steady state was reached, samples were taken to identify and quantify the microorganisms present in the each of the tanks used in the process.