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
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.