Solid State Phenomena Vol. 262

Abstract: Bioleaching is the extraction of metals from ore by microorganisms. Initial attachment and formation of biofilm by microorganisms are very important for the bioleaching due to the mineral oxidation processes. However, very few techniques were proposed to monitor initial stage of biofilms in real time. Therefore, the aim of this work was to probe an electrochemical method on the bacterial biofilm model under the laboratory conditions. It was found that electrochemical method can be suggested for the real time detection of initial phase of P. polymyxa biofilm formation by observation of the potential increase. However, detection of biofilm development at late stages was not successful due to the decrease of the electrochemical potential by full coverage of the test surface. Nevertheless, this technique is supposed as a promising method for early stage detection of desirable biofilms of acidophilic iron oxidizing microorganisms in bioleaching.

Abstract: In this work, we present an Electrochemical Impedance Spectroscopy (EIS) study using a carbon paste electrode modified with chalcopyrite (CuFeS₂) containing 50 wt% of the mineral (particle size < 38 μm) and graphite (particle size < 20 μm) in naturally aerated salt acid solutions (pH 1.8) without and with the addition of 0.100 mol L^-1 of ferrous ions. The aim was to evaluate the influence of the solution potential on the behavior of chalcopyrite electrode in the presence and absence of iron (II) ions. Additionally, we evaluated the influence of the bacteria Acidithiobacillus ferrooxidans in the system containing iron (II) ions without applying potential. Therefore, EIS was used to investigate the processes occurring at the electrode/solution interface in the different systems, considering the charge transfer reactions involving chalcopyrite and ferrous ions, the presence of a multicomponent layer, and diffusion. The results showed that the combination of iron (II) ions with the imposition of low potential values (0.100 Fe²⁺ ions with +0.300 V/Ag|AgCl|KCl_3mol/L) activates the chalcopyrite surface and enhances the copper recovery.

Abstract: Siderophores are produced by microorganisms in iron-deficient environments. They are classified by structure as hydroxamate, catecholate, carboxylate or mixed type siderophores. These differences are also reflected in the selectivity for other valuable elements than iron, which allows designating them as “metallophores”, and makes them of interest for several industrial and medical applications. Thus, it is essential to understand the biosynthesis of these molecules to increase the set of available metallophores that are stable and suited for the respective applications. The probable structure of the metallophore from T. agreste DSM 44070 was predicted by similarity search and gene annotation. An N-hydroxylating monooxygenase (NMO: TheA) of T. agreste DSM 44070 that catalyzes an initial step was synthesized and characterized in detail. The respective metallophore was synthesized, purified and studied. The structure prediction suggested a hydroxamate-type (Erythrochelin-like) metallophore that contains _L-N5-hydroxyornithine. This precursor is synthesized by TheA. The siderophore designated as “Thermochelin” is produced, extracted and purified successfully. Complexation was confirmed by CAS-assay. In this study, we expanded the scope of siderophores and the knowledge towards their biosynthetic pathways. Thermochelin is the second siderophore, which was purified from a thermophilic organism, and TheA is the first NMO, which was characterized from an extremophile.

Abstract: Siderophores are low-molecular weight compounds that are produced by organisms to assimilate vital Fe³⁺ out of iron-deficient environments. They are of interest for several (bio-) technological applications because of their high selectivity for several metal ions. Unfortunately, the concentration in supernatants is often low and thus it is challenging to purify or even enrich these compounds. We applied different types of siderophores onto an immobilized metal-resin that was loaded with either Ni²⁺, Co²⁺ or Fe³⁺. Elution was done with ethanol to reduce salt load and facilitate downstream processing. Thus, it is possible to enrich as well as desalt a sample within one-step from culture supernatant, which allows faster characterization and application of siderophores.

Abstract: Siderophores play an important role in the solubilisation and mobilization of iron (III) and various metal ions. To have a useful method to test siderophores in culture supernatants for their metal binding affinity, we redesigned and optimized the liquid CAS-assay for selected metal ions. CAS-assay solutions were calibrated with desferrioxamine B in different concentrations to calculate DFOB-equivalents to get a semi-quantitative evaluation. With these assay solutions, we were able to test siderophores in culture supernatants for their ability to chelate with Fe, Al, Ga, Cu, V and As.

Abstract: In the present study we explore the idea of biotechnologically produced metallophore mixtures as selective chelating compounds for economically valuable metals from various sources. A complex soil matrix with natural levels of metal mineralization was employed as a potential source of metals. We focused on gallium-chelating metallophore preparations of two soil bacteria (Gordonia rubripertincta CWB2 and Paracoccus denitrificans PD1222) which were compared to the commercially available desferrioxamine B (DFOB). As a reference, the binding of iron was analyzed. The herein described successful mobilization of metals such as gallium from soil provides first hints towards alternative strategies, such as phytomining, sensor development, or solvent extraction based on metallophores. The metallophore mixture produced by the strains showed best results at pH 8 and allowed to mobilize gallium about three times better as the pure commercially available DFOB.

Abstract: Gordonia rubripertincta CWB2 produces hydroxamate-type siderophores. Therefore it was cultivated under iron limitation. Analytical reversed-phase HPLC allowed determining a single peak of ferric iron chelating compounds from culture broth. The elution profile and its absorbance spectrum were similar to those of desferrioxamine B. The latter is a commercial available metal chelating agent which is of interest for industries. We successfully developed an HPLC protocol to separate metal-free and metal-loaded desferrioxamines. Further, we aimed to increase the re-usability of desferrioxamines as metal chelators by immobilization on silica based carriers. The siderophores of strain CWB2 have been covalently linked to the carrier with a high yield (up to 95%). Metal binding studies demonstrated that metals can be bound to non-immobilized as well as to the covalently linked desferrioxamines.

Abstract: Detailed descriptions of the consortia present in commercial mineral processing operations have emerged in recent years, improving our understanding of the biology and the ecology of bioleaching. In spite of this progress, one of the aspects of biomining microbial ecology that remains un-tackled is that of virus-host interactions. The effects of viruses on the dynamics of the bioleaching microbial consortia and their impact in metal recovery is presently unknown. To begin addressing this issue we asked a basic question: ¿Are there viruses in industrial bioleaching econiches In this work, we answer that question experimentally, assessing the number and types of viral particles recovered in the leachates from different industrial settings, using epifluorescence and transmission electron microscopy. Findings emerging from this work point to an almost null presence of viral particles in the leachates from mineral processing operations, possibly due to structural stability issues of the particles in the extreme acidic and highly oxidant conditions favoured by their potential microbial hosts. In turn, DNA-loaded viral-size vesicles of presently unknown function are frequent and abundant in all samples analysed.

Abstract: Relatively little is known about the microbial communities present in natural environments that meet physico-chemical conditions for the development of potential leaching microorganisms such as thermal ecosystems from the Chilean Altiplano. Thermophilic leaching enrichments were obtained and identified from a high altitude solfataric pound in Lirima hot springs in the Chilean Altiplano. This ecosystem is characterized by hot underground freshwaters, enriched in sulfur compounds showing pH from neutral to acidic. Microbial diversity has been scarcely explored here, and preliminary results demonstrate that hydrothermal pounds are represented by thermophilic anaerobic and acidophilic taxa. Thermophilic leaching cultures in shake flasks were obtained using ferrous iron and pyrite as energy source. The presence of Bacteria and Archaea in oxidizing enrichments was determined by PCR amplification of 16S rRNA genes. A preliminary analysis of microbial diversity using massive sequencing revealed that Bacteria were more abundant than Archaea in both enrichments. Specifically for the iron-oxidizing culture, the majority of the sequences clustered within the Proteobacteria phylum (79%). Among Proteobacteria, the proportion of Betaproteobacteria (42.2%) and Gammaproteobacteria (21.27%) was much higher than that of Alphaproteobacteria (15.5%). Within the Betaproteobacteria class, the most frequent genus was Leptothrix-like. Similar results were obtained for the pyrite oxidizing culture. Interestingly, this study shows the presence of microorganisms close to the Leptothrix genus under low pH conditions (1.7-2.8) and their capacity to grow at high temperatures with ferrous iron or pyrite as sole energy source

Abstract: The diversity of microbial community is well studied in past decades, however, the functional gene diversity in AMD and sediment are still unclear. In this study, four samples, which included two mine drainages and two sediments were taken from two typical copper mines in the southeast of China. Community DNA from the AMD and corresponding sediments were were extracted, purified, amplified, labeled and hybridized with GeoChip 2.0. The results showed that total 28, 126, 1131, 1875 functional genes were detected in DX_110, YP_NK, DX_110N, YP_NKN, respectively, which including carbon and nitrogen fixation, carbon degradation, methane metabolism, ammonification, nitrification, denitrification, nitrogen reduction, sulfur reduction and metal resistance genes. Sediment nearby the mine drainage may play an important role in microbial geochemical processes, since more functional genes and higher diversity were detected in sediment than in AMD.