Cecilia Bernardelli

EXAFS and DFT study of the cadmium and lead adsorption on modified silica nanoparticles

Silica nanoparticles of 7 nm diameter were modified with (3-aminopropyl) triethoxysilane (APTES) and characterized by CP-MAS (13)C and (29)Si NMR, FTIR, zeta potential measurements, and thermogravimetry. The particles were shown to sorb successfully divalent lead and cadmium ions from aqueous solution. Lead complexation with these silica nanoparticles was clearly confirmed by EXAFS (Extended X-ray Absorption Fine Structure) with synchrotron light measurements. Predicted Pb-N and Pb-C distances obtained from quantum-chemical calculations are in very good agreement with the EXAFS determinations. The calculations also support the higher APTES affinity for Pb(2+) compared to Cd(2+).

Symbiotic phenotype of a membrane-bound glucose dehydrogenase mutant of Sinorhizobium meliloti

We have previously reported detection of significant pyrroloquinoline quinone-linked glucose dehydrogenase activity in Sinorhizobium meliloti cells isolated from alfalfa (Medicago sativa L.) nodules. In this work, we report the expression of the gcd gene (SMc00110) during root nodule development and characterize the symbiotic phenotype of S. meliloti gcd mutant RmH580. Using a S. meliloti strain carrying a gcd–lacZ transcriptional fusion, gcd expression was detected from very early stages of plant–bacteria interactions, at the rhizosphere level, and during further stages of nodule development. Alfalfa plants inoculated with RmH580 showed a delay in nodule emergence and a reduced ability for nodulation at various inoculum dosages. RmH580 was also deficient in its competitive ability; in coinoculation experiments a mutant:wild-type inoculum ratio higher than 100:1 was necessary to obtain an equal ratio of nodule occupancy. These results indicate that PQQ-linked glucose dehydrogenase is required by S. meliloti for optimal nodulation efficiency and competitiveness on alfalfa roots.

Energy Generation by Extracellular Aldose Oxidation in N2-Fixing Gluconacetobacter diazotrophicus

ABSTRACT Gluconacetobacter diazotrophicus PAL3 was grown in a chemostat with N2 and mixtures of xylose and gluconate. Xylose was oxidized to xylonate, which was accumulated in the culture supernatants. Biomass yields and carbon from gluconate incorporated into biomass increased with the rate of xylose oxidation. By using metabolic balances it is demonstrated that extracellular xylose oxidation led N2-fixing G. diazotrophicus cultures to increase the efficiency of energy generation.

Recovery of Zinc during the Pre-Treatment of a Refractory Gold-Bearing Ore

Mesophilic bacteria were enriched from samples collected from acid mine drainages in La Carolina (San Luis, Argentina). Two enrichments, E1 and E2, showed suitable rates for iron or sulphur oxidation, respectively. Both enrichments were characterized by FISH analysis. They were mainly composed by Leptospirillum ferrooxidans and Acidithiobacillus ferrooxidans respectively. Studies with both, mixed and individual enrichments, showed biooxidation (measured as iron solubilisation) of a refractory gold-bearing pyrite ore from Hualilán (San Juan, Argentina). Pyrite and sphalerite were the main mineral species in the ore with 7% w/w and 8% w/w of iron and zinc and approximately 25 ppm of gold. Leaching experiments (2% w/v ore, 1.8 initial pH, 180 rpm and 30°C) were carried out with the addition of different alternative energy sources (6.67 g/L sulphur powder, 1 g/L ferrous iron, 0.02% w/v yeast extract). Redox potential, pH, ferrous iron concentration and total Fe and Zn were measured regularly. A 100% of iron leaching (after 28 days in the best experimental condition) was observed in some of the cultures. In other systems high zinc release was obtained (100% of dissolution after 28 days in the best experimental condition). Our results strongly suggest that under the correct operating conditions, biooxidation pre-treatment can be used to recover zinc as a subproduct of gold extraction from refractory ore.

Microbial Diversity in a Brazilian Acid Moderate Drainage and Experimental Nickel Bioleaching System

The aim of this work was to determine the microbial diversity of the acid mine drainage (AMD) material collected at an abandoned pyrite mine in Ouro Preto, Brazil. AMD samples were compared to a nickel sulfide column bioleaching pregnant solution which was used as reference. Fluorescent in situ hybridization analyses (FISH) and Denaturing Gradient Gel Electrophoresis (DGGE) were used. FISH analysis was carried out using specific 16S rRNA probes. The extracted DNA was amplified using universal primers for bacterial 16S rRNA genes and analyzed by DGGE. Acidithiobacillus. ferrooxidans was not detected in AMD samples. However, the presence of Acidithiobacillus thiooxidans was confirmed. In other hand, in the bioleaching tanks samples studied, both bacteria species were detected. The non-identified DNA bands were cloned and sequenced for complete characterization.

Assessment of Microbial Patagonian Communities for Using in Heavy Metal Bioremediation

Assessing microbial communities in extreme environments allows the search for novel extremophilic microorganisms that can be of use in the development or improvement of biotechnological processes. Most microbial communities developed in such harsh environments have different heavy metal resistance strategies of importance in some technological applications as biomining but also in the bioremediation of metal-polluted environments. In this chapter we describe the microbial diversity of an acidic, volcanic geothermal environment in Northern Patagonia of Argentina: the Copahue geothermal system, containing different geothermal manifestations with temperatures up to 90 °C and pH values from 2 to 7 under aerobic and anaerobic conditions, provoking an enormous biodiversity. In addition, we report some heavy metal applications of those communities, focusing mainly in the bioprecipitation of heavy metals using sulfate-reducing microorganisms.

FISH Analysis of Bacterial Attachment to Copper Sulfides in Bioleaching Processes

Bioleaching is the biological conversion of an insoluble metal compound into a water soluble form. In this process metal sulfides are oxidized to metal ions and sulfate by acidophilic microorganisms capable of oxidizing Fe2+ and/or sulfur-compounds. The metal solubilization from sulfide minerals is a chemical process which requires Fe3+ reduction. It is an environmentally friendly technique and an economical method for recovering metals that requires low investment and operation costs. In this work we studied the bioleaching of two kinds of acid-soluble copper sulfides, one easily leached by mesophilic bacteria (covellite), and the other one refractory to their activity (chalcopyrite), in acidic media with or without Fe2+ ions. We studied attached and planktonic populations of autotrophic bacteria, such as Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans in pure or mixed cultures. The influence of a heterotrophic microorganism, Acidiphilium cryptum, was also studied. Attachment was evaluated with fluorescence staining and FISH using four specific probes. L. ferrooxidans showed highest initial attachment in all cases. The presence of Ap. cryptum increased the cell attachment compared with the autotrophic pure cultures. It was possible to correlate experimental data with a mechanism of bacterial-metal sulfide oxidation, the polysulfide pathway for acid- soluble metal sulfides.