A.R. Lino

Preparation and physicochemical characterization of Ag nanoparticles biosynthesized by Lippia citriodora (Lemon Verbena)

The purpose of this study was to develop a simple biological method for the synthesis of Ag nanoparticles (AgNPs) using Lippia citriodora leaves aqueous extract as reducing agent. Transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDX), X-ray diffraction (XRD), and visible absorption spectroscopy (UV-vis) confirmed the reduction of silver ions to AgNPs. Stable, spherical crystalline AgNPs with well defined dimensions (average size of 15-30 nm) were obtained, on treating aqueous silver nitrate with the plant leaf aqueous extract. The kinetic of particles formation was proportional to the effect of reducing agent concentration and was enhanced by the increase of temperature from 25 degrees C to 95 degrees C. Time, temperature and extract concentration did not influence significantly the shape and size of nanoparticles. In order to identify the compounds responsible for the bioreduction of silver ions and stabilization of the AgNPs formed, we investigated the constituents of L. citriodora aqueous extract by high performance liquid chromatography (HPLC) and mass spectrometry (MS). The main compounds found were verbascoside, isoverbascoside, chrysoeriol-7-O-diglucoronide and luteonin-7-O-diglucoronide. The data obtained suggests that the isoverbascoside compound is responsible for Ag(+) ions reduction and act as capping agents of the nanoparticles afterwards.

Biosynthesis of Crystalline Silver and Gold Nanoparticles by Extremophilic Yeasts

The biosynthesis of Ag and Au nanoparticles (NPs) was investigated using an extremophilic yeast strain isolated from acid mine drainage in Portugal. Three distinct studies were performed, namely, the growth of yeast strain in presence of metal ions, the use of yeast biomass for the metal nanoparticles synthesis, and of the supernatant obtained after 24-hour incubation of yeast biomass in water. The extremophilic strain under study was able to grow up to an Ag ion concentration of 1.5 mM whereas an increase of Au ion concentration over 0.09 mM caused a strong inhibitory effect. A successful route for the metal NPs synthesis was obtained using the yeast biomass. When the washed yeast cells were in contact with Ag or Au solutions, AgNPs smaller than 20 nm were produced, as for the AuNPs diameter ranged from 30 to 100 nm, as determined through transmission electron microscopy and confirmed by energy-dispersive X-ray spectra. The supernatant-based strategy provided evidence that proteins were released to the medium by the yeasts, which could be responsible for the formation and stabilisation of the Ag NPs, although the involvement of the cell wall seems fundamental for AuNPs synthesis.

The influence of the media on the corrosion of mild steel by Desulfovibrio desulfuricans bacteria: an electrochemical study

Abstract Electrochemical studies and weight loss measurements on the biocorrosion of mild steel in the presence and absence of sulphate reducing bacteria (SRB) grown either in lactate/sulphate and or in lactate/nitrate aqueous media, have been performed. Tafel analysis of the quasi-steady state polarisation curves gave the corrosion current densities,jcorr, of 20 and 30 μA cm−2 for mild steel samples in the SRB culture in lactate/sulphate and lactate/nitrate media, respectively. In the absence of SRB the corresponding values of jcorr were 19 and 9 μA cm−2, respectively. Corrosion current densities given by the linear polarisation resistance method were very close to the ones given by Tafel analysis. A comparison of the corrosion rates obtained either from electrochemical or from weight loss data is given for all the media under study. Open circuit potential and redox potentials measured over two days showed great differences for the lactate/sulphate and lactate/nitrate growth media. Scanning electron microscopy (SEM) observations resulted in good correlation with open circuit potential data.

Elemental composition of four farmed fish produced in Portugal

Farmed gilthead sea bream (Sparus aurata), European sea bass (Dicentrarchus labrax), rainbow trout (Oncorhynchus mykiss) and turbot (Psetta maxima) produced in Portugal were analysed in order to characterize their elemental composition. Atomic absorption (flame and cold vapour) and molecular absorption spectrometry techniques were used to determine all the studied elements. Similar patterns of macro, trace and ultra trace elements were observed for all fish species. The main elements were potassium (K), sodium (Na), phosphorus (P), magnesium (Mg) and calcium (Ca), followed by zinc (Zn), iron (Fe), copper (Cu), chromium (Cr), manganese (Mn) and nickel (Ni). Cadmium (Cd), mercury (Hg) and lead (Pb) concentrations, obtained in this study, allow concluding that these species do not present a hazard for human consumption. In addition, they contain almost all essential elements at concentrations sufficient to suit the dietary reference intake. Nevertheless, P. maxima nutritious trace element content is relatively low compared with the other three species.

Anaerobic reduction of a sulfonated azo dye, congo red, by sulfate-reducing bacteria

The capacity for anaerobic decolorization of a sulfonated azo dye, Congo Red, by a strain of a sulfate-reducing bacterium was evaluated. After optimizing the growth rate of the bacteria on a simple carbon source and terminal electron acceptor pair, lactate and sulfate, respectively, the effect of the dye concentration on their growth rate was analyzed. The decolorization rate was affected by the dye concentration in the growth medium. The azo-bond cleavage mechanism of reductive decolorization with the formation of benzidine was consistent with the results, as this metabolite was identified by high-performance liquid chromatography. Several fractions of the culture medium, including lysed cell extracts, were examined for the capacity to reduce the azo dye. This reduction capacity was found in the culture medium in which the cells had previously grown. The results showed that the mechanism of reductive decolorization of this sulfonated azo dye was extracellular and nonenzymatic, consistent with the production of sulfide anion by the microorganisms while growing on lactate and sulfate. The sulfide anions were the cause of the reduction leading to the disappearance of color in the medium. To increase the rate of decolorization, the presence of ferrous ion was also necessary together with the lactate and sulfate substrates.

The influence of the Desulfovibrio desulfuricans 14 ATCC 27774 on the corrosion of mild steel

The involvement of sulphate-reducing bacteria (SRB) in microbially influenced corrosion (MIC) of steel and the serious implications associated with their presence in industrial environments have long been known and extensively described. Desulfovibrio desulfuricans ATCC 27774 is an interesting metabolic case of SRB, as it can use both sulphate and nitrate as respiratory substrates during lactate oxidation. This strain has been extensively studied from both a biochemical and structural point of view but, so far, restricted information is available concerning its role in MIC. This work describes a comparative study of the corrosive aggressivity of ATCC 27774 strain towards mild steel when grown either in lactate/sulphate or lactate/nitrate media. The carbon source and electron acceptors consumption rates were analysed and the metabolic features were correlated with weight loss measurements and SEM observations.

Levels of Toxic Metals in Canned Seafood

ABSTRACT The production of canned fish has decreased in recent years; however, several European countries still consume large amounts of these products. It is well known that such products may contain some toxic metals such as mercury, cadmium and lead. In order to determine the level of these three elements in canned seafood, several products were analyzed (more than 1800 samples). The mean total mercury level was 0.12 ± 0.14 mg/kg wet weight, with the highest content found in canned tuna. However, such values did not exceed the proposed limit for tuna by EU (1.0 mg/kg). All analyzed samples showed lead levels lower than the indicated limits. On the other hand, a few samples (less than 2%) of canned tuna and squid exceeded the limit values proposed for cadmium, 0.1 and 1.0 mg/kg, respectively. Taking into account the way in which these products are consumed, it can be concluded that canned seafood products do not represent a risk in terms of human diet.

Biocorrosion of mild steel by SRB: electrochemical studies

Electrochemical studies of the biocorrosion of mild steel in the presence and absence of sulfate reducing bacteria (SRB) grown in lactate/sulfate and lactate/nitrate aqueous media were performed. Open circuit potential measurements revealed a displacement of the potential in the noble direction in both media. However, regular oscillations in the potential were observed only in the lactate/sulfate medium. SEM micrographs showned pits clearly distributed over the surface of the steel samples exposed to SRB cultures in both media, with small size and more uniform pits in the lactate/sulfate media, in agreement with the open circuit potential data. Cyclic voltammetry clearly shows that the SRBs grown in the lactate/sulfate medium lead to high dissolution rates in the transpassive region with the formation of Fe(III) species.

Characterization of two dissimilatory sulfite reductases from sulfate-reducing bacteria

Mössbauer, EPR, and biochemical techniques were used to characterize two dissimilatory sulfite reductases: desulforubidin fromDesulfovibrio baculatus strain DSM 1743 and desulfoviridin fromDesulfovibrio gigas. For each molecule of desulforubidin, there are two sirohemes and four [4Fe−4S] clusters. The [4Fe−4S] clusters are in the diamagnetic 2+ oxidation state. The sirohemes are high-spin ferric (S=5/2) and each siroheme is exchanged-coupled to a [4Fe−4S]2+ cluster. Such an exchange-coupled siroheme-[4Fe−4S] unit has also been found in the assimilatory sulfite reductase fromEscherichia coli/1/ and in a low-molecular weight sulfite reductase fromDesulfovibrio vulgaris/2/. For each molecule of defulfoviridin, there are two tetrahydroporphyrin groups and four [4Fe−4S]2+ clusters. To our surprise, we discovered that about 80% of the tetrahydroporphyrin groups, however, do not bind iron.