Influence of the bacterial growth phase on the magnetic properties of magnetosomes synthesized by Magnetospirillum gryphiswaldense.

BACKGROUND: The magnetosome biosynthesis is a genetically controlled process but the physical properties of the magnetosomes can be slightly tuned by modifying the bacterial growth conditions. METHODS: We designed two time-resolved experiments in which iron-starved bacteria at the mid-logarithmic phase are transferred to Fe-supplemented medium to induce the magnetosomes biogenesis along the exponential growth or at the stationary phase. We used flow cytometry to determine the cell concentration, transmission electron microscopy to image the magnetosomes, DC and AC magnetometry methods for the magnetic characterization, and X-ray absorption spectroscopy to analyze the magnetosome structure. RESULTS: When the magnetosomes synthesis occurs during the exponential growth phase, they reach larger sizes and higher monodispersity, displaying a stoichiometric magnetite structure, as fingerprinted by the well defined Verwey temperature. On the contrary, the magnetosomes synthesized at the stationary phase reach smaller sizes and display a smeared Verwey transition, that suggests that these magnetosomes may deviate slightly from the perfect stoichiometry. CONCLUSIONS: Magnetosomes magnetically closer to stoichiometric magnetite are obtained when bacteria start synthesizing them at the exponential growth phase rather than at the stationary phase. GENERAL SIGNIFICANCE: The growth conditions influence the final properties of the biosynthesized magnetosomes. This article is part of a Special Issue entitled "Recent Advances in Bionanomaterials" Guest Editors: Dr. Marie-Louise Saboungi and Dr. Samuel D. Bader.

On the mineral core of ferritin-like proteins: structural and magnetic characterization.

It is generally accepted that the mineral core synthesized by ferritin-like proteins consists of a ferric oxy-hydroxide mineral similar to ferrihydrite in the case of horse spleen ferritin (HoSF) and an oxy-hydroxide-phosphate phase in plant and prokaryotic ferritins. The structure reflects a dynamic process of deposition and dissolution, influenced by different biological, chemical and physical variables. In this work we shed light on this matter by combining a structural (High Resolution Transmission Electron Microscopy (HRTEM) and Fe K-edge X-ray Absorption Spectroscopy (XAS)) and a magnetic study of the mineral core biomineralized by horse spleen ferritin (HoSF) and three prokaryotic ferritin-like proteins: bacterial ferritin (FtnA) and bacterioferritin (Bfr) from Escherichia coli and archaeal ferritin (PfFtn) from Pyrococcus furiosus. The prokaryotic ferritin-like proteins have been studied under native conditions and inside the cells for the sake of preserving their natural attributes. They share with HoSF a nanocrystalline structure rather than an amorphous one as has been frequently reported. However, the presence of phosphorus changes drastically the short-range order and magnetic response of the prokaryotic cores with respect to HoSF. The superparamagnetism observed in HoSF is absent in the prokaryotic proteins, which show a pure atomic-like paramagnetic behaviour attributed to phosphorus breaking the Fe-Fe exchange interaction.

Determination of vanadium accumulation in onion root cells (Allium cepa L) and its correlation with toxicity

The vanadium is a metal that presents great interest from the toxicological point of view, because of the numerous alterations that can take place in different biological systems. This work evaluated the capacity of vanadium accumulation and its correlation with genotoxic effects in root cells of Allium cepa L. The bulbs were cultivated in renovated filtered water each 24 h, at a temperature of 25 +/- 0.5 degrees C, in darkness and constant aeration. Treatments were carried out under the same experimental conditions, using water solutions of vanadium of 25, 50, 75 and 100 microg/g for 0, 12, 24, 48 and 72 h. A control was carried out where metal solution was substituted by distilled water. After the treatment, the meristems were fixed with alcohol--acetic acid (3:1) and stained according to the technique of Feulge n. The capacity of accumulation was determined by GFAAS. The analysis of the results revealed an accumulation of the metal for all times and concentrations. No correlation was presented among vanadium accumulation, growth and mitotic index; however, positive correlation was given with the induction of chromosomic aberrations. In conclusion, vanadium is able to induce cytotoxic effect in the exposed roots, but only genotoxic effect was correlated with metal accumulation.

Determination of vanadium accumulation in onion root cells (Allium cepa L) and its correlation with toxicity

The vanadium is a metal that presents great interest from the toxicological point of view, because of the numerous alterations that can take place in different biological systems. This work evaluated the capacity of vanadium accumulation and its correlation with genotoxic effects in root cells of Allium cepa L. The bulbs were cultivated in renovated filtered water each 24 h, at a temperature of 25 +/- 0.5 degrees C, in darkness and constant aeration. Treatments were carried out under the same experimental conditions, using water solutions of vanadium of 25, 50, 75 and 100 microg/g for 0, 12, 24, 48 and 72 h. A control was carried out where metal solution was substituted by distilled water. After the treatment, the meristems were fixed with alcohol--acetic acid (3:1) and stained according to the technique of Feulge n. The capacity of accumulation was determined by GFAAS. The analysis of the results revealed an accumulation of the metal for all times and concentrations. No correlation was presented among vanadium accumulation, growth and mitotic index; however, positive correlation was given with the induction of chromosomic aberrations. In conclusion, vanadium is able to induce cytotoxic effect in the exposed roots, but only genotoxic effect was correlated with metal accumulation.(AU)

DNA injury induced by 5-aminouracil and caffeine in G2 checkpoints path of higher plant cells.

This work evaluated the qualitative and quantitative cellular changes induced by treatment with 5-aminouracil (5-AU) and a combination of 5-AU and caffeine in plant cells in relation to DNA damage, repaired damage, and residual damage. As biological material, Allium cepa L. root tips were used, grown in filtered water, in darkness, with aeration at constant temperature of 25 degrees C +/- 0.5. Cell populations were synchronized using 5 mM caffeine in order to study the effects of 5-AU and caffeine/5-AU combined treatment on the DNA content and their incidence in the entrance to mitosis. The results showed a delay in the G2 period due to induced DNA damage by the 5-AU and caffeine/5-AU combined treatment, shown by aberrant metaphases, anaphases and telophases. The effect of caffeine in the combined treatment was heightened in spite of lengthening the checkpoints route that retains the cells in G2. The existence of G2 checkpoints was shown in the cell population studied, inducing lesions in the DNA, chromosomic aberrations and cellular instability.

Effect of cadmium on the nucleoli of meristematic cells of onion Allium cepa L: an ultrastructural study.

This study of the effect of cadmium on nucleolar ultrastructure was carried out with meristematic cell populations of Allium cepa L. Meristems, grown at 25 degrees C, were treated with 10 ppm cadmium chloride. Conventional and silver staining techniques were carried out, and the ultrastructure was analyzed using electron microscopy. Observation showed alterations in the nucleoli of the cells that had been treated with cadmium and this effect varied according to the time of exposure to the metal. After 4h of treatment, nucleolar segregation was observed in interphase, probably because of the effect of cadmium on the synthesis of ribosomal RNA precursors. A decrease in the fibrillar to granular component ratio also occurred in the cells exposed to Cd2+ for 8 h. Some changes were observed in the G1 cells; their chromatin still remained very condensed, and prenucleolus bodies remained scattered within the nucleus. At the same time, there was a large amount of interchromatin granules. These changes produced by cadmium resembled those produced during inhibition of RNA synthesis. The fibrillar bodies, another morphologic feature, resulting from a blocked transcription, were also evidenced. All these observations suggest that one of the ways that cadmium exercises its toxicity is by altering the biosynthesis of the preribosomal RNA precursor.