Hexavalent Anions Research Articles

Effect of the Simultaneous Action of Zinc and Chromium on Arthrobacter spp.

Bacteria are regarded as the most effective in the detoxification of heavy metals, being environmental compatible. Metalloresistant bacteria are usually found in nature in highly contaminated environment where they interact with a combination of several toxic metals. For the present research, Arthrobacter oxydans and Arthrobacter globiformis have been isolated from the soil samples of the most polluted regions of Georgia, rich with manganese and iron, and contain co-produced toxic metals such as Cr, V, Zn, Ni, Pb, and Mo. We have studied the effects of the metals with different valence/charge on the metalloresistant Arthrobacter spp., the divalent cation—Zn(II) and the hexavalent anion—Cr(VI). The permanent presence of a nontoxic concentration of zinc alone or zinc together with the subtoxic concentration of chromium at the growth of A. oxydans and A. globiformis as batch culture causes the activation of the zinc primary uptake system transporters from the ZIP family (Zrt1). Chromium does not affect the process. The studied Arthrobacter spp. differ by the character of the activation of the antioxidant defense system. Chromium and zinc concomitant action causes the strongest oxidative stress in the case of A. globiformis that is demonstrated by the increased activity of superoxide dismutase (SOD) and catalase. In the case of A. oxydans, the zinc separate action, and the joint action of zinc and chromium decreases the activity of SOD and catalase. The antioxidant system is active in A. globiformis at the prolonged action of metals (96 h), whereas the cells of A. oxyidans activate the other defense mechanisms to survive.

The adsorption-desorption transition of double-stranded DNA interacting with an oppositely charged dendrimer induced by multivalent anions

The adsorption-desorption transition of DNA in DNA-dendrimer solutions is observed when high-valence anions, such as hexavalent anions, are added to the DNA-dendrimer solutions. In the DNA-dendrimer solutions with low-valence anions, dendrimers bind tightly with the V-shaped double-stranded DNA. When high-valence anions, such as pentavalent or hexavalent anions, are added to the DNA-dendrimer solutions, the double-stranded DNA chains can be stretched straightly and the dendrimers are released from the double-stranded DNA chains. In fact, adding high-valence anions to the solutions can change the charge spatial distribution in the DNA-dendrimer solutions, and weaken the electrostatic interactions between the positively charged dendrimers and the oppositely charged DNA chains. Adsorption-desorption transition of DNA is induced by the overcharging of dendrimers. This investigation is capable of helping us understand how to control effectively the release of DNA in gene/drug delivery because an effective gene delivery for dendrimers includes non-covalent DNA-dendrimer binding and the effective release of DNA in gene therapy.

Biosorption of chromium to fungi

Eighteen fungal strains were isolated from water and soil samples and tested for their ability to enrich chromium. The microorganism with the highest enrichment capacity, a zygomycete (Mucor hiemalis MP/92/3/4), was chosen for detailed investigations. Some basic tests such as the pH-dependence, the kinetics of the enrichment and the metal selectivity were carried out with the two most frequent oxidation states of chromium, the trivalent cation (Cr3+) and the hexavalent anion (CrO42−). With Cr3+ the enrichment showed a saturation kinetic reaching 70% of the maximum capacity after about 30 min, whereas with CrO42− a linear time course with a much lower metal enrichment was observed. The highest level of enrichment for Cr3+ was observed at pH 5.5 (21.4 mg/g dry wt), and for CrO42− at pH 1 (4.3 mg/g dry wt). Investigations concerning the metal enrichment selectivity resulted in the following series of decreasing ion uptake: Cr3+ > Cu2+ > Pb2+ > Ag+ > Al3+ > Co2+ > Zn2+ > Ni2+ > Fe2+ > Mo5+ > Cd2+ > 2− > CrO42− > VO3−, calculated on a molar basis. Trivalent chromium caused a staining of the outer cell wall region in transmission electron microscopy. The localization of chromium in the stained outer layers of the cell wall could be verified by electron energy loss spectroscopy. The enrichment of Cr3+ by M. hiemalis seemed to be mainly a passive biosorption to the cell wall, whereas for the uptake of CrO42− intracellular accumulation as well as biosorption is possible.

Effects of Chromium on Growth and Mineral Nutrition of Soybeans

AbstractChromium additions [0–5 ppm Cr(VI)] to soybeans, Glycine max (L) Merrill, grown in nutrient culture resulted in decreased concentrations and total uptake of Ca, K, P, Fe, and Mn in tops and of K, Mg, P, Fe, and Mn in roots. These effects were often apparent at Cr treatments as low as 0.5 ppm.In soil culture Cr additions [0–60 ppm Cr(VI)] appeared to interfere with the accumulation of Ca, K, Mg, P, B, and Cu by soybean tops, with little or no effect on Fe, Mn, or Zn uptake. These effects were generally first observed at the 5‐ppm Cr treatment.The initial symptoms of Cr toxicity appeared as severe wilting of tops of treated plants.It could not be concluded from the results of these experiments that Cr, as the hexavalent anion, specifically interfered with uptake of Fe or P by plants, as earlier reported.