Iron and magnesium exchange via the low affinity iron transporter in rabbit erythroid cells—exchange rates and the action of valinomycin, diethylstilbestrol and protein kinase inhibitors

Antibiotic resistance genes attenuation in anaerobic microorganisms during iron uptake from zero valent iron: An iron-dependent form of homeostasis and roles as regulators

Zero valent iron (ZVI) has been previously documented to attenuate the propagation of antibiotic resistance genes (ARGs) in microbes, while how ZVI affects the evolution of ARGs remains unclear. Herein, we investigated the influences of ZVI on ARGs dissemination in anaerobic bioreactor treating oxytetracycline (tet) containing wastewater, by deciphering the roles of iron homeostasis and regulatory effects. A net reduction of tet gene targets ranging from 0.75 to 1.88 and 0.67 to 2.08 log unit in intracellular and extracellular DNA was achieved at the optimal dosage of 5 g/L ZVI, whereas 20 g/L ZVI made no effects on ARGs reduction. The reduced ARGs abundance by ZVI was directly related to the inhibited horizontal transfer of ARGs and decreased proliferation of resistant strains (mainly Paludibacter and WCHB1-32). The potential mechanisms included the increased antioxidant capacity, the depressed efflux pump system and the weakened energy driving force by Fur regulon in microbes (especially for Cloacibacterium and Dechloromonas). The negligible influence of 20 g/L ZVI on ARGs reduction was ascribed to the iron-catalyzed oxidative damage and reduced physiological activity. This study firstly illustrated the potential relationships among activation of iron uptake regulator leading to protection against oxidative stress, alternation of physiological metabolisms and reduction of ARGs dissemination. This work extents our understanding about the priority of ZVI in mitigating ARGs proliferation and sheds light on its potential application in wastewater treatment plants.

Low-level free nitrous acid efficiently inhibits the conjugative transfer of antibiotic resistance by altering intracellular ions and disabling transfer apparatus

Recently, the dissemination of antibiotic resistance genes (ARGs) via plasmid-mediated conjugation has been reported to be facilitated by a series of contaminants. This has highlighted potential challenges to the effective control of this principal mode of horizontal transfer. In the present study, we found that low levels (<0.02 mgN/L) of free nitrous acid (FNA) remarkably inhibited (over 90%) the conjugative transfer of plasmid RP4, a model broad-host-range plasmid, between Escherichia coli. The antimicrobial role of FNA at the applied dosages was firstly ruled out, since no dramatic reductions in viabilities of donor or recipient were observed. Instead, FNA appeared to reduce the available intracellular free Mg²⁺, which was confirmed to be triggered by the liberation of intracellular Fe²⁺. These alterations in intracellular Mg²⁺ and Fe²⁺ concentrations were found to significantly limit the available energy for conjugative transfer through suppression of glycolysis by decreasing the activities of glycogen phosphorylase and glyceraldehyde-3-phosphate dehydrogenase and also by diverting the glycolytic flux into the pentose phosphate pathway via activation of glucose-6-phosphate dehydrogenase towards the generation of NADPH rather than ATP. Moreover, RP4-encoding genes responsible for DNA transfer and replication (traI, traJ and trfAp), coupling (traG) and mating pair formation (traF and trbBp) were all significantly down-regulated after FNA treatment, indicating that the transfer apparatus required for plasmid processing and delivery was deactivated. By validating the inhibitory effects of FNA on conjugation in real wastewater, this study highlights a promising method for controlling the dissemination of ARGs in systems such as wastewater treatment plants.

Passive transport pathways for Ca(2+) and Co(2+) in human red blood cells. (57)Co(2+) as a tracer for Ca(2+) influx

The passive transport of calcium and cobalt and their interference were studied in human red cells using (45)Ca and (57)Co as tracers. In ATP-depleted cells, with the ATP concentration reduced to about 1μM, the progress curve for (45)Ca uptake at 1mM rapidly levels off with time, consistent with a residual Ca-pump activity building up at increasing [Ca(T)](c) to reach at [Ca(T)](c) about 5μmol(lcells)(-1) a maximal pump rate that nearly countermands the passive Ca influx, resulting in a linear net uptake at a low level. In ATP-depleted cells treated with vanadate, supposed to cause Ca-pump arrest, a residual pump activity is still present at high [Ca(T)](c). Moreover, vanadate markedly increases the passive Ca(2+) influx. The residual Ca-pump activity in ATP-depleted cells is fuelled by breakdown of the large 2,3-DPG pool, rate-limited by the sustainable ATP-turnover at about 40-50μmol(lcells)(-1)h(-1). The apparent Ca(2+) affinity of the Ca-pump appears to be markedly reduced compared to fed cells. The 2,3-DPG breakdown can be prevented by inhibition of the 2,3-DPG phosphatase by tetrathionate, and under these conditions the (45)Ca uptake is markedly increased and linear with time, with the unidirectional Ca influx at 1mM Ca(2+) estimated at 50-60μmol(lcells)(-1)h(-1). The Ca influx increases with the extracellular Ca(2+) concentration with a saturating component, with K(½(Ca)) about 0.3mM, plus a non-saturating component. From (45)Ca-loaded, ATP-depleted cells the residual Ca-pump can also be detected as a vanadate- and tetrathionate-sensitive efflux. The (45)Ca efflux is markedly accelerated by external Ca(2+), both in control cells and in the presence of vanadate or tetrathionate, suggesting efflux by carrier-mediated Ca/Ca exchange. The (57)Co uptake is similar in fed cells and in ATP-depleted cells (exposed to iodoacetamide), consistent with the notion that Co(2+) is not transported by the Ca-pump. The transporter is thus neither SH-group nor ATP or phosphorylation dependent. The (57)Co uptake shows several similarities with the (45)Ca uptake in ATP-depleted cells supplemented with tetrathionate. The uptake is linear with time, and increases with the cobalt concentration with a saturating component, with J(max) about 16μmol(lcells)(-1)h(-1) and K(½(Co)) about 0.1mM, plus a non-saturating component. The (57)Co and (45)Ca uptake shows mutual inhibition, and at least the stochastic Ca(2+) influx is inhibited by Co(2+). The (57)Co and (45)Ca uptake are both insensitive to the 1,4-dihydropyridine Ca-channel blocker nifedipine, even at 100μM. The (57)Co uptake is increased at high negative membrane potentials, indicating that the uptake is at least partially electrogenic. The (57)Co influx amounts to about half the (45)Ca influx in ATP-depleted cells. It is speculated that the basal Ca(2+) and Co(2+) uptake could be mediated by a common transporter, probably with a channel-like and a carrier-mediated component, and that (57)Co could be useful as a tracer for at least the channel-like Ca(2+) entry pathway in red cells, since it is not itself transported by the Ca-pump and, moreover, is effectively buffered in the cytosol by binding to hemoglobin, without interfering with Ca(2+) buffering. The molecular identity of the putative common transporter(s) remains to be defined.

Cadmium availability to freshwater mussel (Unio tumidus) in the presence of organic matter and UV radiation

The influence of ultraviolet radiation (UV) on cadmium availability to freshwater mussel (Unio tumidus) in the presence of organic matter was investigated. Water solutions containing 1000, 500, and 250 microg x L(-1) of cadmium and 28.8 mg x L(-1) of total organic carbon (TOC) were exposed to ecologically relevant biologically effective UV-A and UV-B irradiances of 1.73 x 10(-6) W x cm(-2) and 1.50 x 10(-5) W x cm(-2) respectively for 12 h. The availability of cadmium was measured directly as Cd concentration in gills, mantle, digestive gland and foot, and indirectly as its impact on the content of essential cations. The concentration of cadmium ions, soluble forms of cadmium, pH and conductivity in UV irradiated solutions were also measured. UV exposures resulted in a decrease of the TOC to 25.9 mg x L(-1), followed by a decrease in the total concentration of Cd soluble forms, increase in the concentration of cadmium bound to particulate matter, and increase in the concentration of free cadmium ions in comparison to non-irradiated mixtures. Mussels from mixtures exposed to UV accumulated more cadmium than specimens from non-irradiated mixtures. This was confirmed by the fluctuations of essential cations, i.e. decreases in the contents of Zn, Ca, Fe and increase of the Cu content. Na/K molar ratios in gills were negatively correlated with cadmium content, while a positive trend occurred in other organs. We suggest that in UV-exposed water more ionic forms of cadmium occur. On the other hand more cadmium is also bound to particulate matter. Our research indicate that the increase of cadmium accumulation in mussels grown in humic acid solutions exposed to UV were most probably related to the increase in the concentration of cadmium bound to particulate matter.

Belgrade rats display liver iron loading

Patients with mutations in divalent metal transporter-1 (DMT1), an intestinal nonheme iron transporter, suffer from microcytic anemia and hepatic iron loading. DMT1 is also mutated in Belgrade rats, an animal model with a thalassemic-like disorder of microcytic anemia with hyperferrinemia. However, aspects of hepatic iron loading in this genetic model are not well characterized. To more fully define the Belgrade rat's iron status, we compared the characteristics of homozygous (b/b) and heterozygous (b/+) rats fed an iron-supplemented diet for 3 wk postweaning. Dietary supplementation with ferrous iron improved the anemia of b/b rats insofar as hematocrits increased from 0.13 (21-d-old) to 0.31 (42-d-old). However, hematocrits remained significantly lower than those of age-matched b/+ rats (0.36 and 0.41 in 21- and 42-d-old heterozygotes, respectively, P < 0.05). Wright's staining of b/b red cells confirmed the hypochromic microcytic nature of Belgrade rats' anemia. The liver iron concentration of 42-d-old b/b rats was greater than in age-matched b/+ rats (5.97 vs. 2.24 mumol/g, P < 0.05). Whereas Perls' Prussian blue iron staining was evident in both periportal and centrilobular regions in 42-d-old b/b liver sections, no staining was observed in age-matched b/+ tissue sections. Quantitative real-time PCR analysis showed that expression of liver hepcidin mRNA in 42-d-old b/b rats was 3-fold greater than age-matched b/+ rats. These results indicate that, similar to human patients with DMT1 mutations, Belgrade rats also display hepatic iron loading. Our data suggest this condition arises from ineffective erythropoiesis.