A gene of the major facilitator superfamily encodes a transporter for enterobactin (Enb1p) in Saccharomyces cerevisiae

While in fungi iron transport via hydroxamate siderophores has been amply proven, iron transport via enterobactin is largely unknown. Enterobactin is a catecholate-type siderophore produced by several enterobacterial genera grown in severe iron deprivation. By using the KanMX disruption module in vector pUG6 in a fet3 background of Saccharomyces cerevisiae we were able to disrupt the gene YOL158c Sce of the major facilitator super family (MFS) which has been previously described as a gene encoding a membrane transporter of unknown function. Contrary to the parental strain, the disruptant was unable to utilize ferric enterobactin in growth promotion tests and in transport assays using ⁵⁵Fe-enterobactin. All other siderophore transport properties remained unaffected. The results are evidence that in S. cerevisiae the YOL158c Sce gene of the major facilitator super family, now designated ENB1, encodes a transporter protein (Enb1p), which specifically recognizes and transports enterobactin.     

Flux of reduced chemical constituents (Fe2+, Mn2+, NH inf4 sup+ and CH4) and sediment oxygen demand in Lake Erie

Sediment pore water concentrations of Fe²⁺, Mn²⁺, NH _inf4 ^sup+ and CH₄ were analyzed from both diver-collected cores and anin situ equilibration device (peeper) in Lake Erie's central basin. Sediment oxygen demand (SOD) was measured at the same station with a hemispheric chamber (including DO probe and recorder) subtending a known area of sediments. The average SOD was 9.4 mM m⁻² day⁻¹ (0.3 g m⁻² day⁻¹). From pore water gradients within the near-surface zone, the chemical flux across the interface was calculated indirectly using Fick's first law modified for sediments. These calculations, using core and peeper gradients, always showed sediment loss to overlying waters, and variations between the two techniques differed by less than an order of magnitude for Fe²⁺ and CH₄. The transport of these reduced constituents can represent a sizeable oxygen demand, ranging from less than 1% for Fe²⁺ and Mn²⁺ to as high as 26% for NH _inf4 ^sup+ , and 30% for CH₄. The average flux of these constituents could account for about a third of the SOD at the sediment-water interface of this station.     

Production of Ethanol from Maltose by Zymobacter palmae Fermentation

The production of ethanol from maltose by Zymobacter palmae T109 in monoculture fermentations, and in co-culture fermentations together with Zymomonas mobilis B69 was studies. Zymobacter palmae T109, produced 5.5% (w/v) of ethanol when co-cultured with Zymomonas mobilis B69, but Zymobacter palmae T109 produced only 4.9% (w/v) ethanol from 15% (w/v) maltose medium in monoculture fermentation.     

Bacterial iron detoxification at the molecular level

Iron is an essential micronutrient, and, in the case of bacteria, its availability is commonly a growth-limiting factor. However, correct functioning of cells requires that the labile pool of chelatable “free” iron be tightly regulated. Correct metalation of proteins requiring iron as a cofactor demands that such a readily accessible source of iron exist, but overaccumulation results in an oxidative burden that, if unchecked, would lead to cell death. The toxicity of iron stems from its potential to catalyze formation of reactive oxygen species that, in addition to causing damage to biological molecules, can also lead to the formation of reactive nitrogen species. To avoid iron-mediated oxidative stress, bacteria utilize iron-dependent global regulators to sense the iron status of the cell and regulate the expression of proteins involved in the acquisition, storage, and efflux of iron accordingly. Here, we survey the current understanding of the structure and mechanism of the important members of each of these classes of protein. Diversity in the details of iron homeostasis mechanisms reflect the differing nutritional stresses resulting from the wide variety of ecological niches that bacteria inhabit. However, in this review, we seek to highlight the similarities of iron homeostasis between different bacteria, while acknowledging important variations. In this way, we hope to illustrate how bacteria have evolved common approaches to overcome the dual problems of the insolubility and potential toxicity of iron.     

LncRNA MAYA promotes iron overload and hepatocyte senescence through inhibition of YAP in non-alcoholic fatty liver disease

Although recent evidence has shown that hepatocyte senescence plays a crucial role in the pathogenesis and development of non-alcoholic fatty liver disease (NAFLD), the mechanism is still not clear. The purpose of this study was to investigate the signal transduction pathways involved in the senescence of hepatocyte, in order to provide a potential strategy for blocking the process of NAFLD. The results confirmed that hepatocyte senescence occurred in HFD-fed Golden hamsters and PA-treated LO2 cells as manifested by increased levels of senescence marker SA-β-gal, p16 and p21, heterochromatin marker H3K9me3, DNA damage marker γ-H2AX and decreased activity of telomerase. Further studies demonstrated that iron overload could promote the senescence of hepatocyte, whereas the overexpression of Yes-associated protein (YAP) could blunt iron overload and alleviate the senescence of hepatocyte. Of importance, depression of lncRNA MAYA (MAYA) reduced iron overload and cellular senescence via promotion of YAP in PA-treated hepatocytes. These effects were further supported by in vivo experiments. In conclusion, these data suggested that inhibition of MAYA could up-regulate YAP, which might repress hepatocyte senescence through modulating iron overload. In addition, these findings provided a promising option for heading off the development of NAFLD by abrogating hepatocyte senescence.     

Chelated iron sources are inhibitors of Pseudomonas aeruginosa biofilms and distribute efficiently in an in vitro model of drug delivery to the human lung

Aims:  To determine whether chelated sources of ferric iron were efficient inhibitors of biofilm formation in Pseudomonas aeruginosa and might be suitable for drug delivery to the lungs of cystic fibrosis (CF) patients via nebulization.
Methods and Results:  The response of P. aeruginosa biofilms to elevated iron concentrations in the form of eight structurally varied iron chelators in a microtitre plate assay for biofilm production was examined in the lab. Among these iron chelates, picolinic acid and acetohydroxamic acid-chelated iron were able to effectively thwart biofilm production in P. aeruginosa PA14 and in 20 clinical isolates of P. aeruginosa from a local hospital. The chelated iron sources showed excellent distribution in an Anderson cascade impactor model of particle size distribution in the human lung.
Conclusions:  Ferric picolinate and ferric acetohydroxamate are effective anti-biofilm compounds against both lab and clinical strains of P. aeruginosa and are readily nebulized into particles of suitable size for lung delivery.
Significance and Impact of the Study:  The data herein serve both to solidify the growing base of literature correlating high iron levels with biofilm inhibition in P. aeruginosa and to highlight the potential of these chelators as nebulized agents to combat biofilms of P. aeruginosa in CF patients.     

SCREENING OF IRON- AND ZINC-ENRICHED YEAST STRAIN AND OPTIMIZATION OF CULTIVATION CONDITIONS

Saccharomyces cerevisiae LN-17 was selected from 26 kinds of primary yeast strains that belong to different genera and species. The iron- and zinc-enriched capability of strain LN-17 was higher than the others. The highest iron and zinc contents of the strain were obtained when the strain grew up under the following conditions: The strain was incubated (5%, v/v) in 50 mL wort medium (pH 6.0) with 100 mg/L Fe ion and 120 mg/L Zn ion. The medium was loaded into a 250-mL Erlenmeyer flask and shaken in a rotary shaker (200 rpm) at 30°C for 60 h. Ferrous sulfate and zinc sulfate were chosen as the source of Fe and Zn. The Fe and Zn contents of the dry cells were determined by atomic absorption spectrum analysis. Under the optimized cultivation conditions, the Fe and Zn contents reached 7.854 mg/g dry cells and 4.976 mg/g dry cells.     

Soybean ferritin: isolation, characterization, and free radical generation

The main aim of this work was to assess the multi-task role of ferritin(Ft)in the oxidative metabolism of soybean(Glycine max).Soybean seeds incubated for 24 h yielded 41 ± 5 μg Ft/g fresh weight.The rate of in vitro incorporation of iron(Fe)into Ft was tested by supplementing the reaction medium with physiological Fe chelators.The control rate,observed in the presence of 100 μM Fe,was not significantly different from the values observed in the presence of 100 μM Fe-his.However,it was significantly higher in the presence of 100 μM Fe-citrate(approximately 4.5-fold)or of 100 μM Fe-ATP(approximately 14-fold).Moreover,a substantial decrease in the Trp-dependent fluorescence of the Ft protein was determined during Fe uptake from Fe-citrate,as compared with the control.On the other hand,Ft addition to homogenates from soybean embryonic axes reduced endogenously generated ascorbyl radical,according to its capacity for Fe uptake.The data presented here suggest that Ft could be involved in the generation of free radicals,such as hydroxyl radical,by Fe-catalyzed reactions.Moreover,the scavenging of these radicals by Ft itself could then lead to protein damage.However,Ft could also prevent cellular damage by the uptake of catalytically active Fe.     

Characterizing and modeling hydrogen sulfide production in anaerobic digestion of livestock manure,agro-industrial wastes,and wastewater sludge

Hydrogen sulfide (H₂S) is the most undesirable inorganic gas in biogas from anaerobic digestion (AD). However, H₂S production in AD is complex and understanding of its processes is still limited. This study performed six controlled batch anaerobic co-digestion experiments to investigate H₂S production. Materials were obtained from four field anaerobic digester systems and co-digestion feedstocks from agroindustry. An additional precipitation experiment was conducted to further examine H₂S production dynamics. Digesters containing highly soluble, carbohydrate-based wastes had a high H₂S final specific production (FSP) value. Additionally, the FSP values were negatively correlated with the initial Fe(II):S ratios in the digester liquid of the batch tests. The precipitation experiment indicated that iron sulfide precipitation was preferred in the presence of an anaerobic community. The H₂S production as a time series was successfully modeled using a generalized additive model (R² > 0.82). This study revealed that sulfate, phosphorus, and iron concentrations are important predictors and potential inhibitors of H₂S production in AD. Further examination of real-time H₂S modeling in AD is warranted.     

Root iron plaque formation and characteristics under N2 flushing and its effects on translocation of Zn and Cd in paddy rice seedlings (Oryza sativa)

Background and Aims

Anoxic conditions are seldom considered in root iron plaque induction of wetland plants in hydroponic experiments, but such conditions are essential for root iron plaque formation in the field. Although ferrous ion availability and root radial oxygen loss capacity are generally taken into account, neglect of anoxic conditions in root iron plaque formation might lead to an under- or over-estimate of their functional effects, such as blocking toxic metal uptake. This study hypothesized that anoxic conditions would influence root iron plaque formation characteristics and translocation of Zn and Cd by rice seedlings.

Methods

A hydroponic culture was used to grow rice seedlings and a non-disruptive approach for blocking air exchange between the atmosphere and the induction solution matrix was applied for root iron plaque formation, namely flushing the headspace of the induction solution with N₂ during root iron plaque induction. Zn and Cd were spiked into the solution after root iron plaque formation, and translocation of both metals was determined.

Key Results

Blocking air exchange between the atmosphere and the nutrient solution by N₂ flushing increased root plaque Fe content by between 11 and 77 % (average 31 %). The N₂ flushing treatment generated root iron plaques with a smoother surface than the non-N₂ flushing treatment, as observed by scanning electron microscopy, but Fe oxyhydroxides coating the rice seedling roots were amorphous. The root iron plaques sequestrated Zn and Cd and the N₂ flushing enhanced this effect by approx. 17 % for Zn and 71 % for Cd, calculated by both single and combined additions of Zn and Cd.

Conclusions

Blocking of oxygen intrusion into the nutrient solution via N₂ flushing enhanced root iron plaque formation and increased Cd and Zn sequestration in the iron plaques of rice seedlings. This study suggests that hydroponic studies that do not consider redox potential in the induction matrices might lead to an under-estimate of metal sequestration by root iron plaques of wetland plants.