High Energy Resolution-X-ray Absorption Near Edge Structure Spectroscopy Reveals Zn Ligation in Whole Cell Bacteria

Identifying the zinc (Zn) ligation and coordination environment in complex biological and environmental systems is crucial to understand the role of Zn as a biologically essential but sometimes toxic metal. Most studies on Zn coordination in biological or environmental samples rely on the extended X-ray absorption fine structure (EXAFS) region of a Zn K-edge X-ray absorption spectroscopy (XAS) spectrum. However, EXAFS analysis cannot identify unique nearest neighbors with similar atomic number (i.e., O versus N) and provides little information on Zn ligation. Herein, we demonstrate that high energy resolution-X-ray absorption near edge structure (HR-XANES) spectroscopy enables the direct determination of Zn ligation in whole cell bacteria, providing additional insights lost from EXAFS analysis at a fraction of the scan time and Zn concentration. HR-XANES is a relatively new technique that has improved our understanding of trace metals (e.g., Hg, Cu, and Ce) in dilute systems. This study is the first to show that HR-XANES can unambiguously detect Zn coordination to carboxyl, phosphoryl, imidazole, and/or thiol moieties in model microorganisms.

Physicochemical characterization of ferric pyrophosphate citrate

Iron deficiency is a significant health problem across the world. While many patients benefit from oral iron supplements, some, including those on hemodialysis require intravenous iron therapy to maintain adequate iron levels. Until recently, all iron compounds suitable for parenteral administration were colloidal iron-carbohydrate conjugates that require uptake and processing by macrophages. These compounds are associated with variable risk of anaphylaxis, oxidative stress, and inflammation, depending on their physicochemical characteristics. Ferric pyrophosphate citrate (FPC) is a novel iron compound that was approved for parenteral administration by US Food and Drug Administration in 2015. Here we report the physicochemical characteristics of FPC. FPC is a noncolloidal, highly water soluble, complex iron salt that does not contain a carbohydrate moiety. X-ray absorption spectroscopy data indicate that FPC consists of iron (III) complexed with one pyrophosphate and two citrate molecules in the solid state. This structure is preserved in solution and stable for several months, rendering it suitable for pharmaceutical applications in solid or solution state.

Adsorption of Methylmercury onto Geobacter bemidijensis Bem

The anaerobic bacterium Geobacter bemidijensis Bem has the unique ability to both produce and degrade methylmercury (MeHg). While the adsorption of MeHg onto bacterial surfaces can affect the release of MeHg into aquatic environments as well as the uptake of MeHg for demethylation, the binding of MeHg to the bacterial envelope remains poorly understood. In this study, we quantified the adsorption of MeHg onto G. bemidijensis and applied X-ray absorption spectroscopy (XAS) to elucidate the mechanism of MeHg binding. The results showed MeHg adsorption onto G. bemidijensis cell surfaces was rapid and occurred via complexation to sulfhydryl functional groups. Titration experiments yielded cell surface sulfhydryl concentrations of 3.8 ± 0.2 μmol/g (wet cells). A one-site adsorption model with MeHg binding onto sulfhydryl sites provided excellent fits to adsorption isotherms conducted at different cell densities. The log K binding constant of MeHg onto the sulfhydryl sites was determined to be 10.5 ± 0.4. These findings provide a quantitative framework to describe MeHg binding onto bacterial cell surfaces and elucidate the importance of bacterial cells as possible carriers of adsorbed MeHg in natural aquatic systems.

U(VI) Reduction by Biogenic and Abiotic Hydroxycarbonate Green Rusts: Impacts on U(IV) Speciation and Stability Over Time

Green rusts (GRs) are redox active Fe^II-Fe^III minerals that form in the environment via various biotic and abiotic processes. Although both biogenic (BioGR) and abiotic (ChemGR) GRs have been shown to reduce U^VI, the dynamics of the transformations and the speciation and stability of the resulting U^IV phases are poorly understood. We used carbonate extraction and XAFS spectroscopy to investigate the products of U^VI reduction by BioGR and ChemGR. The results show that both GRs can rapidly remove U^VI from synthetic groundwater via reduction to U^IV. The initial products in the ChemGR system are solids-associated U^IV-carbonate complexes that gradually transform to nanocrystalline uraninite over time, leading to a decrease in the proportion of carbonate-extractable U from ∼95% to ∼10%. In contrast, solid-phase U^IV atoms in the BioGR system remain relatively extractable, nonuraninite U^IV species over the same reaction period. The presence of calcium and carbonate in groundwater significantly increase the extractability of U^IV in the BioGR system. These data provide new insights into the transformations of U under anoxic conditions in groundwater that contains calcium and carbonate, and have major implications for predicting uranium stability within redox dynamic environments and designing approaches for the remediation of uranium-contaminated groundwater.

Association of Vitamin D Levels and type 2 Diabetes Mellitus in Asian Indians is Independent of Obesity

Background A large proportion of subjects with type 2 diabetes mellitus (T2DM) in India are non-obese. Asian-Indian subjects with diabetes have been shown to have low vitamin D levels. Whether low vitamin D levels and T2DM in Asian-Indians is attributable to the associated obesity as in caucasians is unclear. Hence we studied the association of vitamin D levels and T2DM in Asian-Indians with or without obesity.

Methods Total of 213 subjects were recruited in four groups, group 1-Non-obese diabetic, group 2-Non-obese non-diabetic, group 3-Obese diabetic and group 4-Obese non-diabetic. Subjects recruited under various groups were matched for age and sex. Anthropometry, skin-fold thickness, fasting and postprandial plasma glucose, HbA1c, fasting insulin, lipids and vitamin D levels were measured in all study subjects and were compared between the groups.

Results Mean age of study population was 41.23±7.43 years. Mean BMI in groups 1,2,3 and 4 was 21.34±1.41, 20.53±2.27, 27.72±2.94 and 27.62±3.37 kg/m2 respectively. Overall 64.3% study subjects had vitamin D deficiency and 27.7% had insufficient vitamin D levels. Significantly lower vitamin D levels were found in diabetic groups 1 and 3 compared to non-diabetic groups 2 and 4. No significant difference was observed in vitamin D levels between groups 1 and 3. Similarly, no significant difference was observed in vitamin D levels between groups 2 and 4. Vitamin D levels did not show any significant correlation with BMI, waist or body fat.

Conclusion Vitamin D levels do not appear to be related to obesity in diabetic as well non-diabetic Asian-Indian individuals.

X-ray Raman scattering: a new in situ probe of molecular structure during nucleation and crystallization from liquid solutions

X-ray Raman scattering (XRS) has been used for in situ probing of solute molecule speciation in solution during cooling crystallization.

Transformation of zinc-concentrate in surface and subsurface environments: Implications for assessing zinc mobility/toxicity and choosing an optimal remediation strategy

Zinc contamination in near- and sub-surface environments is a serious threat to many ecosystems and to public health. Sufficient understanding of Zn speciation and transport mechanisms is therefore critical to evaluating its risk to the environment and to developing remediation strategies. The geochemical and mineralogical characteristics of contaminated soils in the vicinity of a Zn ore transportation route were thoroughly investigated using a variety of analytical techniques (sequential extraction, XRF, XRD, SEM, and XAFS). Imported Zn-concentrate (ZnS) was deposited in a receiving facility and dispersed over time to the surrounding roadside areas and rice-paddy soils. Subsequent physical and chemical weathering resulted in dispersal into the subsurface. The species identified in the contaminated areas included Zn-sulfide, Zn-carbonate, other O-coordinated Zn-minerals, and Zn species bound to Fe/Mn oxides or clays, as confirmed by XAFS spectroscopy and sequential extraction. The observed transformation from S-coordinated Zn to O-coordinated Zn associated with minerals suggests that this contaminant can change into more soluble and labile forms as a result of weathering. For the purpose of developing a soil washing remediation process, the contaminated samples were extracted with dilute acids. The extraction efficiency increased with the increase of O-coordinated Zn relative to S-coordinated Zn in the sediment. This study demonstrates that improved understanding of Zn speciation in contaminated soils is essential for well-informed decision making regarding metal mobility and toxicity, as well as for choosing an appropriate remediation strategy using soil washing.

Study of microbial growth on silicone tubes after transcanalicular laser-assisted dacryocystorhinostomy and correlation with patency

INTRODUCTION

Intubation in primary transcanalicular laser assisted dacryocystorhinostomy (TCLADCR) is performed to increase the success rates. However, the associated inflammation and infection can have adverse effects.

OBJECTIVE

To study the microbial infection and drug susceptibility of extubated silicone tubes and final anatomical patency in patients undergoing TCLADCR.

MATERIALS AND METHODS

A non-randomised prospective interventional study was conducted in a tertiary care eye centre. The study included twenty consecutive adult patients with primary nasolacrimal duct obstruction. They underwent TCLADCR with bicanalicular silicone intubation. The stents were removed at 2 months and subjected to culture sensitivity, followed by administration of appropriate antimicrobial agents. Main outcome measures studied were the microbial spectrum on the cultured tubes, their sensitivity profile and its correlation with final anatomical patency.

RESULTS

A positive culture was obtained in 100% cases, comprising of normal commensals and pathogenic organisms. Of the total 24 isolates, 16 (66.6%) Gram positive bacteria (75% Staphylococcus aureus) and 8 (33.3%) Gram negative bacteria (commonest E.coli) were found, with 4 tubes having more than one isolate. No fungal growth was seen. Ninety percent success rate was achieved at one year following appropriate antimicrobial therapy except in 2 patients with gram negative isolates who had failed to take the prescribed antibiotics following sensitivity reports. There was no correlation between multiple infections and success rate. However, by using the Fisher exact test, a positive correlation was obtained between appropriate antibiotic treatment and the final anatomical patency (p less than 0.05).

CONCLUSION

Silicone intubation predisposes to microbial growth, which if neglected, can lead to failure of TCLADCR.

Bacteriological profile and their antimicrobial susceptibility pattern in central venous catheter tip culture

Background: Bacterial colonization of central venous catheter (CVC) carries risk of developing catheter-related blood stream infections (CRBSI). The purpose of this study is to find out the frequency of colonization of CVC by different bacterial pathogens and their antibiotic sensitivity pattern.Materials and Methods: A total of 53 CVC tip were received in one-year duration for culture and antibiotic sensitivity pattern. The isolated organisms were identified by standard microbiological procedure and subjected to antimicrobial sensitivity.Results: out of 53 CVC tip sent for culture and sensitivity, 21 (39.6%) showed significant growth. Out of 21 culture positive 52.3% were gram negative bacilli, 33.3% were gram positive cocci, 4.8% were Candida spp. Acenitobacter baumannii and Staphylococcus aureus were frequent pathogens isolated. Gram negative bacteria were less sensitive to antibiotics whereas gram positive bacteria were sensitive to Vancomycin.Conclusion: Though various organisms were isolated as colonizer of CVC, Acenitobacter baumannii is the most common colonizer. Antibiotic resistance has already emerged and represents a major problem.  

Intracellular Hg(0) Oxidation in Desulfovibrio desulfuricans ND132

The disposal of elemental mercury (Hg(0)) wastes in mining and manufacturing areas has caused serious soil and groundwater contamination issues. Under anoxic conditions, certain anaerobic bacteria can oxidize dissolved elemental mercury and convert the oxidized Hg to neurotoxic methylmercury. In this study, we conducted experiments with the Hg-methylating bacterium Desulfovibrio desulfuricans ND132 to elucidate the role of cellular thiols in anaerobic Hg(0) oxidation. The concentrations of cell-surface and intracellular thiols were measured, and specific fractions of D. desulfuricans ND132 were examined for Hg(0) oxidation activity and analyzed with extended X-ray absorption fine structure (EXAFS) spectroscopy. The experimental data indicate that intracellular thiol concentrations are approximately six times higher than those of the cell wall. Cells reacted with a thiol-blocking reagent were severely impaired in Hg(0) oxidation activity. Spheroplasts lacking cell walls rapidly oxidized Hg(0) to Hg(II), while cell wall fragments exhibited low reactivity toward Hg(0). EXAFS analysis of spheroplast samples revealed that multiple different forms of Hg-thiols are produced by the Hg(0) oxidation reaction and that the local coordination environment of the oxidized Hg changes with reaction time. The results of this study indicate that Hg(0) oxidation in D. desulfuricans ND132 is an intracellular process that occurs by reaction with thiol-containing molecules.

The mysterious Zika virus: Adding to the tropical flavivirus mayhem

Until now, known as the demure cousin of dengue virus (DENV) inhabiting Africa, Zika virus (ZIKV) has reinvented itself to cause explosive epidemics captivating the Western hemisphere. The outbreak causing potential for ZIKV was realized when it made its way from Africa to Yap Island Micronesia in 2007, and in French Polynesia in 2013. From there, it moved on to Brazil in 2015. Now ZIKV has infected people in more than 33 countries in Central and South America and the Caribbean. Moreover the epidemiological and subsequent virological association with microcephaly cases in Brazil has prompted the World Health Organization to declare a public health emergency of International Concern. ZIKV shares not only its vector Aedes aegypti with dengue and chikungunya but also the geographic distribution and clinical features, which makes the laboratory confirmation mandatory for definitive diagnosis. The serological cross-reactivity with other Flavivirus, particularly with DENV makes laboratory confirmation challenging and will place additional burden on health systems to establish molecular diagnostic facilities. The evidence of additional nonvector modes of transmission, such as perinatal, sexual as well as transfusion has made preventative strategies more difficult. As ZIKV disease continues to mystify us with several unanswered questions, it calls for coordinated effort of global scientific community to address the ever growing arboviral threat to mankind.

Larger and near-term baby retinopathy: a rare case series

PURPOSE

To report retinopathy in a series of four babies unusually beyond the screening standards reported so far in the literature.

METHODS

During routine screening for retinopathy of prematurity, we detected retinopathy in four babies who were surprisingly bigger and older than the screening standards. The gestational age (GA), birth weight (BW), post menstrual age at first examination and significant perinatal events were noted. The retinopathy details imaged by the RetCam were classified as per ICROP revisited standards.

RESULT

The GA ranged from 36 to 39 weeks and BW from 2.4 to 3.0 kg. Three of them had retinopathy in zone III that regressed spontaneously and one had marked plus with vascular arcades and shunts in zone II that regressed after laser photocoagulation. All of them had fetal distress and multiple systemic comorbidities in the neonatal period.

CONCLUSION

This report makes one aware of the possibility of retinopathy in newborn of older GA and larger BW especially with fetal distress and stormy neonatal course.