Unravelling Metal Speciation in the Microenvironment Surrounding Phytoplankton Cells to Improve Predictions of Metal Bioavailability.

A lack of knowledge on metal speciation in the microenvironment surrounding phytoplankton cells (i.e., the phycosphere) represents an impediment to accurately predicting metal bioavailability. Phycosphere pH and O2 concentrations from a diversity of algae species were compiled. For marine algae in the light, the average increases were 0.32 pH units and 0.17 mM O2 in the phycosphere, whereas in the dark the average decreases were 0.10 pH units and 0.03 mM O2, in comparison to bulk seawater. In freshwater algae, the phycosphere pH increased by 1.28 units, whereas O2 increased by 0.38 mM in the light. Equilibrium modeling showed that the pH alteration influenced the chemical species distribution (i.e., free ion, inorganic complexes, and organic complexes) of Al, Cd, Co, Cu, Fe, Hg, Mn, Ni, Pb, Sc, Sm, and Zn in the phycosphere, and the O2 fluctuation increased oxidation rates of Cu(I), Fe(II) and Mn(II) from 2 to 938-fold. The pH/O2-induced changes in phycosphere metal chemistry were larger for freshwater algae than for marine species. Reanalyses of algal metal uptake data in the literature showed that uptake of the trivalent metals (Sc, Sm and Fe), in addition to divalent metals, can be better predicted after considering the phycosphere chemistry.

PEEK versus titanium cages in lateral lumbar interbody fusion: a comparative analysis of subsidence.

OBJECTIVE: The authors have provided a review of radiographic subsidence after lateral lumbar interbody fusion (LLIF) as a comparative analysis between titanium and polyetheretherketone (PEEK) cages. Many authors describe a reluctance to use titanium cages in spinal fusion secondary to subsidence concerns due to the increased modulus of elasticity of metal cages. The authors intend for this report to provide observational data regarding the juxtaposition of these two materials in the LLIF domain. METHODS: A retrospective review of a prospectively maintained database identified 113 consecutive patients undergoing lateral fusion for degenerative indications from January to December 2017. The surgeons performing the cage implantations were two orthopedic spine surgeons and two neurosurgeons. Plain standing radiographs were obtained at 1-2 weeks, 8-12 weeks, and 12 months postoperatively. Using a validated grading system, interbody subsidence into the endplates was graded at these time points on a scale of 0 to III. The primary outcome measure was subsidence between the two groups. Secondary outcomes were analyzed as well. RESULTS: Of the 113 patients in the sample, groups receiving PEEK and titanium implants were closely matched at 57 and 56 patients, respectively. Cumulatively, 156 cages were inserted and recombinant human bone morphogenetic protein-2 (rhBMP-2) was used in 38.1%. The average patient age was 60.4 years and average follow-up was 75.1 weeks. Subsidence in the titanium group in this study was less common than in the PEEK cage group. At early follow-up, groups had similar subsidence outcomes. Statistical significance was reached at the 8- to 12-week and 52-week follow-ups, demonstrating more subsidence in the PEEK cage group than the titanium cage group. rhBMP-2 usage was also highly correlated with higher subsidence rates at all 3 follow-up time points. Age was correlated with higher subsidence rates in univariate and multivariate analysis. CONCLUSIONS: Titanium cages were associated with lower subsidence rates than PEEK cages in this investigation. Usage of rhBMP-2 was also robustly associated with higher endplate subsidence. Each additional year of age correlated with an increased subsidence risk. Subsidence in LLIF is likely a response to a myriad of factors that include but are certainly not limited to cage material. Hence, the avoidance of titanium interbody implants secondary solely to concerns over a modulus of elasticity likely overlooks other variables of equal or greater importance.

Why Does Cysteine Enhance Metal Uptake by Phytoplankton in Seawater but Not in Freshwater?

Low-molecular-weight weak ligands such as cysteine have been shown to enhance metal uptake by marine phytoplankton in the presence of strong ligands, but the effect is not observed in freshwater. We hypothesized that these contrasting results might be caused by local cysteine degradation and a Ca effect on metal-ligand exchange kinetics in the boundary layer surrounding the algal cells; newly liberated free metal ions cannot be immediately complexed in seawater by Ca-bound strong ligands but can be rapidly complexed by free ligands at low-Ca levels. The present results consistently support this hypothesis. At constant bulk Cd2+ concentrations, buffered by strong ligands: (1) at 50 mM Ca, cysteine addition significantly enhanced Cd uptake in high-Ca preacclimated euryhaline Chlamydomonas reinhardtii (cultured with cysteine as a nitrogen source to enhance local Cd2+ liberation via cysteine degradation); (2) at 0.07 mM Ca, this enhancement was not observed in the algae; (3) at 50 mM Ca, the enhancement disappeared when C. reinhardtii were cultured with ammonium (to inhibit cysteine degradation and local Cd2+ liberation); (4) cysteine addition did not enhance Cd uptake by cysteine-cultured marine Thalassiosira weissflogii when the concentration of immediately reacting strong ligands was sufficient to complex local Cd2+ liberation.

Uptake and subcellular distribution of aluminum in a marine diatom.

Aluminum (Al) is widespread in the environment including the ocean. The effects of Al on marine organisms have attracted more and more attention in recent years. However, the mechanisms of uptake of Al by marine organisms and the subcellular distribution of Al once assimilated are unknown. Here we report the uptake and subcellular distribution of Al in a marine diatom Thalassiosira weissflogii. Short-term (< 120 min) uptake experiments showed that the Al uptake rate by the diatom was 0.033 ±â€¯0.013 fmol-1 cell-1 min-1 (internalization flux normalized to the exposure Al concentration of 2 µM = 0.034 ±â€¯0.013 nmol m-2 min-1 nM-1). Subcellular fractionation experiments showed that the internalized Al was partitioned to subcellular components in the following order: granules (69 ±â€¯5%) > debris (17 ±â€¯4%) > organelles (12 ±â€¯2%) > heat-stable peptides (HSP) (~2%) > heat-denaturable proteins (HDP) (< 1%), indicating that the majority of intracellular Al was detoxified and stored in inorganic forms. The subcellular distribution of Al in the diatom is different from that of Al in freshwater green algae, in which most of the internalized Al is partitioned to organelles. We also evaluated an artificial seawater-based EDTA rinse solution to remove Al adsorbed on the diatom cell surface. Overall, our study provides new information to understand the mechanisms of uptake of Al by marine diatoms, and the mechanisms responsible for the biological effects (both toxic and beneficial) of Al on the growth of marine phytoplankton, especially diatoms.

Chemical Conditions in the Boundary Layer Surrounding Phytoplankton Cells Modify Cadmium Bioavailability.

In this study we tested the hypothesis that metal uptake by unicellular algae may be affected by changes in metal speciation in the boundary layer surrounding the algal cells. The freshwater alga Chlamydomonas reinhardtii was preacclimated to different N nutrition regimes; changes in N nutrition are known to change the nature of extracellular metabolites (e.g., reactive oxygen species "ROS", and OH-) and thus boundary layer chemical conditions. Specifically, at a constant bulk free Cd2+ concentration, Cd uptake by N-starved algae in cysteine-buffered solution was significantly higher than that in NTA-buffered solution. This enhancement was likely due to an increase of the free Cd2+ concentration in the boundary layer, resulting from localized cysteine oxidation by ROS released from these algae. On the other hand, Cd uptake was markedly lower when the free Cd2+ concentration near cell surface decreased as a result of an increase in the boundary layer pH of nitrate-acclimated algae or enhanced localized metal complexation. The results imply that redox, acid-base and metal complexation processes in the boundary layer differ from those in bulk water, even under chemically stable bulk conditions, and the boundary layer effect may well be of significance to phytoplankton acquisition of other trace metals.

Short-term outcomes of lateral lumbar interbody fusion without decompression for the treatment of symptomatic degenerative spondylolisthesis at L4-5.

OBJECTIVE Recently, authors have called into question the utility and complication index of the lateral lumbar interbody fusion procedure at the L4-5 level. Furthermore, the need for direct decompression has also been debated. Here, the authors report the clinical and radiographic outcomes of transpsoas lumbar interbody fusion, relying only on indirect decompression to treat patients with neurogenic claudication secondary to Grade 1 and 2 spondylolisthesis at the L4-5 level. METHODS The authors conducted a retrospective evaluation of 18 consecutive patients with Grade 1 or 2 spondylolisthesis from a prospectively maintained database. All patients underwent a transpsoas approach, followed by posterior percutaneous instrumentation without decompression. The Oswestry Disability Index (ODI) and SF-12 were administered during the clinical evaluations. Radiographic evaluation was also performed. The mean follow-up was 6.2 months. RESULTS Fifteen patients with Grade 1 and 3 patients with Grade 2 spondylolisthesis were identified and underwent fusion at a total of 20 levels. The mean operative time was 165 minutes for the combined anterior and posterior phases of the operation. The estimated blood loss was 113 ml. The most common cage width in the anteroposterior dimension was 22 mm (78%). Anterior thigh dysesthesia was identified on detailed sensory evaluation in 6 of 18 patients (33%); all patients experienced resolution within 6 months postoperatively. No patient had lasting sensory loss or motor deficit. The average ODI score improved 26 points by the 6-month follow-up. At the 6-month follow-up, the SF-12 mean Physical and Mental Component Summary scores improved by 11.9% and 9.6%, respectively. No patient required additional decompression postoperatively. CONCLUSIONS This study offers clinical results to establish lateral lumbar interbody fusion as an effective technique for the treatment of Grade 1 or 2 degenerative spondylolisthesis at L4-5. The use of this surgical approach provides a minimally invasive solution that offers excellent arthrodesis rates as well as favorable clinical and radiological outcomes, with low rates of postoperative complications. However, adhering to the techniques of transpsoas lateral surgery, such as minimal table break, an initial look-and-see approach to the psoas, clear identification of the plexus, minimal cranial caudal expansion of the retractor, mobilization of any traversing sensory nerves, and total psoas dilation times less than 20 minutes, ensures the lowest possible complication profile for both visceral and neural injuries even in the narrow safe zones when accessing the L4-5 disc space in patients with degenerative spondylolisthesis.

Interactions Between Silver Nanoparticles/Silver Ions and Liposomes: Evaluation of the Potential Passive Diffusion of Silver and Effects of Speciation.

Silver nanoparticles, used mainly for their antibacterial properties, are among the most common manufactured nanomaterials. How they interact with aquatic organisms, especially how they cross biological membranes, remains uncertain. Free Ag+ ions, released from these nanoparticles, are known to play an important role in their overall bioavailability. In this project, we have studied the uptake of dissolved and nanoparticulate silver by liposomes. These unilamellar vesicles, composed of phospholipids, have long been used as models for natural biological membranes, notably to study the potential uptake of solutes by passive diffusion through the phospholipid bilayer. The liposomes were synthesized using extrusion techniques and were exposed over time to dissolved silver under different conditions where Ag+, AgS2O3-, or AgCl0 were the dominant species. Similar experiments were conducted with the complexes HgCl 2 0 and Cd(DDC) 2 0 , both of which are hydrophobic and known to diffuse passively through biological membranes. The uptake kinetics of Ag+, HgCl 2 0 , and Cd(DDC) 2 0 show no increase in internalized concentrations over time, unlike AgS2O3- and AgCl0, which appear to pass through the phospholipid bilayer. These results are in contradiction with our initial hypothesis that lipophilic Hg and Cd complexes would be able to cross the membrane, whereas silver would not. Encapsulated tritiated water inside the liposomes was shown to rapidly diffuse through the lipid bilayer, suggesting a high permeability. We hypothesize that monovalent anions or complexes as well as small neutral complexes with a strong dipole can diffuse through our model membrane. Finally, liposomes were exposed to 5-nm polyvinylpyrrolidone-coated silver nanoparticles over time. No significant uptake of nanoparticulate silver was observed. Neither disruption of the membrane nor invagination of nanoparticles into the liposomes was observed. This suggests that the main risk caused by AgNPs for nonendocytotic biological cells would be the elevation of the free silver concentration near the membrane surface due to adsorption of AgNPs and subsequent oxidation/dissolution.

Metal (Ag, Cd, Cu, Ni, Tl, and Zn) Binding to Cytosolic Biomolecules in Field-Collected Larvae of the Insect Chaoborus.

We characterized the biomolecules involved in handling cytosolic metals in larvae of the phantom midge (Chaoborus) collected from five mining-impacted lakes by determining the distribution of Ag, Cd, Cu, Ni, Tl, and Zn among pools of various molecular weights (HMW: high molecular weight, >670-40 kDa; MMW: medium molecular weight, 40-<1.3 kDa; LMW: low molecular weight, <1.3 kDa). Appreciable concentrations of nonessential metals were found in the potentially metal-sensitive HMW (Ag and Ni) and LMW (Tl) pools, whereas the MMW pool, which includes metallothioneins (MTs) and metallothionein-like proteins and peptides (MTLPs), appears to be involved in Ag and Cd detoxification. Higher-resolution fractionation of the heat-stable protein (HSP) fraction revealed further differences in the partitioning of nonessential metals (i.e., Ag = Cd ≠ Ni ≠ Tl). These results provide unprecedented details about the metal-handling strategies employed by a metal-tolerant, freshwater animal in a field situation.

International classification of disease clinical modification 9 modeling of a patient comorbidity score predicts incidence of perioperative complications in a nationwide inpatient sample assessment of complications in spine surgery.

OF BACKGROUND DATA: A patient comorbidity score (RCS) was developed from a prospective study of complications occurring in spine surgery patients. OBJECTIVE: To validate the RCS, we present an International Classification of Disease Clinical Modification (ICD-CM)-9 model of the score and correlate the score with complication incidence in a group of patients from the Nationwide Inpatient Sample database. We compare the predictive value of the score with the Charlson index. STUDY DESIGN: We conducted a retrospective assessment of Nationwide Inpatient Sample patients undergoing cervical or thoracolumbar spine surgery for degenerative pathology from 2002 to 2009. METHODS: We generated an ICD-9-CM coding-based model of our prospectively derived RCS, categorizing diagnostic codes to represent relevant comorbidities. Multivariate models were constructed to eliminate the least significant variables. ICD-9-CM coding was also used to calculate a Charlson comorbidity score for each patient. The accuracy of the RCS was compared with the Charlson index through the use of a receiver-operating curve. RESULTS: A total of 352,535 patients undergoing 369,454 spine procedures for degenerative disease were gathered. Hypertension and hyperlipidemia were the most common comorbidities. Cervical procedures resulted in 8286 complications (4.50%), whereas thoracolumbar procedures produced 25,118 complications (13.55%). Increasing RCS correlated linearly with increasing complication incidence (odds ratio [OR] 1.11; 95% confidence interval [CI], 1.10-1.13; P<0.0001). Logistic regression revealed that neurological deficit, cardiac conditions, and drug or alcohol use had greatest association with complication occurrence. The Charlson index also correlated with complication occurrence in both cervical (OR 1.25; 95% CI, 1.23-1.27) and thoracolumbar (OR 1.11; 95% CI, 1.10-1.12) patient groups. Receiver-operating curve analysis allowed a comparison of accuracy of the indices by comparing predictive values. The RCS performed as well as the Charlson index in predicting complication occurrence in both cervical and thoracic spine patients. CONCLUSIONS: ICD-9-based modeling validated that RCS correlates with complication occurrence. The RCS performed as well as the Charlson index in predicting risk of complication in spine patients.

In the presence of fluoride, free Sc³âº is not a good predictor of Sc bioaccumulation by two unicellular algae: possible role of fluoro-complexes.

We investigated the effect of fluoride complexation on scandium accumulation by two unicellular algae, Chlamydomonas reinhardtii and Pseudokirchneriella subcapitata. This trivalent metal was selected for its chemical similarities with aluminum and for its convenient radioisotope (Sc-46), which can be used as a tracer in short-term bioaccumulation studies. Scandium surface-bound concentrations (Sc(ads)) and uptake fluxes (J(int)) were estimated in the two algae over short-term (<1 h) exposures at pH 5 and in the presence of 0 to 40 µM F(-). Although the computed proportion of dissolved Sc(3+) dropped from 20% to 0.01% over this [F(-)] range, Sc(ads) and J(int) values for both algae decreased only slightly, suggesting a participation of Sc fluoro-complexes in both processes. Surface adsorption and uptake of fluoride complexes with aluminum have been reported in the literature. These observations are not taken into account by current models for trace metal bioaccumulation (e.g., the biotic ligand model). Results from a previous study, where the effects of pH on Sc uptake were investigated, suggested that Sc hydroxo-complexes were internalized by C. reinhardtii. There is thus growing evidence that the free ion concentration may not be adequate to predict the accumulation of Sc (and potentially of other trivalent metals) in aquatic organisms.

Predicting cadmium accumulation and toxicity in a green alga in the presence of varying essential element concentrations using a biotic ligand model.

This study refines the Biotic Ligand Model (BLM) approach by integrating the modulating effects of various essential elements on cadmium (Cd) uptake kinetics in the freshwater alga Chlamydomonas reinhardtii. The algae were first acclimated to a low (LM) or high trace metal (HM) medium as well as to low or high free Cd(2+) and Co(2+) concentrations. The short-term Cd transport capacity and affinity were then quantified in exposure media in which essential trace metals and calcium concentrations were manipulated. The results show that after acclimation to the LM medium, exposure to high free Ca(2+) decreases the capacity of the Cd transport system. Also, acclimation to high (10(-9) M free Co(2+)) or low (10(-11) M free Co(2+)) did not significantly affect Cd uptake rates. When all essential trace metals were simultaneously increased in the acclimation (and exposure) medium, the capacity of the transport system decreased by ∼ 60%, a decrease close to that due to high [Zn(2+)] alone, suggesting that Zn is the main trace metal modulator of the Cd transporter capacity. Changes in Cd toxicity (growth inhibition) in the presence of different essential trace metal concentrations were strongly related to the steady-state concentration of intracellular cadmium, regardless of the cell's nutritional state. Our BLM incorporating the physiological effects of Ca(2+) and other trace metals predicts steady-state Cd accumulation in the presence of varying concentrations of essential elements at 7 nM free Cd(2+), but predictions over a wide range of free [Cd(2+)] proved to be more difficult.

Uptake and subcellular distributions of cadmium and selenium in transplanted aquatic insect larvae.

We transplanted larvae of the phantom midge Chaoborus punctipennis from a lake having lower concentrations of Cd and Se (Lake Dasserat) to a more contaminated lake (Lake Dufault) located near a metal smelter in Rouyn-Noranda, Quebec. Transplanted individuals were held in mesh mesocosms for up to 16 days where they were fed with indigenous contaminated zooplankton. Larval Cd and Se burdens increased over time, and came to equal those measured in indigenous C. punctipennis from contaminated Lake Dufault. Larval Se burdens increased steadily, whereas those of Cd showed an initial lag phase that we explain by a change in the efficiency with which this insect assimilated Cd from its prey. We measured Cd and Se in subcellular fractions and found that larvae sequestered the majority (60%) of the incoming Cd in a detoxified fraction containing metal-binding proteins, whereas a minority of this nonessential metal was in sensitive fractions (20%). In contrast, a much higher proportion of the essential element Se (40%) was apportioned to metabolically active sensitive fractions. Larvae took up equimolar quantities of these elements over the course of the experiment. Likewise, Cd and Se concentrations in wild larvae were equimolar, which suggests that they are exposed to equimolar bioavailable concentrations of these elements in our study lakes.

Lead (Pb) and copper (Cu) share a common uptake transporter in the unicellular alga Chlamydomonas reinhardtii.

The unicellular alga Chlamydomonas reinhardtii has a very high rate of lead (Pb) internalization and is known to be highly sensitive to dissolved Pb. However, the transport pathway that this metal uses to cross cellular membranes in microalgae is still unknown. To identify the Pb(2+) transport pathway in C. reinhartdii, we performed several competition experiments with environmentally relevant concentrations of Pb(2+) (~10 nM) and a variety of divalent cations. Among the essential trace metals tested, cobalt, manganese, nickel and zinc had no effect on Pb internalization. A greater than tenfold increase in the concentrations of the major ions calcium and magnesium led to a slight decrease (~34 %) in short-term Pb internalization by the algae. Copper (Cu) was even more effective: at a Cu concentration 50 times higher than that of Pb, Pb internalization by the algae decreased by 87 %. Pre-exposure of the algae to Cu showed that the effect was not due to a physiological effect of Cu on the algae, but rather to competition for the same transporter. A reciprocal effect of Pb on Cu internalization was also observed. These results suggest that Cu and Pb share a common transport pathway in C. reinhardtii at environmentally relevant metal concentrations.

Adjunctive Use of Bone Growth Stimulation Increases Cervical Spine Fusion Rates in Patients at Risk for Pseudarthrosis.

STUDY DESIGN: A prospective multicenter clinical trial (NCT03177473) was conducted with a retrospective cohort used as a control arm. OBJECTIVE: The purpose of this study was to evaluate cervical spine fusion rates in subjects with risk factors for pseudarthrosis who received pulsed electromagnetic field (PEMF) treatment. SUMMARY OF BACKGROUND DATA: Certain risk factors predispose patients to pseudarthrosis, which is associated with prolonged pain, reduced function, and decreased quality of life. METHODS: Subjects in the PEMF group were treated with PEMF for 6 months postoperatively. The primary outcome measure was fusion status at the 12-month follow-up period. Fusion status was determined using anterior/posterior, lateral, and flexion/extension radiographs and computed tomography (without contrast). RESULTS: A total of 213 patients were evaluated (PEMF, n=160; Control, n=53). At baseline, the PEMF group had a higher percentage of subjects who used nicotine ( P =0.01), had osteoporosis ( P <0.05), multi-level disease ( P <0.0001), and were >65 years of age ( P =0.01). The PEMF group showed over two-fold higher percentage of subjects that had ≥3 risk factors (n=92/160, 57.5%) compared with the control group (n=14/53, 26.4%). At the 12-month follow-up, the PEMF group demonstrated significantly higher fusion rates compared with the control (90.0% vs. 60.4%, P <0.05). A statistically significant improvement in fusion rate was observed in PEMF subjects with multi-level surgery ( P <0.0001) and high BMI (>30 kg/m 2 ; P =0.0021) when compared with the control group. No significant safety concerns were observed. CONCLUSIONS: Adjunctive use of PEMF stimulation provides significant improvements in cervical spine fusion rates in subjects having risk factors for pseudarthrosis. When compared with control subjects that did not use PEMF stimulation, treated subjects showed improved fusion outcomes despite being older, having more risk factors for pseudarthrosis, and undergoing more complex surgeries.

The biotic ligand model can successfully predict the uptake of a trivalent ion by a unicellular alga below pH 6.50 but not above: possible role of hydroxo-species.

In many reported cases, the biotic ligand model (BLM) has been shown to predict the bioavailability of divalent metals toward aquatic biota successfully. However, studies on the bioavailability of nonessential trivalent metals, including aluminum (Al), are relatively scarce. In the present study, short-term scandium (Sc) internalization fluxes (Jint) were measured in Chlamydomonas reinhardtii in order to explore the applicability of the BLM to trivalent metals. Scandium was selected for its chemical similarities with Al and for its convenient radio-isotope (Sc-46). Apparent affinity constants of Sc(3+) with membrane transport sites (KSc-Rcell app) were surprisingly high, ranging from 10(8.08) M(-1) to 10(13.95) M(-1) over the pH range from 4.50 to 7.90. The competition of H(+) for binding with Sc(3+) transport sites explained this trend within the pH range of 4.50 to 6.00, but not from pH 6.50-7.90. In this latter pH range, predicted fluxes were smaller than observed fluxes and this divergence increased with pH, from a factor of 4 to approximately 1000. Above pH 6.50, the calculated supply of Sc(3+) to the biointerface by physical diffusion of the free Sc(3+) ion and by the dissociation of its hydroxo-complexes (ScOH(2+), Sc(OH)2(+) and Sc(OH)3) was insufficient to support the high observed internalization fluxes. We speculate that this failure of the BLM could be due to the transmembrane transport of undissociated Sc hydroxo-complexes. Scandium uptake could be modeled reasonably well using a simple semiempirical equation considering equal contributions from Sc(3+), ScOH(2+), Sc(OH)2(+), and Sc(OH)3 and no H(+) competition. Our work highlights the importance of studying the possible role of hydroxo-species in trace metal uptake.

Influence of humic acid on algal uptake and toxicity of ionic silver.

The biogeochemical cycle of silver has been profoundly disturbed by various anthropogenic activities. To better understand the relationship among silver speciation, bioavailability, and toxicity in freshwaters, we have studied the short-term uptake of silver by two species of green algae, Chlamydomonas reinhardtii and Pseudokirchneriella subcapitata, in the presence or absence of a well-characterized humic acid (Suwannee River Humic Acid, SRHA). The free Ag(+) concentrations in the exposure solutions were determined using an equilibrium ion-exchange technique. According to the biotic ligand model, for a given free metal ion concentration, metal uptake should remain the same in the presence or absence of humic acid. However, short-term silver uptake in the presence of SRHA was greater than anticipated on the basis of free Ag(+) concentration. Subsequent determination of silver subcellular distribution revealed that significantly more silver was present in the "cell debris" fraction (known to contain the cell wall and fragmented membranes) in the presence of SRHA than in its absence. Finally, this increase in silver uptake in the presence of humic acid did not result in decreased algal growth. These results suggest that the increase in silver uptake observed in the presence of SRHA is surface-bound, not truly internalized.

Uptake and subcellular partitioning of trivalent metals in a green alga: comparison between Al and Sc.

Despite 40+ years of research on aluminum (Al) toxicity in aquatic organisms, Al transport mechanisms through biological membranes, and the intracellular fate of Al once assimilated, remain poorly understood. The trivalent metal scandium shares chemical similarities with Al and, unlike Al, it has a convenient radioactive tracer (Sc-46) allowing for relatively simple measurements at environmentally relevant concentrations. Thus, we investigated the potential of Sc to substitute for Al in uptake and intracellular fate studies with the green alga Chlamydomonas reinhardtii. Short-term (<60 min) competitive uptake experiments indicated that Al does not inhibit Sc influx, implying that these metals do not share a common transport mechanism. Also, internalized Al concentrations were ~4 times higher than Sc concentrations after long-term (72 h) exposures under similar conditions (4.5 µM AlT or ScT, 380 µM FT, pH 7.0, 3.8 pM Al calc (3+) and 1.0 pM Sc calc (3+) ). However, interesting similarities were observed in their relative subcellular distributions, suggesting possible common toxicity/tolerance mechanisms. Both metals mostly distributed to the organelles fraction and almost no association was found with the cytosolic proteins. The greatest difference was observed in the cellular debris fraction (membranes and nucleus) where Al was much more concentrated than Sc. However, it is not clear whether or not this fraction contained extracellular metal associated with the algal surface. To summarize, Sc does not seem to be an adequate substitute of Al for transport/uptake studies, but could be for investigations of toxicity/tolerance mechanisms in C. reinhardtii. Further work is needed to verify this latter suggestion.

Evolutionary change driven by metal exposure as revealed by coding SNP genome scan in wild yellow perch (Perca flavescens).

Pollution can drive rapid evolutionary change in wild populations. This study targets functional polymorphisms of chronically metal-contaminated wild yellow perch (Perca flavescens). A de novo transcriptome scan contrasted subsets of individuals from clean (n = 16) and contaminated (n = 16) lakes to identify 87 candidate annotated coding SNPs. Candidate genotypes and liver [metal] were obtained in 10 populations (n = 1,052) and a genome scan distinguished outliers: one nuclear (cyclin G1 gene) and two mitochondrial (cytochrome b and NADH dehydrogenase subunit 2 genes) also displaying allelic correlation to mean population [cadmium]. Whole mtDNA and 17 kb surrounding cyclin G1 were characterised through 454 sequencing thus revealing two non-synonymous substitutions involving dissimilar amino acids. Based on associated functions and inter-population differentiation, contaminated perch may have been selected for fast life cycle completion (p53 pathway) and memorization impairment mitigation (long-term potentiation pathway). In accordance with predicted evolutionary trajectory for stressed and energy deprived organisms, adapted perch would not compensate for repair mechanism inhibition, instead reallocating energy towards growth and favouring inexpensive impairment mitigation adaptations over costly detoxification. Overall, 85 years of selection could have driven rapid, potentially adaptive evolution by selecting alleles increasing perch fitness in polluted environments.

The Lumbosacral Fractional Curve in Adult Degenerative Scoliosis.

Spine surgeons are often faced with a profoundly difficult challenge in surgically treating adult degenerative scoliosis. Deformity correction surgery is complicated by the difficulty in offering extensive surgical corrections to the elderly, complication-prone population it commonly affects. As spine surgeons attempt to offer minimally invasive solutions to this disease process, the need for fusion of the fractional curve at L4, L5, and S1 may be discounted. A treatment strategy to identify, address, and treat the fractional curve with either open or minimally invasive techniques can lead to improved patient outcomes and decrease revision rates in this complicated pathologic process.

Extending the biotic ligand model to account for positive and negative feedback interactions between cadmium and zinc in a freshwater alga.

Low concentrations of essential trace metals such as zinc (Zn) were recently shown to strongly modulate cadmium (Cd) uptake in the freshwater alga Chlamydomonas reinhardtii. Here we studied the mechanisms of Cd and Zn acquisition by this alga, using metal uptake kinetics experiments. Cadmium uptake rates fitted a three transport site model characterized by the affinity constants K(Cd­1)(Cd) = 10(5.0), K(Cd­2)(Cd) = 10(7.6), and K(Cd­3)(Cd) = 10(8.8). Similar uptake kinetics were obtained for Zn with K(Zn­1)(Zn) = 10(5.0), K(Zn­2)(Zn) = 10(7.4), and K(Zn­3)(Zn) > 10(9). Competitive binding experiments suggest that Zn and Cd share the same three transport systems. The capacities of the transport systems were modulated by as much as 10-fold following preacclimation to high or low Zn(2+) and Cd(2+) concentrations. We conclude that the strong protective effect of Zn on Cd accumulation is mainly due to the reduction of the maximal uptake rate of the high-affinity Zn­2 (or Cd­2) transport system. A biotic ligand model was developed to incorporate the effects of both chemical speciation and physiological regulation of Cd transport systems. The model successfully predicts the experimentally measured steady-state Cd content of C. reinhardtii in the presence of low or high [Zn(2+)].