Fungal Bioweathering of Mimetite and a General Geomycological Model for Lead Apatite Mineral Biotransformations

Fungi play important roles in biogeochemical processes such as organic matter decomposition, bioweathering of minerals and rocks, and metal transformations and therefore influence elemental cycles for essential and potentially toxic elements, e.g., P, S, Pb, and As. Arsenic is a potentially toxic metalloid for most organisms and naturally occurs in trace quantities in soil, rocks, water, air, and living organisms. Among more than 300 arsenic minerals occurring in nature, mimetite [Pb₅(AsO₄)₃Cl] is the most stable lead arsenate and holds considerable promise in metal stabilization for in situ and ex situ sequestration and remediation through precipitation, as do other insoluble lead apatites, such as pyromorphite [Pb₅(PO₄)₃Cl] and vanadinite [Pb₅(VO₄)₃Cl]. Despite the insolubility of mimetite, the organic acid-producing soil fungus Aspergillus niger was able to solubilize mimetite with simultaneous precipitation of lead oxalate as a new mycogenic biomineral. Since fungal biotransformation of both pyromorphite and vanadinite has been previously documented, a new biogeochemical model for the biogenic transformation of lead apatites (mimetite, pyromorphite, and vanadinite) by fungi is hypothesized in this study by application of geochemical modeling together with experimental data. The models closely agreed with experimental data and provided accurate simulation of As and Pb complexation and biomineral formation dependent on, e.g., pH, cation-anion composition, and concentration. A general pattern for fungal biotransformation of lead apatite minerals is proposed, proving new understanding of ecological implications of the biogeochemical cycling of component elements as well as industrial applications in metal stabilization, bioremediation, and biorecovery.     

The activity of signal crayfish (Pacifastacus leniusculus) in relation to thermal and hydraulic dynamics of an alluvial stream, UK

Signal crayfish (Pacifastacus leniusculus) are an invasive species of global significance because of their detrimental impacts on freshwater environments and native organisms. The movement of signal crayfish was continuously monitored for 150-days through a 20-m reach of an alluvial stream in the UK. Passive integrated transponder-tags were attached to crayfish, allowing their location to be monitored relative to 16 antennae which were buried beneath the river bed. The activity of crayfish was related to water depth and temperature, which were continuously monitored within the instrumented reach. Crayfish were highly nocturnal, with less than 6% of movements recorded during daylight hours. Activity declined from September and was minimal in November when water temperature was low and flow depth was high. However, relations between environmental parameters and crayfish activity had poor explanatory power which may partly reflect biological processes not accounted for in this study. Water depth and temperature had a limiting relationship with crayfish activity, quantified using quantile regression. The results extend existing data on signal crayfish nocturnalism and demonstrate that, although signal crayfish can tolerate a range of flows, activity becomes limited as water temperature declines seasonally and when water depth remains high in autumn and winter months.     

Inhibition of acid production in Streptococcus mutans R9: Inhibition constants and reversibility

Abstract The pac gene encoding the penicillin G acylase (PGA) of Bacillus megaterium ATCC 14945 has been cloned in Escherichia coli HB101 ( proA, leuB ) using a selective minimal medium containing phenylacetyl-L-leucine instead of L-leucine. The nucleotide sequence of this gene has been determined and contains an open reading frame of 2406 nucleotides. The deduced amino acid sequence shows significant similarity with other β-lactam acylases. Although the PGA of B. megaterium is extracellular, the enzyme produced in E. coli appears to have a cytoplasmic localization.     

Time-Lapse Confocal Imaging of Calcium Dynamics in Starfish Embryos

During fertilization and cleavage, embryos undergo transient rises in their intracellular free calcium levels that are postulated to provide essential signals enabling normal development to proceed. In order to analyze the spatiotemporal patterns and possible biological significance of these calcium transients, time-lapse confocal microscopy was used to monitor starfish embryos during normal development and following experimental manipulations that disrupted cleavage and/or the release of calcium ions from internal stores in the embryo. For such analyses, oocytes were co-injected with dextran-conjugated forms of the calcium-sensitive fluorochrome calcium green (CG) and the calcium-insensitive dye rhodamine (Rh) for dual-channel confocal ratioing. Based on CG/Rh ratioed images obtained every 15 sec far the first few hours of development, no prominent calcium spikes were typically evident at the onset of the first cell cycle as hormone-treated oocytes resumed maturation and underwent germinal vesicle breakdown (GVBD). Subsequently, fertilizations of post-GVBD oocytes caused a single prolonged calcium wave that reached relatively uniform amplitudes throughout the ooplasm. Within 90 min after fertilization, most starfish zygotes began to display clusters of repetitive calcium oscillations that typically—but not invariably—preceded nuclear envelope breakdown, anaphase onset, and the formation of the first cleavage furrow. Rapidly decaying calcium oscillations continued through at least the first five cleavages in specimens that developed into normal blastulae, and unlike fertilization-induced calcium waves, such spikes tended to be more pronounced in the cortical cytoplasm during early cleavages. Thus, three different types of calcium dynamics—no marked transients, a single nonoscillating wave, and repetitive oscillations—were observed as normally developing starfish underwent prefertilization maturation, fertilization, and cleavage, respectively, suggesting that the spatiotemporal patterns of calcium spiking can change during starfish early development. In specimens microinjected with colchicine, calcium transients were also visible in the absence of cell divisions, indicating that calcium spiking can be uncoupled from cytokinesis. To assess whether calcium fluxes are required for normal development, oocytes were also treated with haparia to black calcium release mediated by inositol 1,4,5-trisphosphate (IP₃). Injections of heparin, but not the control molecule de-N-sulfated heparin, caused abnormal fertilization-induced calcium dynamics in a does-dependent fashion and typically abolished marked postfertilization calcium oscillations and normal cleavage. Based on correlative studies using caged IP₃, heparin interfered with IP₃-mediated calcium release, suggesting that such release is involved in the production of the free calcium elevations that occur in normally developing starfish embryos.     

Computational analysis of pediatric ventricular assist device implantation to decrease cerebral particulate embolization

Stroke is the most devastating complication after ventricular assist device (VAD) implantation with a 19% incidence and 65% mortality in the pediatric population. Current pediatric VAD technology and anticoagulation strategies alone are suboptimal. VAD implantation assisted by computational methods (CFD) may contribute reducing the risk of cerebral embolization. Representative three-dimensional aortic arch models of an infant and a child were generated. An 8 mm VAD outflow-graft (VAD-OG) anastomosed to the aorta was rendered and CFD was applied to study blood flow patterns. Particle tracks, originating in the VAD, were computed with a Lagrangian phase model and the percentage of particles entering the cerebral vessels was calculated. Eight implantation configurations (infant = 5 and child = 3) and 5 particle sizes (0.5, 1, 2, 3, and 4 mm) were considered. For the infant model, percentage of particles entering the cerebral vessels ranged from 15% for a VAD-OG anastomosed at 90° to the aorta, to 31% for 30° VAD-OG anastomosis (overall percentages: X² = 10,852, p < 0.0001). For the child model, cerebral embolization ranged from 9% for the 30° VAD-OG anastomosis to 15% for the 60° anastomosis (overall percentages: χ² = 10,323, p < 0.0001). Using detailed CFD calculations, we demonstrate that the risk of stroke depends significantly on the VAD implantation geometry. In turn, the risk probably depends on patient-specific anatomy. CFD can be used to optimize VAD implantation geometry to minimize stroke risk.     

Polar lipids of 'Pseudomonas diazotrophicus'

Abstract Reference strains of ' Pseudomonas diazotrophicus ' produce a range of polar lipids atypical of authentic Pseudomonas species. In addition to the phospholipids common in Gram-negative bacteria (phosphatidylglycerol, diphosphatidylglycerol, and phosphatidylethanolamine), N -methylated derivatives of phosphatidylethanolamine (including phosphatidylcholine) and an ornithine amide lipid are also present. The preponderant ester-bound fatty acid (up to 80% of the total) is cis -vaccenic acid ( cis -octadec-11-enoic acid), while 3-hydroxyoctadecanoic acid is the major amide-bound fatty acid in the ornithine lipid. Possible implications of the data for classification of the organism are discussed.