Managing vegetation in surface-flow wastewater-treatment wetlands for optimal treatment performance

Constructed wetlands that mimic natural marshes have been used as low-cost alternatives to conventional secondary or tertiary wastewater treatment in the U.S. for at least 30 years. However, the general level of understanding of internal treatment processes and their relation to vegetation and habitat quality has not grown in proportion to the popularity of these systems. We have studied internal processes in surface-flow constructed wastewater-treatment wetlands throughout the southwestern U.S. since 1990. At any given time, the water quality, hydraulics, water temperature, soil chemistry, available oxygen, microbial communities, macroinvertebrates, and vegetation each greatly affect the treatment capabilities of the wetland. Inside the wetland, each of these components plays a functional role and the treatment outcome depends upon how the various components interact. Vegetation plays a uniquely important role in water treatment due to the large number of functions it supports, particularly with regard to nitrogen transformations. However, it has been our experience that vegetation management is critical for achieving and sustaining optimal treatment function. Effective water treatment function and good wildlife quality within a surface-flow constructed wetland depend upon the health and sustainability of the vegetation. We suggest that an effective tool to manage and sustain healthy vegetation is the use of hummocks, which are shallow emergent plant beds within the wetland, positioned perpendicular to the water flow path and surrounded by water sufficiently deep to limit further emergent vegetation expansion. In this paper, we describe the use of a hummock configuration, in conjunction with seasonal water level fluctuations, to manage the vegetation and maintain the treatment function of wastewater-treatment wetlands on a sustainable basis.     

An Investigation of Freezing of Supercooled Water on Anti-Freeze Protein Modified Surfaces

This work investigates how functionalization of aluminium surfaces with natural type III Anti-Freeze Protein (AFP) affects the mechanism of heterogeneous ice nucleation. First the bulk ice nucleation properties of distilled water and aqueous solution of AFP were evaluated by differential scanning calorimetry. Then the modified surface was characterized by Secondary Ions Mass Spectroscopy (SIMS), Fourier Transform InfraRed (FTIR) spectroscopy and contact angle measurement. Freezing experiments were then conducted in which water droplets underwent a slow controlled cooling. This study shows that compared to uncoated aluminium, the anti-freeze proteins functionalized surfaces exhibit a higher and narrower range of freezing temperature. It was found that these proteins that keep living organisms from freezing in cold environment act in the opposite way once immobilized on surfaces by promoting ice nucleation. Some suggestions regarding the mechanism of action of the observed phenomena were proposed based on the Classical Nucleation Theory (CNT).     

Formulation of a coupled mechanism between solute diffusion,phosphatase-kinase reactions and membrane potentials for the primary active transport of phosphorylated substrates through biological membranes

Coupled interrelations occurring between a phosphatase/kinase reaction sequence acting in unstirred layers and on both sides of a charged biomembrane pore structure are presented as a plausible kinetic model for the primary active transport of phosphorylated molecules. Simulations conducted at the cell level and with credible numerical values demonstrate that the enzymes positions strongly regulate the membrane permeability for the transported substrate. Depending on both the enzymes positions (more or less far from the membrane) and the membrane charges, the membrane may appear either impervious, either permeable or able to actively transport a phosphorylated substrate. Globally all happens as if, in function of the enzymes positions, a permanent pore may be regulated, changing from a more closed to a more open conformation.     

Identification of amino acid residues critical for the B cell growth-promoting activity of HIV-1 matrix protein p17 variants

Background

HIV-1 matrix protein p17 variants (vp17s) detected in HIV-1-infected patients with non-Hodgkin's lymphoma (HIV-NHL) display, differently from the wild-type protein (refp17), B cell growth-promoting activity. Biophysical analysis revealed that vp17s are destabilized as compared to refp17, motivating us to explore structure-function relationships.

Stabilization of the Tertiary Structure of the Cholera Toxin A1 Subunit Inhibits Toxin Dislocation and Cellular Intoxication

Cholera toxin (CT) moves from the cell surface to the endoplasmic reticulum (ER) by retrograde vesicular transport. The catalytic subunit of CT (CTA1) then crosses the ER membrane and enters the cytosol in a process that involves the quality control mechanism of ER-associated degradation. The molecular details of this dislocation event have not been fully characterized. Here, we report that thermal instability in the CTA1 subunit—specifically, the loss of CTA1 tertiary structure at 37 °C—triggers toxin dislocation. Biophysical studies found that glycerol preferentially stabilized the tertiary structure of CTA1 without having any noticeable effect on the thermal stability of its secondary structure. The thermal disordering of CTA1 tertiary structure normally preceded the perturbation of its secondary structure, but in the presence of 10% glycerol the temperature-induced loss of CTA1 tertiary structure occurred at higher temperatures in tandem with the loss of CTA1 secondary structure. The glycerol-induced stabilization of CTA1 tertiary structure blocked CTA1 dislocation from the ER and instead promoted CTA1 secretion into the extracellular medium. This, in turn, inhibited CT intoxication. Glycerol treatment also inhibited the in vitro degradation of CTA1 by the core 20S proteasome. Collectively, these findings indicate that toxin thermal instability plays a key role in the intoxication process. They also suggest the stabilization of CTA1 tertiary structure is a potential goal for novel antitoxin therapeutic agents.     

Stability in -species coevolutionary systems

Stability criteria have recently been developed for coevolutionary Lotka–Volterra systems where individual fitness functions are assumed to be linear in the population state. We extend these criteria as part of a general theory of coevolution (that combines effects of ecology and evolution) based on arbitrary (i.e. nonlinear) fitness functions and a finite number of individual phenotypes. The central role of the stationary density surface where species’ densities are at equilibrium is emphasized. In particular, for monomorphic resident systems, it is shown coevolutionary stability is equivalent to ecological stability combined with evolutionary stability on the stationary density surface. Also discussed is how our theory relates to recent treatments of phenotypic coevolution via adaptive dynamics when there is a continuum of individual phenotypes.