Using SPMDs to Assess Natural Recovery of PCB-contaminated Sediments in Lake Hartwell,SC: I. A Field Test of New In-Situ Deployment Methods

Results from the field testing of some innovative sampling methods developed to evaluate risk management strategies for polychlorinated biphenyl (PCB) contaminated sediments are presented. Semipermeable membrane devices (SPMDs) were combined with novel deployment methods to quantify the availability of PCBs at the Sangamo-Weston Lake Hartwell Superfund Site in SC. Three locations in Lake Hartwell were examined: a background site (BKG) with little detectable contamination and two contaminated sites (T-M/N and T-O). PCB availability was quantified using sediment surface samplers designed to hold SPMDs in contact with surface sediments, benthic dome samplers designed to enclose and suspend SPMDs at the sediment-water interface, and commercially obtained SPMD cages suspended in the water column. A two-way analysis of variance showed significant effects by sampler type (P < 0.0001) and site (P < 0.0001) for mean time-weighted average (TWA) total PCBs (t-PCBs). Regardless of the SPMD sampler used, mean TWA t-PCBs were directly proportional to the level of contamination present (BKG < T-M/N < T-O). Water column and surface sediment sampler t-PCB uptake patterns were described by a significant linear fit of the data (r² = 0.9625, p < 0.0001, and r² = 0.8188, p < 0.0001, respectively). Dome and sediment surface SPMD samples had a higher percentage of higher chlorinated PCBs compared to water column samples.     

Inhibition by zinc of the binding of C1 to antigen-antibody complexes

Zinc sulphate in the range of 10^?4 to 2×10^?5 M prevents the binding of $\text{C}\text{1}$ to antigen antibody complexes, and the initation of the cascade of events in the classical complement pathway leading to cell lysis. Other heavy metals, Co⁺⁺, Cd⁺⁺, Cu⁺⁺, or Mn⁺⁺ were without effect in this concentration range. Zinc was ineffective when added after $\text{C}\text{1}$ was bound and failed to displace $\text{C}\text{1}$ which was already bound to antigen antibody complexes. The ability of zinc to regulate the binding of the zymogen or activated form of $\text{C}\text{1}$ to antigen-antibody complexes represents a new method of controlling the initiation of the classical complement pathway.     

Rhipicephalus (Boophilus) microplus: distinct acute phase proteins vary during infestations according to the genetic composition of the bovine hosts, Bos taurus and Bos indicus

Tick bites may trigger acute phase responses. Positive and negative acute phase proteins were measured in infested cattle genetically resistant and susceptible to ticks. During heavier infestations levels of haptoglobin increased significantly in susceptible bovines; levels of serum amyloid A increased in resistant bovines; levels of alpha-1-acid glycoprotein decreased significantly in resistant bovines; levels of transferrin decreased significantly in susceptible bovines. In conclusion, tick infestations trigger acute phase responses and enhancement of specific acute phase proteins differs according to the genetic composition of hosts. Acute phase proteins may constitute useful biological signatures for monitoring the stress induced by tick infestations.     

Changes of enzyme activity in lipid signaling pathways related to substrate reordering

The static fluid mosaic model of biological membranes has been progressively complemented by a dynamic membrane model that includes phospholipid reordering in domains that are proposed to extend from nanometers to microns. Kinetic models for lipolytic enzymes have only been developed for homogeneous lipid phases. In this work, we develop a generalization of the well-known surface dilution kinetic theory to cases where, in a same lipid phase, both domain and nondomain phases coexist. Our model also allows understanding the changes in enzymatic activity due to a decrease of free substrate concentration when domains are induced by peptides. This lipid reordering and domain dynamics can affect the activity of lipolytic enzymes, and can provide a simple explanation for how basic peptides, with a strong direct interaction with acidic phospholipids (such as beta-amyloid peptide), may cause a complex modulation of the activities of many important enzymes in lipid signaling pathways.     

Lovastatin biosynthesis by Aspergillus terreus with the simultaneous use of lactose and glycerol in a discontinuous fed-batch culture

The influence of various combinations of glycerol and lactose feed on the biosynthesis of two polyketide metabolites, lovastatin and (+)-geodin, by Aspergillus terreus ATCC20542 in a discontinuous fed-batch culture was presented. In these experiments lactose and/or glycerol were also used as the initial carbon substrates in the cultivation media. The application of glycerol feed, when lactose is the initial substrate, leads to the appreciable lovastatin concentration in the broth (122.4 mg l⁻¹), nevertheless the abundant (+)-geodin level is at the same time obtained (255.5 mg l⁻¹). The cultures with glycerol as the initial substrate and fed with lactose produce less lovastatin and (+)-geodin. The application of the various combined glycerol and/or lactose feeds allows for improving lovastatin production up to 161.8 mg l⁻¹ and decreases (+)-geodin concentration to 98.7 mg l⁻¹. The analysis of product formation rates and yield coefficients indicates that lovastatin is more efficiently produced on lactose, especially in the initial stages of the cultivation. Glycerol efficiently sustains fungal activity to form these polyketides in the late idiophase but it mainly favours (+)-geodin formation, if solely used in the feed. The feeds performed both with lactose and glycerol occur to be the most desired to maximise lovastatin and minimise (+)-geodin formation.     

Effects of precipitation on photosynthesis and water potential in Andropogon gerardii and Schizachyrium scoparium in a southern mixed grass prairie

In grassland ecosystems, spatial and temporal variability in precipitation is a key driver of species distributions and population dynamics. We experimentally manipulated precipitation to understand the physiological basis for differences in responses of species to water availability in a southern mixed grass prairie. We focused on the performance of two dominant C₄ grasses, Andropogon gerardii Vitman and Schizachyrium scoparium (Michx.) Nash, in treatments that received ambient rainfall, half of ambient rainfall (“drought” treatment), or approximately double ambient rainfall (“irrigated” treatment). Water potentials of S. scoparium were lower than A. gerardii, suggesting superior ability to adjust to water deficit in S. scoparium. Additionally, drought reduced photosynthesis to a greater extent in A. gerardii compared to S. scoparium. Leaf-level photosynthesis rates were similar in ambient and irrigated treatments, but were significantly lower in the drought treatment. Although stomatal conductance was reduced by drought, this was not limiting for photosynthesis. Leaf δ¹³C values were decreased by drought, caused by an increase in C_i/C_a. Chlorophyll fluorescence measures indicated light-harvesting rates were highest in irrigated treatments, and were lower in ambient and drought treatments. Moreover, drought resulted in a greater proportion of absorbed photon energy being lost via thermal pathways. Reductions in photosynthesis came as a result of non-stomatal limitations in the C₄ cycle. Our results provide mechanistic support for the hypothesis that S. scoparium is more drought tolerant than A. gerardii.     

Patterning, prestress, and peeling dynamics of myocytes

As typical anchorage-dependent cells myocytes must balance contractility against adequate adhesion. Skeletal myotubes grown as isolated strips from myoblasts on micropatterned glass exhibited spontaneous peeling after one end of the myotube was mechanically detached. Such results indicate the development of a prestress in the cells. To assess this prestress and study the dynamic adhesion strength of single myocytes, the shear stress of fluid aspirated into a large-bore micropipette was then used to forcibly peel myotubes. The velocity at which cells peeled from the surface, V(peel), was measured as a continuously increasing function of the imposed tension, T(peel), which ranges from approximately 0 to 50 nN/ micro m. For each cell, peeling proved highly heterogeneous, with V(peel) fluctuating between 0 micro m/s ( approximately 80% of time) and approximately 10 micro m/s. Parallel studies of smooth muscle cells expressing GFP-paxillin also exhibited a discontinuous peeling in which focal adhesions fractured above sites of strong attachment (when pressure peeled using a small-bore pipette). The peeling approaches described here lend insight into the contractile-adhesion balance and can be used to study the real-time dynamics of stressed adhesions through both physical detection and the use of GFP markers; the methods should prove useful in comparing normal versus dystrophic muscle cells.