Sorption of hydrophobic organic contaminants and trace metals on phytoplankton and implications for toxicity assessment

The partitioning of trace metals and hydrophobic organic contaminants to phytoplankton determines their toxicity as well as their fate and transport in aquatic ecosystems. Accurate impact assessments, therefore, depend on a good understanding of the factors regulating the sorption of these compounds to biotic particles. The accumulation of chlorinated organic compounds in phytoplankton is generally considered as being due solely to physical sorption, described by reversible equilibrium models based on Langmuir or Freundlich isotherms. On the other hand, the uptake of trace metals is a two phase process: a fast sorption component viewed as an ionexchange or a covalent bonding process with cell surface ligands, followed by an intracellular transport phase that is dependent on cellular metabolic activity. The uptake of inorganic and hydrophobic organic pollutants and their bioaccumulation are influenced in a complex manner by duration of exposure and cell density, by environmental factors such as pH, the concentration of cations and of dissolved and colloidal organic matter, as well as by phytoplankton physiological condition. High concentrations of H⁺, Ca²⁺, and Mg²⁺ ions will reduce trace metal sorption by directly competing for uptake sites on the cell's surface, whereas the presence of dissolved organic carbon such as natural and synthetic chelators and phytoplankton exudates will reduce the bioavailability of both trace metals and hydrophobic organic contaminants. Thus, the impact of toxic contaminants on phytoplankton may be determined as much by the factors influencing uptake and partitioning as by the potency of the toxicants and interspecies differences in sensitivity. Recommendations for improving toxicity assessments are presented.     

COMPARATIVE KINETIC STUDIES OF NITRATE-LIMITED GROWTH AND NITRATE UPTAKE IN PHYTOPLANKTON IN CONTINUOUS CULTURE1

A comparative study of nitrate-limited growth and nitrate uptake was carried out in chemostat cultures of Ankistrodesmus falcatus (Corda) Ralfs., Asterionella formosa Hass., and Fragilaria crotonensis Kit. In each species growth rate (μ) was related to total cell nitrogen or cell quota (q) by the empirical Droop growth function. Nitrate uptake was a function of both external N concentration and q. The apparent maximum uptake rate (V_m') at a given μ was inversely related to q – q₀, where q₀ is the minimum quota. The apparent half-saturation constant for uptake, (K_m') appears to show a slight inverse trend with μ, although statistical analysis shows that this trend is inconclusive. When q approaches q₀, V_m' is several orders of magnitude greater than μq, the calculated steady-state uptake rate. As q increases, however, the difference between these two variables decreases sharply until q approaches q_m, the cell quota for nitrogen-rich cells. At this point the difference between μq and V_m' disappears. This behavior is explained by the feedback regulation of N uptake. The inverse relationship between V_m' and q – q₀ can be described by an empirical three-parameter equation.     

OPTIMUM N:P RATIOS AND COEXISTENCE OF PLANKTONIC ALGAE1

The optimum atomic ratio of N to P, the ratio at which one nutrient limitation changes over to the other, was determined in seven species of freshwater planktonic algae. The ratio varied over a wide range among species; the average for these species was 17. If the cellular nutrient ratios in marine species are comparable with those in freshwater organisms, Redfield's ratio of 15 is remarkably close to the average. Cellular N:P ratios varied over a 24-h period under a light:dark cycle. The variation of the optimum ratio between species and diel change in cellular N:P ratios within a species could play an important role in population dynamics by enhancing the probability of coexistence of species.     

Inhibition of Ouabain-binding to (Na+ + K+)ATPase by antibody against the catalytic subunit but not by antibody against the glycoprotein subunit

Antibodies against purified ($\text{Na}{}^{\mathrm{+}}\text{+}\text{K}{}^{\mathrm{+}}\text{)}\text{ATPase}$ from the rectal gland of Squalus acanthias, as well as against its catalytic subunit, inhibited ouabain binding by as much as 50%. However, antibodies against the glycoprotein subunit did not inhibit ouabain binding. These data suggest that binding of antibody against the catalytic subunit to the enzyme either covers the ouabain binding site or destroys its conformation, while binding of antibody against the glycoprotein has no such effect.     

Determination of adenosine 5'-triphosphate by the luciferase system with a stopped-flow spectrometer.

A stopped-flow spectrometer is used for ATP assay by firefly luciferase-luciferin method. It allows one to record initial rise of the light intensity and to differentiate the light produced due to the conversion of ADP to ATP by nucleoside diphosphokinase in the firefly lantern when other nucleoside triphosphates are present. Addition of luciferin (0.27 mm) to luciferase extract increases the light intensity by a factor of 50–100. This method can be used to measure ATP in the picomole range.     

Control of the pericentrosomal H2O2 level by peroxiredoxin I is critical for mitotic progression

Proteins associated with the centrosome play key roles in mitotic progression in mammalian cells. The activity of Cdk1-opposing phosphatases at the centrosome must be inhibited during early mitosis to prevent premature dephosphorylation of Cdh1—an activator of the ubiquitin ligase anaphase-promoting complex/cyclosome—and the consequent premature degradation of mitotic activators. In this paper, we show that reversible oxidative inactivation of centrosome-bound protein phosphatases such as Cdc14B by H₂O₂ is likely responsible for this inhibition. The intracellular concentration of H₂O₂ increases as the cell cycle progresses. Whereas the centrosome is shielded from H₂O₂ through its association with the H₂O₂-eliminating enzyme peroxiredoxin I (PrxI) during interphase, the centrosome-associated PrxI is selectively inactivated through phosphorylation by Cdk1 during early mitosis, thereby exposing the centrosome to H₂O₂ and facilitating inactivation of centrosome-bound phosphatases. Dephosphorylation of PrxI by okadaic acid–sensitive phosphatases during late mitosis again shields the centrosome from H₂O₂ and thereby allows the reactivation of Cdk1-opposing phosphatases at the organelle.     

The growth-inhibitory effects of pawpaw (Asimina triloba [L.] Dunal) roots,twigs, leaves,and fruit against human gastric (AGS) and cervical (HeLa) cancer cells and their anti-inflammatory activities

Molecular Biology Reports - The pawpaw tree has several beneficial effects. However, no studies have been conducted to address the mechanisms underlying the cytotoxic effects of pawpaw extracts...     

Genomic analysis of facultatively oligotrophic haloarchaea of the genera Halarchaeum,Halorubrum, and Halolamina,isolated from solar salt

Archives of Microbiology - Extremely halophilic archaea (haloarchaea) belonging to the phylum Euryarchaeota have been found in high-salinity environments. In this study, Halarchaeum sp. CBA1220,...     

Application of Biofilm-Forming Bacteria on the Enhancement of Organophosphorus Fungicide Degradation

This study aimed to develop technology enhancing the biodegradation efficacy against organophosphorus fungicide with biofilm-forming bacteria in situ. Using the crystal violet staining method, two bacterial strains having biofilm formation capability were isolated and identified as Pseudomonas sp. C7 and Bacillus sp. E5. Compared with the culture of tolclofos-methyl degrader Sphingomonas sp. 224, biofilm formation was improved by co-inoculation with biofilm-forming bacterium Bacillus sp. E5. Evaluated in liquid culture conditions, this two-species mixed consortium was observed to degrade tolclofos-methyl more effectively than Sphingomonas sp. 224 alone, with an approximately 90% degradation efficiency within 48 h of dosing. The improved effectiveness of the consortium biofilm was reflected using soil in situ with an approximately 7% increased degradation ratio over Sphingomonas sp. 224 alone. This is the first report demonstrating improved bioremediation degradation efficacy against tolclofos-methyl exhibited by a consortium biofilm. This work presents a possible effective bioremediation strategy using a specific biofilm composition against pollutants containing organophosphorus compounds in situ.