Episodic bioavailability of environmental mercury: implications for biotechnological control of mercury pollution

Perennial wildfires in Africa and other continents contribute an estimated 8 x 105 kg of mercury to the global atmosphere with a residence time of approximately one year. This phenomenon changes the flux of biologically available mercury in natural microbial communities where enzymatic actions, including mercuric reductase and organomercurial lyase activities, underpin the biogeochemical cycling of mercury with repercussions for human exposure to toxic forms of the element. To elucidate the impact of episodic mercury bioavailability on the response of microbial communities, the expression of microbial proteins and nucleic acids in environmental strains of Pseudomonas species were evaluated under various concentrations of mercury ranging from 0 to 500 µM. Routine cultivation of Pseudomonas aeruginosa PU21 containing the 142.5 kb plasmid Rip64 in medium containing 100 µg of Hg++/ml (500 µM) exhibited a prolonged lag phase survived by hyper-resistant cells able to grow in medium containing 200 µg of Hg++/ml. Nucleic acid analyses showed a distinct mutation in the merA gene encoding for mercuric reductase activity in cells able to grow at elevated mercury concentrations. A similar mutation was detected in the merR locus which serves as the regulator of the mer operon. Mutations were not detected in merC which encodes for a hydrophobic membrane-associated protein implicated in active mercury transport. Protein profiles of cells grown with elevated mercury concentrations were associated with a stable increase in the production of specific polypeptides. In addition, the survival and genetic response of naturally-occurring mercury resistant bacteria inoculated into contaminated environmental samples were monitored in microcosm experiments over a 30 day period. The results suggest that sudden exposure to high concentrations of mercury either decimates the bacterial population or selects for hyper-resistant strains with high level of constitutive expression of active proteins, including mercuric reductase. Methyl mercury was observed to cause a higher level of induction for mercuric reductase than the specific substrate, inorganic mercury. The selection of hyper-resistant strains is potentially useful for biotechnological strategies to control the bioavailability of mercury, and thereby potentially reducing the re-uptake of mercury into vegetation in regions frequently subjected to wildfires. (African Journal of Biotechnology: 2002 1(1): 1-9

Effects of candesartan versus amlodipine on capillary rarefaction, pulse wave velocity, and central blood pressure in patients with essential hypertension

Background: A reduction in the density of capillaries (rarefaction) is known to occur in many tissues in patients with essential hypertension and play a role in increasing Blood Pressure (BP). The aim of this trial was to assess in a randomized, double blind, design the effects of treatment of hypertension with candesartan versus amlodipine on microvascular rarefaction and other indices of vascular function. Methods: We recruited twenty-two individuals with mild-to-moderate hypertension. After a 2-week placebo run-in period, patients who remained hypertensive (≥140/90 mmHg) were randomized to 8-weeks treatment with Candesartan tablets 8mg daily (with forced titration to 16mg) or Amlodipine tablets 5mg daily (with forced titration to 10mg). The capillary microcirculation was studied using CapiScope system CAM1. Pulse wave velocity, central BP and aortic Augmentation Index were also measured. Results: We observed significant reductions in brachial BP, and central BP after 4 and 8 weeks treatment with either candesartan or amlodipine but there was no significant effect on basal (functional) or maximal (structural) capillary densities, or pulse wave velocity. Conclusion: Eight weeks treatment of hypertension with either amlodipine or candesartan significantly reduced brachial and central BP but was not sufficient to induce a regression in functional or structural microvascular abnormalities

Transduction of linked chromosomal genes between Pseudomonas aeruginosa strains during incubation in situ in a freshwater habitat

Both transduction of single chromosomal loci and cotransduction of closely linked loci were observed between lysogenic and nonlysogenic strains of Pseudomonas aeruginosa in a freshwater habitat. Transductants were recovered at frequencies of 10-6 to 10-5 transductants per CFU. Transductants of lysogenized strains were recovered 10- to 100-fold more frequently than were transductants of nonlysogenic parents. Lysogens are thus capable of introducing phages which mediate generalized transduction into the natural microbial community and serving as recipients of transduced DNA. It would appear that lysogeny has the potential of increasing the size and flexibility of the gene pool available to natural populations of bacteria. The ability to generate and select new genetic combinations through phage-mediated exchange can be significant in the face of a continually changing environment and may contribute to the apparent fitness of the lysogenic state in natural ecosystems.Peer reviewedMicrobiology and Molecular Genetic

Ecological Complex Systems

Main aim of this topical issue is to report recent advances in noisy nonequilibrium processes useful to describe the dynamics of ecological systems and to address the mechanisms of spatio-temporal pattern formation in ecology both from the experimental and theoretical points of view. This is in order to understand the dynamical behaviour of ecological complex systems through the interplay between nonlinearity, noise, random and periodic environmental interactions. Discovering the microscopic rules and the local interactions which lead to the emergence of specific global patterns or global dynamical behaviour and the noises role in the nonlinear dynamics is an important, key aspect to understand and then to model ecological complex systems.Comment: 13 pages, Editorial of a topical issue on Ecological Complex System to appear in EPJ B, Vol. 65 (2008

Continuous culture model to examine factors that affect transduction among Pseudomonas aeruginosa strains in freshwater environments

Transduction among Pseudomonas aeruginosa strains was observed in continuous cultures operated under environmentally relevant generation times, cell densities, and phage-to-bacterium ratios, suggesting its importance as a natural mechanism of gene transfer. Transduction was quantified by the transfer of the Tra(sup-) Mob(sup-) plasmid Rms149 from a plasmid-bearing strain to an F116 lysogen that served as both the recipient and source of transducing phages. In control experiments in which transduction was prevented, there was a reduction in the phenotype of the mock transductant over time. However, in experiments in which transduction was permitted, the proportion of transductants in the population increased over time. These data suggest that transduction can maintain a phenotype for an extended period of time in a population from which it would otherwise be lost. Changes in the numbers of transductants were analyzed by a two-part mathematical model, which consisted of terms for the selection of the transductant's phenotype and for the formation of new transductants. Transduction rates ranged from 10(sup-9) to 10(sup-6) per total viable cell count per ml per generation and increased with both the recipient concentration and the phage-to-bacterium ratio. These observations indicate an increased opportunity for transduction to occur when the interacting components are in greater abundance.Peer reviewedMicrobiology and Molecular Genetic

“Control-Alt-Delete”: Rebooting Solutions for the E-Waste Problem

A number of efforts have been launched to solve the global electronic waste (e-waste) problem. The efficiency of e-waste recycling is subject to variable national legislation, technical capacity, consumer participation, and even detoxification. E-waste management activities result in procedural irregularities and risk disparities across national boundaries. We review these variables to reveal opportunities for research and policy to reduce the risks from accumulating e-waste and ineffective recycling. Full regulation and consumer participation should be controlled and reinforced to improve local e-waste system. Aiming at standardizing best practice, we alter and identify modular recycling process and infrastructure in eco-industrial parks that will be expectantly effective in countries and regions to handle the similar e-waste stream. Toxicity can be deleted through material substitution and detoxification during the life cycle of electronics. Based on the idea of "Control-Alt-Delete", four patterns of the way forward for global e-waste recycling are proposed to meet a variety of local situations