Stoichiometry and kinetics of mercury uptake by photosynthetic bacteria

Mercury adsorption on the cell surface and intracellular uptake by bacteria represent the key first step in the production and accumulation of highly toxic mercury in living organisms. In this work, the biophysical characteristics of mercury bioaccumulation are studied in intact cells of photosynthetic bacteria by use of analytical (dithizone) assay and physiological photosynthetic markers (pigment content, fluorescence induction, and membrane potential) to determine the amount of mercury ions bound to the cell surface and taken up by the cell. It is shown that the Hg(II) uptake mechanism (1) has two kinetically distinguishable components, (2) includes co-opted influx through heavy metal transporters since the slow component is inhibited by Ca2+ channel blockers, (3) shows complex pH dependence demonstrating the competition of ligand binding of Hg(II) ions with H+ ions (low pH) and high tendency of complex formation of Hg(II) with hydroxyl ions (high pH), and (4) is not a passive but an energy-dependent process as evidenced by light activation and inhibition by protonophore. Photosynthetic bacteria can accumulate Hg(II) in amounts much (about 105) greater than their own masses by well-defined strong and weak binding sites with equilibrium binding constants in the range of 1 (muM)-1 and 1 (mM)-1, respectively. The strong binding sites are attributed to sulfhydryl groups as the uptake is blocked by use of sulfhydryl modifying agents and their number is much (two orders of magnitude) smaller than the number of weak binding sites. Biofilms developed by some bacteria (e.g., Rvx. gelatinosus) increase the mercury binding capacity further by a factor of about five. Photosynthetic bacteria in the light act as a sponge of Hg(II) and can be potentially used for biomonitoring and bioremediation of mercury-contaminated aqueous cultures

Effect of azotobacter products on lettuce transplants

While the nutrient supply in conventional farming is mainly provided by fertilizers, the organic farmers have to use nutrient-rich organic materials to produce seedlings of high quality. The advantage of transplants use in the vegetable growing can be to realize earliness (it gives higher benefit), increase growth safety, etc. Effect of bacteria (like microbial agent) can transform faster the nutrients from organic material. It can give opportunity for organic manure to affect faster in the substrate. The aim of this research was to determine: growing lettuce seedling only with the use of organic materials, estimating the effectiveness of some microbial products in vegetable transplant growing, and effect of microbial products on efficiency of manures. The results show that the combination of organic fertilizers and soil bacteria has effect on the increasing of nitrogen up-take of plants

Capacity and kinetics of light-induced cytochrome oxidation in intact cells of photosynthetic bacteria

Light-induced oxidation of the reaction center dimer and periplasmic cytochromes was detected by fast kinetic difference absorption changes in intact cells of wild type and cytochrome mutants ( cycA , cytC4 and pufC ) of Rubrivivax gelatinosus and Rhodobacter sphaeroides . Constant illumination from a laser diode or trains of saturating flashes enabled the kinetic separation of acceptor and donor redox processes, and the electron contribution from the cyt bc 1 complex via periplasmic cytochromes. Under continuous excitation, concentrations of oxidized cytochromes increased in three phases where light intensity, electron transfer rate and the number of reduced cytochromes were the rate liming steps, respectively. By choosing suitable flash timing, gradual steps of cytochrome oxidation in whole cells were observed; each successive flash resulted in a smaller, damped oxidation. We attribute this damping to lowered availability of reduced cytochromes resulting from both exchange (unbinding/binding) of the cytochromes and electron transfer at the reaction center interface since a similar effect is observed upon deletion of genes encoding periplasmic cytochromes. In addition, we present a simple model to calculate the damping effect; application of this method may contribute to understanding the function of the diverse range of c-type cytochromes in the electron transport chains of anaerobic phototrophic bacteria

Effect of azotobacter products on lettuce transplants

While the nutrient supply in conventional farming is mainly provided by fertilizers, the organic farmers have to use nutrient-rich organic materials to produce seedlings of high quality. The advantage of transplants use in the vegetable growing can be to realize earliness (it gives higher benefit), increase growth safety, etc. Effect of bacteria (like microbial agent) can transform faster the nutrients from organic material. It can give opportunity for organic manure to affect faster in the substrate. The aim of this research was to determine: growing lettuce seedling only with the use of organic materials, estimating the effectiveness of some microbial products in vegetable transplant growing, and effect of microbial products on efficiency of manures. The results show that the combination of organic fertilizers and soil bacteria has effect on the increasing of nitrogen up-take of plants

Prompt lead exposure of aqueous environment biomonitored by photosynthetic bacteria

Anthropogenic activities including industrialization, urbanization and growth of population have significantly increased concerns about detrimental effects of pollutants on health and environment. Among the heavy metal ions, lead (II) ions are especially toxic and hazardous. Here, we report the application of purple photosynthetic bacteria in biomonitoring of lead pollution in aqueous habitats. The monitoring method is based on light absorption and fluorescence responses of living microorganism to prompt appearance of lead ions in the solution. The Pb(II) ions penetrate the cell membrane immediately, attack and (in few mM external concentration) destroy the light harvesting system together with the reaction center protein. As these bacteria may act as bioaccumulators of lead, they can be also used for bioremediation of contaminated cultures. The advantages using photosynthetic bacteria for monitoring and accumulating Pb(II) pollution in aqueous environmental compartments are presented in the paper