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Proton Pumping (proton + pumping)
Selected AbstractsActinorhodopsins: proteorhodopsin-like gene sequences found predominantly in non-marine environmentsENVIRONMENTAL MICROBIOLOGY, Issue 4 2008Adrian K. Sharma Summary Proteorhodopsins are light-energy-harvesting transmembrane proteins encoded by genes recently discovered in the surface waters of the world's oceans. Metagenomic data from the Global Ocean Sampling expedition (GOS) recovered 2674 proteorhodopsin-related sequences from 51 aquatic samples. Four of these samples were from non-marine environments, specifically, Lake Gatun within the Panama Canal, Delaware Bay and Chesapeake Bay and the Punta Cormorant Lagoon in Ecuador. Rhodopsins related to but phylogenetically distinct from most sequences designated proteorhodopsins were present at all four of these non-marine sites and comprised three different clades that were almost completely absent from marine samples. Phylogenomic analyses of genes adjacent to those encoding these novel rhodopsins suggest affiliation to the Actinobacteria, and hence we propose to name these divergent, non-marine rhodopsins ,actinorhodopsins'. Actinorhodopsins conserve the acidic amino acid residues critical for proton pumping and their genes lack genomic association with those encoding photo-sensory transducer proteins, thus supporting a putative ion pumping function. The ratio of recA and radA to rhodopsin genes in the different environment types sampled within the GOS indicates that rhodopsins of one type or another are abundant in microbial communities in freshwater, estuarine and lagoon ecosystems, supporting an important role for these photosystems in all aquatic environments influenced by sunlight. [source] The impact of metabolic state on Cd adsorption onto bacterial cellsGEOBIOLOGY, Issue 3 2007K. J. JOHNSON ABSTRACT This study examines the effect of bacterial metabolism on the adsorption of Cd onto Gram-positive and Gram-negative bacterial cells. Metabolically active Gram-positive cells adsorbed significantly less Cd than non-metabolizing cells. Gram-negative cells, however, showed no systematic difference in Cd adsorption between metabolizing and non-metabolizing cells. The effect of metabolism on Cd adsorption to Gram-positive cells was likely due to an influx of protons in and around the cell wall from the metabolic proton motive force, promoting competition between Cd and protons for adsorption sites on the cell wall. The relative lack of a metabolic effect on Cd adsorption onto Gram-negative compared to Gram-positive cells suggests that Cd binding in Gram-negative cells is focused in a region of the cell wall that is not reached, or is unaffected by this proton flux. Thermodynamic modeling was used to estimate that proton pumping causes the pH in the cell wall of metabolizing Gram-positive bacteria to decrease from the bulk solution value of 7.0 to approximately 5.7. [source] Decline in leaf growth under salt stress is due to an inhibition of H+ -pumping activity and increase in apoplastic pH of maize leavesJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 4 2009Britta Pitann Abstract In this study, salt-induced changes in the growth rate of maize (Zea mays L.) were investigated during the first phase of salt stress. Leaf growth was reduced in the presence of 100 mM NaCl, and effects were more pronounced for the salt-sensitive cv. Pioneer 3906 in comparison to the hybrid SR03. While hydrolytic activity of plasma membrane remained unaffected, H+ -pumping activity was reduced by 47% in Pioneer 3906, but was unchanged in SR03. Changes in apoplastic pH were detected by ratiometric fluorescence microscopy using the fluorescent dye fluorescein isothiocyanate-dextran (50 mM). Pioneer 3906 responded with an increase of 0.2 pH units in contrast to SR03 for which no apoplastic alkalization was found. With respect to the hypothesis that the apoplastic pH is influenced by salinity, it is suggested that salt resistance is partly achieved due to efficient H+ -ATPase proton pumping, which results in cell-wall acidification and loosening. [source] V-ATPase deactivation in blowfly salivary glands is mediated by protein phosphatase 2CARCHIVES OF INSECT BIOCHEMISTRY AND PHYSIOLOGY (ELECTRONIC), Issue 3 2009Martin Voss Abstract The activity of vacuolar H+ -ATPase (V-ATPase) in the apical membrane of blowfly (Calliphora vicina) salivary glands is regulated by the neurohormone serotonin (5-HT). 5-HT induces, via protein kinase A, the phosphorylation of V-ATPase subunit C and the assembly of V-ATPase holoenzymes. The protein phosphatase responsible for the dephosphorylation of subunit C and V-ATPase inactivation is not as yet known. We show here that inhibitors of protein phosphatases PP1 and PP2A (tautomycin, ocadaic acid) and PP2B (cyclosporin A, FK-506) do not prevent V-ATPase deactivation and dephosphorylation of subunit C. A decrease in the intracellular Mg2+ level caused by loading secretory cells with EDTA-AM leads to the activation of proton pumping in the absence of 5-HT, prolongs the 5-HT-induced response in proton pumping, and inhibits the dephosphorylation of subunit C. Thus, the deactivation of V-ATPase is most probably mediated by a protein phosphatase that is insensitive to okadaic acid and that requires Mg2+, namely, a member of the PP2C protein family. By molecular biological techniques, we demonstrate the expression of at least two PP2C protein family members in blowfly salivary glands. © 2009 Wiley Periodicals, Inc. [source] Engineering Propionibacterium acidipropionici for enhanced propionic acid tolerance and fermentationBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2009An Zhang Abstract Propionibacterium acidipropionici, a Gram-positive, anaerobic bacterium, has been the most used species for propionic acid production from sugars. In this study, the metabolically engineered mutant ACK-Tet, which has its acetate kinase gene knocked out from the chromosome, was immobilized and adapted in a fibrous bed bioreactor (FBB) to increase its acid tolerance and ability to produce propionic acid at a high final concentration in fed-batch fermentation. After about 3 months adaptation in the FBB, the propionic acid concentration in the fermentation broth reached ,100,g/L, which was much higher than the highest concentration of ,71,g/L previously attained with the wild-type in the FBB. To understand the mechanism and factors contributing to the enhanced acid tolerance, adapted mutant cells were harvested from the FBB and characterized for their morphology, growth inhibition by propionic acid, protein expression profiles as observed in SDS,PAGE, and H+ -ATPase activity, which is related to the proton pumping and cell's ability to control its intracellular pH gradient. The adapted mutant obtained from the FBB showed significantly reduced growth sensitivity to propionic acid inhibition, increased H+ -ATPase expression and activity, and significantly elongated rod morphology. Biotechnol. Bioeng. 2009; 104: 766,773 © 2009 Wiley Periodicals, Inc. [source] | |||||||||||||