Specific binding of DCCD to reaction centers of the photosynthetic bacterium Rhodospirillum rubrum and its effect of certain photosynthetic reactions

Rhodobacter sphaeroides as a model to study the ecotoxicity of 1-alkyl-3-methylimidazolium bromide

The purple non-sulfur bacterium Rhodobacter sphaeroides was selected as a biological model to investigate its response to the toxicity of 1-alkyl-3-methylimidazolium bromide ([C_nmim]Br), a type of ionic liquid (IL), with different alkyl chain lengths (n describes the number of carbon atoms in the alkyl chain). The inhibition of bacterial growth by [C_nmim]Br was positively correlated with n. Morphological characterization revealed that [C_nmim]Br caused cell membrane perforation. The signal amplitude of the electrochromic absorption band shift of endogenous carotenoids showed a negatively linear correlation with n, and the amplitude of the blue-shift of the B850 band in light-harvesting complex 2 showed a positively linear correlation with n. Furthermore, an increase in blocked ATP synthesis and increase in antioxidant enzyme activity were observed in chromatophores treated with ILs containing longer alkyl chains. In summary, the purple bacterium can be developed as a model to monitor ecotoxicity and examine the mechanism of IL toxicity.

Generation of a functional, semisynthetic [FeFe]-hydrogenase in a photosynthetic microorganism

[FeFe]-Hydrogenases are hydrogen producing metalloenzymes with excellent catalytic capacities, highly relevant in the context of a future hydrogen economy. Here we demonstrate the synthetic activation of a heterologously expressed [FeFe]-hydrogenase in living cells of Synechocystis PCC 6803, a photoautotrophic microbial chassis with high potential for biotechnological energy applications. H2-Evolution assays clearly show that the non-native, semi-synthetic enzyme links to the native metabolism in living cells.

Metabolic Changes in Synechocystis PCC6803 upon Nitrogen-Starvation: Excess NADPH Sustains Polyhydroxybutyrate Accumulation

Polyhydroxybutyrate (PHB) is a common carbon storage polymer among heterotrophic bacteria. It is also accumulated in some photoautotrophic cyanobacteria; however, the knowledge of how PHB accumulation is regulated in this group is limited. PHB synthesis in Synechocystis sp. PCC 6803 is initiated once macronutrients like phosphorus or nitrogen are limiting. We have previously reported a mutation in the gene sll0783 that impairs PHB accumulation in this cyanobacterium upon nitrogen starvation. In this study we present data which explain the observed phenotype. We investigated differences in intracellular localization of PHB synthase, metabolism, and the NADPH pool between wild type and mutant. Localization of PHB synthase was not impaired in the sll0783 mutant; however, metabolome analysis revealed a difference in sorbitol levels, indicating a more oxidizing intracellular environment than in the wild type. We confirmed this by directly measuring the NADPH/NADP ratio and by altering the intracellular redox state of wild type and sll0783 mutant. We were able to physiologically complement the mutant phenotype of diminished PHB synthase activity by making the intracellular environment more reducing. Our data illustrate that the NADPH pool is an important factor for regulation of PHB biosynthesis and metabolism, which is also of interest for potential biotechnological applications.

Inhibition and labelling of isolated reaction centers from Rhodobacter sphaeroides by dicyclohexylcarbodiimide

The effect of dicyclohexylcarbodiimide (DCCD) on electron transfer in the acceptor quinone complex of reaction centers (RC) from Rhodobacter sphaeroides is reported. DCCD covalently labelled the RC over a wide concentration range. At low concentrations (<10 μM) the binding was specific for the L subunit. At relatively high concentrations (>100 μM) DCCD accelerated the rate of charge recombination of the P(+)QB (-) state, consistent with a decrease in the equilibrium constant between QA (-)QB and QAQB (-). At similar concentrations, in the presence of cytochrome c as exogenous donor, turnover of the RC was inhibited such that only three cytochromes were oxidized in a train of flashes. Both these inhibitory effects were fully reversed by dialysis, indicating that stable covalent binding was not involved. Possible mechanisms of action are discussed in terms of the putative role of specific residues in proton transfer and protonation and release of quinol from the RC.

2-[8-14C]naphthyl 2-diazo-3,3,3-trifluoropropionate, a new carbene generating reagent for probing hydrophobic membrane domains

A new precursor of a lipophilic photolabel, 2-[8-14C]naphthyl 2-diazo-3,3,3-trifluoropropionate (NADIT) has been synthesized. The suitability of the reagent for labeling the hydrophobic core of membranes is demonstrated by studying its reactivity in chromatophores of Rhodospirillum rubrum G-9+. The label binds preferentially to the phospholipids and intrinsic membrane proteins. In isolated reaction centers treated with NADIT the hydrophobic subunits M and L are more labeled than the H subunit. The high reactivity, dark stability and ease of synthesis favors this very lipophilic reagent to identify the intrinsic hydrophobic sections of membrane proteins.