Dissolved inorganic carbon accumulating complexes from autotrophic bacteria from extreme environments

In nature, concentrations of dissolved inorganic carbon (DIC; = CO 2 + HCO 3 - + CO 3 2- ) can be low, and autotrophic organisms adapt with a variety of mechanisms to elevate intracellular DIC concentrations to enhance CO 2 fixation. Such mechanisms have been well-studied in Cyanobacteria , but much remains to be learned about their activity in other phyla. Novel multi-subunit membrane-spanning complexes capable of elevating intracellular DIC were recently described in three species of bacteria. Homologs of these complexes are distributed among 17 phyla in Bacteria and Archaea, and are predicted to consist of one, two, or three subunits. To determine whether DIC accumulation is a shared feature of these diverse complexes, seven of them, representative of organisms from four phyla, from a variety of habitats, and with three different subunit configurations were chosen for study. A high-CO 2 requiring, carbonic anhydrase-deficient ( yadF - cynT - ) strain of E. coli Lemo21(DE3), which could be rescued via elevated intracellular DIC concentrations, was created for heterologous expression and characterization of the complexes. Expression of all seven complexes rescued the ability of E. coli Lemo21(DE3) yadF - cynT - to grow under low CO 2 conditions, and six of the seven generated measurably elevated intracellular DIC concentrations when their expression was induced. For complexes consisting of two or three subunits, all subunits were necessary for DIC accumulation. Isotopic disequilibrium experiments clarified that CO 2 was the substrate for these complexes. In addition, the presence of an ionophore prevented the accumulation of intracellular DIC, suggesting that these complexes may couple proton potential to DIC accumulation. IMPORTANCE To facilitate the synthesis of biomass from CO 2 , autotrophic organisms use a variety of mechanisms to increase intracellular DIC concentrations. A novel type of multi-subunit complex has recently been described, which has been shown to generate measurably elevated intracellular DIC concentrations in three species of bacteria, begging the question of whether these complexes share this capability across the 17 phyla of Bacteria and Archaea where they are found. This study shows that DIC accumulation is a trait shared by complexes with varied subunit structures, from organisms with diverse physiologies and taxonomies, suggesting that this trait is universal among them. Successful expression in E. coli suggests the possibility of their expression in engineered organisms synthesizing compounds of industrial importance from CO 2 .

Reconciling Imbalanced Transition State Effects with Nonadiabatic CPET Reactions

Recently there have been several experimental demonstrations of how concerted proton electron transfer (CPET) reaction rates are affected by off-main-diagonal energies, namely the stepwise thermodynamic parameters ΔG°PT and ΔG°ET. Semi-classical structure-activity relationships have been invoked to rationalize these asynchronous linear free energy relation-ships despite the widely acknowledged importance of quantum effects such as nonadiabaticity and tunneling in CPET reactions. Here we report variable temperature kinetic isotope effect data for the asynchronous reactivity of a terminal Co-oxo complex with C–H bonds and find evidence of substantial quantum tunneling which is inconsistent with semi-classical models even when including tunneling corrections. This indicates substantial nonadiabatic tunneling in the CPET reactivity of this Co-oxo complex and further motivates the need for a quantum mechanical justification for the in-fluence of ΔG°PT and ΔG°ET on reactivity. To reconcile this dichotomy, we include ΔG°PT and ΔG°ET in nonadiabatic models of CPET by having them influence the anharmonicity and depth of the proton potential energy surfaces, which we approximate as Morse potentials. With this model we independently reproduce the dominant trend with ΔG°PT + ΔG°ET as well as the subtle effect of ΔG°PT − ΔG°ET (or η) in a nonadiabatic framework. The primary route through which these off-diagonal energies influence rates is through vibronic coupling. Our results reconcile predictions from semiclassical transition state theory with models that treat proton transfer quantum mechanically in CPET reactivity and suggest that similar treatments may be possible for other nonadiabatic processes.

Consumers’ attitudes towards purchase intention for local brand automobiles manufactured in Malaysia

The damaging effects of market globalization towards developing countries necessitate the exhibition of favorable attitudes towards purchase intention for local brand automobiles manufactured locally. With the application of moral foundation theory (MFT), a quantitative and cross-sectional study that involved 373 Proton potential consumers through a mall intercept survey in Malaysia was analyzed. The results show that Proton’s potential consumers had favorable attitudes towards purchase intention for Proton automobiles. Subsequent to a high mean score of collectivism and a moderate mean score of ethnocentrism, Proton potential consumers’ ethnocentric tendency offers a contradiction to extant literatures on consumer ethnocentrism in developing countries. Thus, our study posits that consumers from collectivistic societies are ethnocentric and further display favorable attitudes towards local products. Additionally, the predictive effects of consumer ethnocentrism and collectivism on attitudes towards purchase intention for local brand automobiles manufactured locally were ascertained. Our findings validated the applicability of MFT in explaining consumers’ attitudes towards local products. Other implications are also discussed.

Ultrafast dynamics of hydrated excess protons in CH3CN:H2O mixtures

In a combined experimental and theoretical 2D-IR and pump-probe study we determine how ultrafast solvent motions govern the vibrational dynamics of the hydrated proton and the key role played by the underlying proton potential.

Unraveling the structural and chemical features of biological short hydrogen bonds

Short hydrogen bonds are ubiquitous in biological macromolecules and exhibit distinctive proton potential energy surfaces and proton sharing properties.

Sulfur reduction coupled with anaerobic ammonium oxidation drove prebiotic proto-anabolic networks

SUMMARYThe geochemical energy that drove the transition from geochemistry to biochemistry on early Earth remains unknown. Here, we show that the reduction of sulfurous species, such as thiosulfate, sulfite, elemental sulfur, and sulfate, coupled with anaerobic ammonium oxidation (Sammox), could have provided the primordial redox equivalents and proton potential for prebiotic proto-anabolic networks consisting of the reductive acetyl-CoA pathway combined with the incomplete reductive tricarboxylic acid (rTCA) cycle under mild hydrothermal conditions. Sammox-driven prebiotic proto-anabolic networks (SPPN) include CO2 reduction, esterification, reductive amination, pyrrole synthesis, and peptides synthesis, in one geochemical setting. Iron-sulfur (FeS) minerals, as the proto-catalysts, enhanced the efficiency of SPPN. Thiols/thioesters were used as the energy currency in non-enzymatic phosphate-independent metabolism and accelerated SPPN. Peptides that consisted of 15 proteinogenic amino acids were the end products of SPPN with bicarbonate as the only source of carbon. Most peptides shared high similarity with the truly minimal protein content (TMPC) of the last universal common ancestor (LUCA). The peptides and/or proteinogenic amino acids might have endowed SPPN with autocatalysis and homochirality. Thus, Sammox drove the coupling transformation of carbon, hydrogen, oxygen, nitrogen, sulfur, and/or iron simultaneously in the far-from-equilibrium environment, thereby initiating the emergence of biochemistry. The existing Sammox microorganisms might belong to the phylum of Planctomycetes, and might be transitional forms between the three domains of life.

A Na+-coupled C4-dicarboxylate transporter (Asuc_0304) and aerobic growth of Actinobacillus succinogenes on C4-dicarboxylates

Actinobacillus succinogenes, which is known to produce large amounts of succinate during fermentation of hexoses, was able to grow on C4-dicarboxylates such as fumarate under aerobic and anaerobic conditions. Anaerobic growth on fumarate was stimulated by glycerol and the major product was succinate, indicating the involvement of fumarate respiration similar to succinate production from glucose. The aerobic growth on C4-dicarboxylates and the transport proteins involved were studied. Fumarate was oxidized to acetate. The genome of A. succinogenes encodes six proteins with similarity to secondary C4-dicarboxylate transporters, including transporters of the Dcu (C4-dicarboxylate uptake), DcuC (C4-dicarboxylate uptake C), DASS (divalent anion : sodium symporter) and TDT (tellurite resistance dicarboxylate transporter) family. From the cloned genes, Asuc_0304 of the DASS family protein was able to restore aerobic growth on C4-dicarboxylates in a C4-dicarboxylate-transport-negative Escherichia coli strain. The strain regained succinate or fumarate uptake, which was dependent on the electrochemical proton potential and the presence of Na+. The transport had an optimum pH ~7, indicating transport of the dianionic C4-dicarboxylates. Transport competition experiments suggested substrate specificity for fumarate and succinate. The transport characteristics for C4-dicarboxylate uptake by cells of aerobically grown A. succinogenes were similar to those of Asuc_0304 expressed in E. coli, suggesting that Asuc_0304 has an important role in aerobic fumarate uptake in A. succinogenes. Asuc_0304 has sequence similarity to bacterial Na+-dicarboxylate cotransporters and contains the carboxylate-binding signature. Asuc_0304 was named SdcA (sodium-coupled C4-dicarboxylate transporter from A . succinogenes).