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Highlights: [•] Carbon nanoparticlulate film electrodes were prepared by layer-by-layer method or by sol–gel process of hydrophobic precursor. [•] Hydrogenase adsorbed on carbon nanoparticulate electrodes allows for mediatorless bioelectrocatalytic hydrogen oxidation. [•] Co-immobilization of mediator does not significantly improve bioelectrocatalytic hydrogen oxidation with adsorbed hydrogenase. [Copyright &y& Elsevier]

The membrane protein FlhB is a highly conserved component of the flagellar secretion system. It is composed of an N-terminal transmembrane domain and a C-terminal cytoplasmic domain (FlhBC). Here, the crystal structures of FlhBC from Salmonella typhimurium and Aquifex aeolicus are described at 2.45 and 2.55 Å resolution, respectively. These flagellar FlhBC structures are similar to those of paralogues from the needle type III secretion system, with the major difference being in a linker that connects the transmembrane and cytoplasmic domains of FlhB. It was found that deletion of a short flexible loop in a globular part of Salmonella FlhBC leads to complete inhibition of secretion by the flagellar secretion system. Molecular-dynamics calculations demonstrate that the linker region is the most flexible part of FlhBC and that the deletion of the loop reduces this flexibility. These results are in good agreement with previous studies showing the importance of the linker in the function of FlhB and provide new insight into the relationship between the different parts of the FlhBC molecule. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogenase I from the hyperthermophilic bacterium Aquifex aeolicus is a good candidate for biotechnological devices thanks to its ability to oxidize hydrogen at high temperature, even in the presence of oxygen and CO. In order to enhance the enzyme stability and the catalytic efficiency, we investigated the hydrogen oxidation process with hydrogenase I embedded in a physiological-like environment. Hydrogenase I partners in the metabolic chain, namely membrane quinone and cytochrome b, were purified and fully characterized. The complex hydrogenase I–cytochrome b was inserted into liposomes. Surface Plasmon Resonance revealed that quinone took part in the stabilization of the complex. By use of molecular modelization and electrochemistry analysis, enzyme stability has been demonstrated to be stronger and enzymatic efficiency to be five times higher when hydrogenase is embedded into the liposomes. This result raises the possibility of using hydrogenases as biocatalysts in fuel cells. [ABSTRACT FROM AUTHOR]

3-Deoxy-d-manno-2-octulosonate-8-phosphate (KDO8P) synthase, catalyzes the aldol-type condensation between phosphoenolpyruvate (PEP) and d-arabinose-5-phosphate (A5P) to produce the unusual 8-carbon sugar KDO8P, and inorganic phosphate. A 15.5-kb segment containing the kdsA gene from the hyperthermophilic bacterium Aquifex pyrophilus was cloned from a genomic library and sequenced. The native kdsA gene lacks a typical ribosome binding site, but contains a conserved U,A-rich sequence upstream to the start codon. The purified kdsA gene product catalyzes the formation of KDO8P from its natural substrates, PEP and A5P, as determined by 1H NMR analysis. KDO8P synthase showed maximum activity at 80 °C and pH 5.5–6.0 at 10-min reaction assay. At temperatures of 70, 80, and 90 °C, the enzyme exhibited half-lives of 8.0, 2.25, and 0.5 h, respectively. The kinetic constants at 60 °C were KmA5P=70 μM, KmPEP=290 μM, and kcat=4 s-1. The isolated enzyme contained 0.19 and 0.26 mol iron and zinc, respectively, per mole of enzyme subunit. Treatment with metal chelators eliminated enzyme activity, and by the addition of several divalent metal ions, the activity was restored and even exceeded the original activity. These results indicate that A. pyrophilus KDO8P synthase is a metal-dependent enzyme. A C11A mutant of KDO8P synthase from A. pyrophulis retained less than 1% of the wild-type activity and was shown to be incapable of metal binding. [ABSTRACT FROM AUTHOR]

Green-coloured sediments in low-temperature geothermal surface features are typically indicative of photosynthetic activity. A near-boiling (89–93°C), alkali-chloride spring in the Taupō Volcanic Zone, New Zealand, was observed to have dark green sediments despite being too hot to support any known photosynthetic organisms. Analysis of aqueous and sediment microbial communities via 16S rRNA amplicon sequencing revealed them to be dominated by Aquifex spp. a genus of known hyperthermophilic hydrogen-oxidisers (69%–91% of operational taxonomic units (OTUs)), followed by groups within the Crenarchaeota (3%–20%), including the known iron-reducing genus Pyrobaculum. Cultivation experiments suggest that the green colouration of clay sediments in this spring may be due in part to ferruginous clays and associated compounds serving as substrates for the iron-reducing activity of low-abundance Pyrobaculum spp. These findings demonstrate the dynamic nature of microbe–mineral interactions in geothermal environments, and the potential ability of the rarer biosphere (1%–2% of observed sequences, cell densities of 450–33 000 g−1 sediment) to influence mineral formation at a macro-scale. [ABSTRACT FROM AUTHOR]