Controllable Synthesis of Porous and Hollow Nanostructured Catalyst Particles and Their Soot Oxidation.

The introduction of macroporous structures into three-way catalysts (TWCs) through polymer template-assisted spray drying has attracted attention because of its enhanced gas diffusion and catalytic performance. However, the surface charge effect of polymeric template components has not been investigated to control the structure of the TWC particles during synthesis. Thus, this study investigated the effect of template surface charges on the self-assembly behavior of TWC nanoparticles (NPs) during drying. The self-assembly of TWC NPs and polymer particles with different charges produced a hollow structure, whereas using the same charges generated a porous one. Consequently, the mechanism of particle self-assembly during drying and final structure particle formation is proposed in this study. Here, porous TWC particles demonstrated a faster oxidation of soot particles than that of hollow-structured particles. This occurred as a result of the larger contact area between the catalyst surface and the solid reactant. Our findings propose a fundamental self-assembly mechanism for the formation of different TWC structures, thereby enhancing soot oxidation performance using macroporous structures.

Complete biosynthetic pathway of the C50 carotenoid bacterioruberin from lycopene in the extremely halophilic archaeon Haloarcula japonica.

UNLABELLED: Haloarcula japonica, an extremely halophilic archaeon that requires high concentrations of NaCl for growth, accumulates the C50 carotenoid bacterioruberin (BR). By homology analysis, a gene cluster, including c0507, c0506, and c0505, was found and predicted to be involved in the synthesis of bacterioruberin. To elucidate the function of the encoded enzymes, we constructed Ha. japonica mutants of these genes and analyzed carotenoids produced by the mutants. Our research showed that c0507, c0506, and c0505 encoded a carotenoid 3,4-desaturase (CrtD), a bifunctional lycopene elongase and 1,2-hydratase (LyeJ), and a C50 carotenoid 2",3"-hydratase (CruF), respectively. The above three carotenoid biosynthetic enzymes catalyze the reactions that convert lycopene to bacterioruberin in Ha. japonica. This is the first identification of functional CrtD and CruF in archaea and elucidation of the complete biosynthetic pathway of bacterioruberin from lycopene. IMPORTANCE: Haloarcula japonica, an extremely halophilic archaeon, accumulates the C50 carotenoid bacterioruberin (BR). In this study, we have identified three BR biosynthetic enzymes and have elucidated their functions. Among them, two enzymes were found in an archaeon for the first time. Our results revealed the biosynthetic pathway responsible for production of BR in Ha. japonica and provide a basis for investigating carotenoid biosynthetic pathways in other extremely halophilic archaea. Elucidation of the carotenoid biosynthetic pathway in Ha. japonica may also prove useful for producing the C50 carotenoid BR efficiently by employing genetically modified haloarchaeal strains.

Two Distinct Enzymes Have Both Phytoene Desaturase and 3,4-Desaturase Activities Involved in Carotenoid Biosynthesis by the Extremely Halophilic Archaeon Haloarcula japonica.

The extremely halophilic archaeon Haloarcula japonica accumulates the C50 carotenoid, bacterioruberin (BR). To reveal the BR biosynthetic pathway, unidentified phytoene desaturase candidates were functionally characterized in the present study. Two genes encoding the potential phytoene desaturases, c0507 and d1086, were found from the Ha. japonica genome sequence by a homology search using the Basic Local Align Search Tool. Disruption mutants of c0507 and d1086 and their complemented strains transformed with expression plasmids for c0507 and d1086 were subsequently constructed. High-performance liquid chromatography (HPLC) ana-lyses of carotenoids produced by these strains revealed that C0507 and D1086 were both bifunctional enzymes with the same activities as both phytoene desaturase (CrtI) and 3,4-desaturase (CrtD). C0507 and D1086 complemented each other during BR biosynthesis in Ha. japonica. This is the first study to identify two distinct enzymes with both CrtI and CrtD activities in an extremely halophilic archaeon.

Identification of carotenoids from the extremely halophilic archaeon Haloarcula japonica.

The carotenoids produced by extremely halophilic archaeon Haloarcula japonica were extracted and identified by their chemical, chromatographic, and spectroscopic characteristics (UV-Vis and mass spectrometry). The composition (mol%) was 68.1% bacterioruberin, 22.5% monoanhydrobacterioruberin, 9.3% bisanhydrobacterioruberin, <0.1% isopentenyldehydrorhodopin, and trace amounts of lycopene and phytoene. The in vitro scavenging capacity of a carotenoid, bacterioruberin, extracted from Haloarcula japonica cells against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals was evaluated. The antioxidant capacity of bacterioruberin was much higher than that of ß -carotene.