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 β -carotene.

Haloarcula japonica, an extremely halophilic archaeon that requires high concentrations of NaCl for growth, accumulates the C 50 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 C 50 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. IMPORTANCEHaloarcula japonica, an extremely halophilic archaeon, accumulates the C 50 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 C 50 carotenoid BR efficiently by employing genetically modified haloarchaeal strains.

Reactions of thiol with the C 3-vinyl group of various chlorophyll (Chl) derivatives were examined. The reactions resemble thiol-olefin co-oxidation, except that the vinyl C = C double bond was cleaved to afford a formyl group without any transition metal catalyst, and that the simple anti-Markovnikov adduct of thiol to olefin was obtained as a minor product. Peripheral substituents of Chl derivatives little affected the reaction, while the central metal atom of the chlorin macrocycle influenced the composition of the products. Oxygen and acid dissolved in the reaction mixture can facilitate the oxidation. Sufficiently mild conditions in this regioselective oxidation at the C 31-position are significant in bioorganic chemistry.

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