Shinichi Takaichi

Carotenoids in Algae: Distributions, Biosyntheses and Functions

For photosynthesis, phototrophic organisms necessarily synthesize not only chlorophylls but also carotenoids. Many kinds of carotenoids are found in algae and, recently, taxonomic studies of algae have been developed. In this review, the relationship between the distribution of carotenoids and the phylogeny of oxygenic phototrophs in sea and fresh water, including cyanobacteria, red algae, brown algae and green algae, is summarized. These phototrophs contain division- or class-specific carotenoids, such as fucoxanthin, peridinin and siphonaxanthin. The distribution of α-carotene and its derivatives, such as lutein, loroxanthin and siphonaxanthin, are limited to divisions of Rhodophyta (macrophytic type), Cryptophyta, Euglenophyta, Chlorarachniophyta and Chlorophyta. In addition, carotenogenesis pathways are discussed based on the chemical structures of carotenoids and known characteristics of carotenogenesis enzymes in other organisms; genes and enzymes for carotenogenesis in algae are not yet known. Most carotenoids bind to membrane-bound pigment-protein complexes, such as reaction center, light-harvesting and cytochrome b6f complexes. Water-soluble peridinin-chlorophyll a-protein (PCP) and orange carotenoid protein (OCP) are also established. Some functions of carotenoids in photosynthesis are also briefly summarized.

Roseiflexus castenholzii gen. nov., sp. nov., a thermophilic, filamentous, photosynthetic bacterium that lacks chlorosomes

A novel thermophilic, photosynthetic bacterium, designated strain HLO8T, was isolated from a bacterial mat in a Japanese hot spring. Morphologically, the isolate was an unbranched multicellular filament with a cell diameter of 0.8-1.0 microm. The bacterium was red to reddish-brown in colour and formed a distinct red bacterial mat in the natural environment. It was able to grow photoheterotrophically under anaerobic light conditions and also chemoheterotrophically under aerobic dark conditions. Optimal growth occurred at 50 degrees C and pH 7.5-8.0. The cells contained bacteriochlorophyll (Bchl) a and gamma-carotene derivatives as photosynthetic pigments, but lacked Bchl c and chlorosomes. Cellular fatty acids in the isolate were mainly C16:0, C14:0 and C15:0. The major quinone was menaquinone-11. The DNA G+C content was 62.0 mol% (by HPLC). Phylogenetic analysis based on 16S rDNA sequencing suggested that the isolate belonged to the anoxygenic filamentous phototrophic bacteria represented by Chloroflexus aurantiacus, but was clearly distant from all members in this group (the sequence similarities between the isolate and its relatives were less than 83.8%). Based on genotypic and phenotypic data, the name Roseiflexus castenholzii gen. nov., sp. nov. is proposed for this isolate; the type strain is HLO8T (= DSM 13941T = JCM 11240T).

Characterization of carotenoids in photosynthetic bacteria.

Publisher Summary This chapter describes the characterization of the carotenoids from E. longus by modern techniques; the procedures are applicable to other carotenoids from photosynthetic bacteria. In particular, the procedures for analysis of the absorption spectra may be useful. The characteristics of carotenoids in photosynthetic bacteria are (1) most carotenoids are an aliphatic type, except for some aromatic or fl end group types in the Chlorobiaceae and Chloroflexaceae; (2) the cross-conjugated aldehyde and the tertiary methoxy group are confined to the carotenoids of photosynthetic bacteria; (3) several kinds of carotenoids are found in each species; (4) all the carotenoids are bound to light-harvesting or reaction center complexes; and (5) structural elements, such as allenic or acetylenic bonds, epoxides or furanoxides, or C45 or C5o carotenoids are not encountered. Although photosynthetic bacteria synthesize pigments under anaerobic conditions, these aerobic bacteria cannot grow anaerobically even in the light and they synthesize pigments only under high aeration. This chapter describes the procedures for the identification of the carotenoid sulfates from this bacterium, including some specific methods.

Novel hydroxycarotenoids with improved antioxidative properties produced by gene combination in Escherichia coli.

We have used combinatorial biosynthesis to synthesize novel lipophilic carotenoids that are powerful cellular antioxidants. By co-expressing three different carotenoid desaturases in combination with a carotenoid hydratase, a cyclase, and a hydroxylase on compatible plasmids in Escherichia coli, we synthesized four novel carotenoids not previously detected in biological material or chemically synthesized. Their identification was based on their relative retention times on HPLC, spectroscopic properties, molecular weights, number of hydroxy groups, and 1H-NMR spectra. The carotenoids were designated as 1-HO-3′, 4′-didehydrolycopene, 3, 1′-(HO)2-γ-carotene, 1,1′-(HO)2-3, 4, 3′, 4′-tetradehydrolycopene, and 1, 1′-(HO)2-3, 4-didehydrolycopene. These novel acyclic derivatives differ from structurally related compounds by extension of the conjugated polyene chain as well as additional hydroxy groups at position C-1′. We determined their antioxidative activity in a liposome-membrane model system, which showed that their ability to protect against photooxidation and radical-mediated peroxidation reactions was linked to the length of the conjugated double-bond system and the presence of a single hydroxy group. The protection of membrane degradation was superior to the related 1-HO and 1, 1′-(HO)2 lycopene derivatives, making them interesting pharmaceutical candidates.

Quinones in chlorosomes of green sulfur bacteria and their role in the redox-dependent fluorescence studied in chlorosome-like bacteriochlorophyll c aggregates

Abstract The light-harvesting chlorosome antennae of anaerobic, photosynthetic green sulfur bacteria exhibit a highly redox-dependent fluorescence such that the fluorescence intensity decreases under oxidizing conditions. We found that chlorosomes from Chlorobium tepidum contain three isoprenoid quinone species (chlorobiumquinone, menaquinone-7, and an unidentified quinone that probably is a chlorobiumquinone derivative) at a total concentration of approximately 0.1 mol per mol bacteriochlorophyll c. Most of the cellular chlorobiumquinone was found in the chlorosomes and constituted about 70% of the total chlorosome quinone pool. When the quinones were added to artificial, chlorosome-like bacteriochlorophyll c aggregates in an aqueous solution, a high redox dependency of the fluorescence was observed. Chlorobiumquinones were most effective in this respect. A lesser redox dependency of the fluorescence was still observed in the absence of quinones, probably due to another unidentified redox-active component. These results suggest that quinones play a significant, but not exclusive role in controlling the fluorescence and in inhibiting energy transfer in chlorosomes under oxic conditions. Chlorosomes from Chloroflexus aurantiacus contained menaquinone in an amount similar to that of total quinone in Chlorobium tepdium chlorosomes, but did not contain chlorobiumquinones. This may explain the much lower redox-dependent fluorescence observed in Chloroflexus chlorosomes.

Carotenoids and carotenogenesis in cyanobacteria: unique ketocarotenoids and carotenoid glycosides

Abstract.Cyanobacteria grow by photosynthesis, and necessarily contain chlorophyll and carotenoids, whose main functions are light harvesting and photoprotection. In this review, we discuss the carotenoids, carotenogenesis pathways, and characteristics of carotenogenesis enzymes and genes in some cyanobacteria, whose carotenogenesis enzymes have been functionally confirmed. In these cyanobacteria, various carotenoids have been identified, including the unique ketocarotenoids, echinenone and 4-ketomyxol; and the carotenoid glycosides, myxol glycosides and oscillol diglycosides. From these findings, certain carotenogenesis pathways can be proposed. The different compositions of carotenoids among these species might be due to the presence or absence of certain gene(s), or to different enzyme characteristics. For instance, two distinct β-carotene ketolases, CrtO and CrtW, are properly used in two pathways depending on the species. One β-carotene hydroxylase, CrtR, has been identified, and its substrate specificities vary across species. At present, functionally confirmed genes have been found in only a few species, and further studies are needed.

Phylogeny and photosynthetic features of Thiobacillus acidophilus and related acidophilic bacteria : its transfer to the genus Acidiphilium as Acidiphilium acidophilum comb. nov

Phylogenetic analyses based on 16S rDNA sequences and genomic DNA-DNA relatedness showed that the sulphur-oxidizing facultative chemolithotroph Thiobacillus acidophilus was closely related to members of the genus Acidiphilium, which is a group of strictly aerobic, heterotrophic acidophiles now categorized into aerobic photosynthetic bacteria. Lipophilic pigment analyses revealed that zinc-chelated bacteriochlorophyll a and carotenoids occurred in appreciable amounts in T. acidophilus and all established species of the genus Acidiphilium. PCR experiments showed that T. acidophilus as well as Acidiphilium species contained puf genes, encoding the photosynthetic reaction centre proteins and the core light-harvesting complex of the purple bacteria. There were high similarities between T. acidophilus and Acidiphilium species in the primary structure of their reaction centre proteins deduced from the nucleotide sequence data. The phylogenetic tree of the reaction centre proteins was in agreement with the 16S rDNA sequence-based phylogenetic tree in the relationship between T. acidophilus and Acidiphilium species and between the Acidiphilium cluster and other purple photosynthetic bacteria. Based on these results, together with previous phylogenetic and phenotypic information, it is proposed to reclassify T. acidophilus (Guay and Silver) Harrison 1983 as Acidiphilium acidophilum comb. nov. The type strain is ATCC 27807T (= DSM 700T).

Genomic structure of an economically important cyanobacterium, Arthrospira (Spirulina) platensis NIES-39.

A filamentous non-N2-fixing cyanobacterium, Arthrospira (Spirulina) platensis, is an important organism for industrial applications and as a food supply. Almost the complete genome of A. platensis NIES-39 was determined in this study. The genome structure of A. platensis is estimated to be a single, circular chromosome of 6.8 Mb, based on optical mapping. Annotation of this 6.7 Mb sequence yielded 6630 protein-coding genes as well as two sets of rRNA genes and 40 tRNA genes. Of the protein-coding genes, 78% are similar to those of other organisms; the remaining 22% are currently unknown. A total 612 kb of the genome comprise group II introns, insertion sequences and some repetitive elements. Group I introns are located in a protein-coding region. Abundant restriction-modification systems were determined. Unique features in the gene composition were noted, particularly in a large number of genes for adenylate cyclase and haemolysin-like Ca2+-binding proteins and in chemotaxis proteins. Filament-specific genes were highlighted by comparative genomic analysis.

Roseateles depolymerans gen. nov., sp. nov., a new bacteriochlorophyll a-containing obligate aerobe belonging to the beta-subclass of the Proteobacteria.

Strains 61AT (T = type strain) and 61B2, the first bacteriochlorophyll (BChl) a-containing obligate aerobes to be classified in the beta-subclass of the Proteobacteria, were isolated from river water. The strains were originally isolated as degraders of poly(hexamethylene carbonate) (PHC). The organisms can utilize PHC and some other biodegradable plastics. The strains grow only under aerobic conditions. Good production of BChl a and caroterioid pigments is achieved on PHC agar plates and an equivalent production is observed under oligotrophic conditions on agar medium. Spectrometric results suggest that BChl a is present in light-harvesting complex I and the photochemical reaction centre. The main carotenoids are spirilloxanthin and its precursors. Analysis of the 16S rRNA gene sequence indicated that the phylogenetic positions of the two strains are similar to each other and that their closest relatives are the genera Rubrivivax, ideonella and Leptothrix with similarities of 96.3, 96.2 and 96.1%, respectively. The cells are motile, straight rods and contain poly-beta-hydroxybutyrate granules. Ubiquinone-8 is the predominant quinone. Vitamins are not required for growth. The G + C content of genomic DNA is 66.2-66.3 mol%. Genetic and phenotypic features suggest that the strains represent a new genus in the beta-subclass which is evenly distant from known genera. Consequently, the name Roseateles depolymerans gen. nov., sp. nov. is proposed for the strains; the type strain of Roseateles depolymerans is strain 61AT (= DSM 11813T).

The effect of growth conditions on the light-harvesting apparatus in Rhodopseudomonas acidophila.

The detailed effect on the light-harvesting apparatus of three different wild-type strains of Rhodopseudomonas acidophila in response to changes in both light-intensity and temperature have been investigated. In all three strains at high light-intensities (160 μmol s m2 and above) the only LH2 antenna complex synthesised is the B800–850 complex. In strains 7050 and 7750 as the light-intensity is lowered the B800–850 complex is gradually replaced by another type of LH2 the B800–820 complex. However, at no light-intensities studied is this changeover complete when the cells are grown at 30°C. If however, the light-intensity is lowered at temperatures below 25°C with strain 7750 there is a complete replacement of the B800–850 complex by the B800–820 complex. At all light-intensities and temperatures tested, strain 10050 only synthesised the B800–850 complex. Strain 7050 also responded to changes in light-intensity by altering its carotenoid composition. At high light-intensity the major carotenoids were rhodopin and rhodopin-glucoside, while at low light-intensities the major ones were rhodopinal and rhodopinal-glucoside. This change in carotenoid content started to occur at rather higher light-intensities than the switchover from B800–850 to B800–820.