bacteriochlorophylls and okenone

Okenone is a carotenoid pigment unique to certain members of Chromatiaceae, the dominant family of purple sulfur bacteria (PSB) found in euxinic photic zones. Diagenetic alteration of okenone produces okenane, the only recognized molecular fossil unique to PSB. The in vivo concentrations of okenone and bacteriochlorophyll a (Bchl a) on a per cell basis were monitored and quantified as a function of light intensity in continuous cultures of the purple sulfur bacterium Marichromatium purpuratum (Mpurp1591). We show that okenone-producing PSB have constant bacteriochlorophyll to carotenoid ratios in light-harvesting antenna complexes. The in vivo concentrations of Bchl a, 0.151 ± 0.012 fmol cell(-1), and okenone, 0.103 ± 0.012 fmol cell(-1), were not dependent on average light intensity (10-225 Lux) at both steady and non-steady states. This observation revealed that in autotrophic continuous cultures of Mpurp1591, there was a constant ratio for okenone to Bchl a of 1:1.5. Okenone was therefore constitutively produced in planktonic cultures of PSB, regardless of light intensity. This confirms the legitimacy of okenone as a signature for autotrophic planktonic PSB and by extrapolation water column euxinia. We measured the δ(13)C, δ(15)N, and δ(34)S bulk biomass values from cells collected daily and determined the isotopic fractionations of Mpurp1591. There was no statistical relationship in the bulk isotope measurements or stable isotope fractionations to light intensity or cell density under steady and non-steady-state conditions. The carbon isotope fractionation between okenone and Bchl a with respect to overall bulk biomass ((13)ε pigment - biomass) was 2.2 ± 0.4‰ and -4.1 ± 0.9‰, respectively. The carbon isotopic fractionation (13ε pigment-CO2) for the production of pigments in PSB is more variable than previously thought with our reported values for okenone at -15.5 ± 1.2‰ and -21.8 ± 1.7‰ for Bchl a.

Topics: Bacteriochlorophylls; Carbon Isotopes; Carotenoids; Chromatiaceae

Photophysical properties of two typical aryl carotenoids, okenone and chlorobactene, were studied with application of femtosecond and microsecond time-resolved absorption spectroscopies. These carotenoids are structurally similar and differ only by keto-group and character of the aryl ring. The studies have concentrated on aspects of the photochemistry of these carotenoids as possibility of solvent polarity induced formation of intramolecular charge transfer state in okenone, which contains a keto-group directly attached to the carbon-carbon double bond conjugation, estimating the energy of the forbidden first excited singlet electronic state, S1 (2(1)Ag(-)) and testing the photoprotective capabilities of okenone and chlorobactene in real biological systems. The energies of the S1 (2(1)Ag(-)) state obtained for these carotenoids are 12 750 cm(-1) for okenone and 13 450 cm(-1) for chlorobactene and are not affected either by temperature or solvent polarity. The effect of cryogenic temperature on the excited states lifetimes and energies was also studied at 77 K in 2-methyltetrahydrofuran, which forms a transparent glass upon freezing. The ability to quench bacteriochlorophylls triplets was studied on model bacteriochlorophyll a-carotenoid mixtures with application of flash photolysis. The triplet state lifetime obtained from the anticipated kinetic modelling of the rise and decay of the pool of carotenoid triplets are 2.1 μs for okenone and 2.8 μs for chlorobactene.

Topics: Absorption, Physicochemical; Bacteriochlorophylls; Carotenoids; Electron Transport; Energy Transfer; Solvents; Temperature

A rod-shaped, marine, phototrophic, purple sulfur bacterium containing gas vesicles was isolated from a marine solar saltern at Kakinada, India. Cells of strain JA134(T) are Gram-negative, non-motile rods, with vesicular intracytoplasmic membranes, and the strain has an absolute requirement for NaCl for growth. Bacteriochlorophyll a and the carotenoid okenone are present as photosynthetic pigments. Phylogenetic analysis on the basis of 16S rRNA gene sequences showed that strain JA134(T) clusters with members of the genus Halochromatium, but is distinctly separated from the species reported so far. The morphological and physiological differences of strain JA134(T) from other Halochromatium species support the description of strain JA134(T) (=ATCC BAA-1363(T) =DSM 18859(T) =JCM 14151(T)) as the type strain of a novel species, Halochromatium roseum sp. nov.

Topics: Bacterial Typing Techniques; Bacteriochlorophyll A; Carbohydrate Metabolism; Carotenoids; Chromatiaceae; Cytoplasmic Vesicles; DNA, Bacterial; DNA, Ribosomal; Genes, rRNA; India; Molecular Sequence Data; Photosynthesis; Phylogeny; RNA, Bacterial; RNA, Ribosomal, 16S; Seawater; Sequence Analysis, DNA; Sequence Homology, Nucleic Acid; Sodium Chloride