Unequal divisions at the third cleavage increase the number of primary mesenchyme cells in sea urchin embryos

To clarify the distribution and behavior of the maternal factors that direct the differentiation of primary mesenchyme cells (PMC) in sea urchin embryos, unequal division was induced at the third cleavage with the treatment of dinitro-phenol (DNP), and the numbers of differentiated PMC were examined. The most surprising finding was that the number of PMC was considerably increased in some of the DNP-treated embryos. This increase in the number of PMC was suggested to be closely related to the size of the precocious micromeres formed at the 8-cell stage. By measuring both the size of the precocious micromeres and the number of PMC in individual embryos, it was suggested that almost all the descendants of the precocious micromeres differentiated into PMC, if the volume was less than 26 pL (about three times the volume of normal micromeres). Cell tracing experiments ascertained that precocious micromeres with small volumes behave just like micromeres formed at the fourth cleavage in normal embryos. The obtained results indicated that the maternal factors present in sea urchin embryos can direct, at least, more than three times the number of PMC, and that the number of cell divisions of the PMC lineage is not strictly regulated.     

Complete DNA sequence, specific Tn5 insertion map, and gene assignment of the carotenoid biosynthesis pathway of Rhodobacter sphaeroides.

The carotenoid biosynthesis genes form a cluster within the genome of Rhodobacter sphaeroides, lying in the middle of a larger cluster and 45 kb in length, which contains genes for bacteriochlorophyll biosynthesis and for the reaction center and light-harvesting apoproteins. The positions and approximate limits of the carotenoid genes were determined previously by localized transposon Tn5 mutagenesis and by comparison with the closely related Rhodobacter capsulatus carotenoid gene cluster. In this report, analysis of the DNA and deduced amino acid sequences of the carotenoid genes in R. sphaeroides are presented. Twenty-five Tn5 insertion mutants were used to produce a base-specific Tn5 insertion map of this region, and carotenoid gene assignment was supported by spectroscopic, ultrastructural, and high-pressure liquid chromatography analyses of these mutants. A region in the 3' end of crtD which affects bacteriochlorophyll biosynthesis was discovered, and CrtA was found to possess a proline-rich C-terminal region containing a repeated (Ala-Pro)n motif. CrtF also showed a high degree of sequence conservation with eukaryotic O-methyltransferases. This study provides gene sequences and assignments based upon a comprehensive structural, spectroscopic, and biochemical analysis of a range of carotenoid biosynthetic mutants; in each mutation, the point of Tn5 insertion is determined accurate to 1 bp on the gene cluster.     

Increases in Cellular Levels of Cytochrome cd1 in Roseobacter denitrificans upon Irradiation with Green Light during Aerobic Growth

The cellular level of cytochrome cd₁, the nitrite reductaseof the aerobic photosynthetic bacterium Roseobacter denitrificans,increased considerably when the cells were grown aerobicallyunder white light. The action spectrum for the increase, determinedboth spectroscopically and immunologically, revealed that greenlight at 561 nm was most effective, while blue light between400 and 500 nm was fairly effective. Red and far-red light (650–900nm) absorbed by the bacterio-chlorophyll had no effect, eventhough bacteriochlorophyll and carotenoids were formed normallyduring the growth of cells. Diphenylamine, an inhibitor of thebiosynthesis of carotenoids abolished the increase in levelsof the cytochrome, a result that suggests that a carotenoid(s)was responsible for this phenomenon. The bulk carotenoids seem,however, to be unlikely the candidates for the photoreceptorsbecause they did not accumulate in the light-grown cells. Attemptsto detect archaerhodopsin, 11-cis and all-trans retinal by immunologicalor HPLC analysis were unsuccessful. Although we failed to identifythe photoreceptor, it is clear that R. denitrificans has a green-lightsignal-transduction system that controls the expression of cytochromecd₁. (Received April 19, 1993; Accepted July 12, 1993)     

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 mol 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.     

Carotenoids from the aerobic photosynthetic bacterium,Erythrobacter longus: β-Carotene and its hydroxyl derivatives

About 20 different carotenoids were found in a strictly aerobic photosynthetic bacterium, Erythrobacter longus. All the carotenoids except the highly polar ones were identified as C₄₀-skeletal carotenoids, which could be devided into three groups: (1) bicyclic carotenoids: -carotene and its hydroxyl derivatives; -cryptoxanthin, zeaxanthin, caloxanthin and nostoxanthin, (2) monocyclic carotenoids: rubixanthin, bacteriorubixanthin and bacteriorubixanthinal, which was a unique cross-conjugated carotenal, and (3) acyclic carotenoids: anhydrorhodovibrin and spirilloxanthin. Bacteriorubixanthinal and zeaxanthin were the major components. (3R)-3-Hydroxy--ionone has rarely been found in carotenoids of purple photosynthetic bacteria, while the acyclic carotenoids have been found exclusively in photosynthetic bacteria. Thus, this bacterium is interesting in its composition of carotenoids.Abbreviations DPA diphenylamine - HPLC high-performance liquid chromatography - HP-TLC high-performance thin layer chromatography - FD-MS field desorption mass spectrometry - ¹HNMR proton nuclear magnetic resonance - CD circular dichroism     

Discovery of Natural Photosynthesis using Zn-Containing Bacteriochlorophyll in an Aerobic Bacterium Acidiphilium rubrum

We discovered natural photosynthesis using Zn-containing bacteriochlorophyll in an acidophilic bacterium Acidiphilium rubrum. Chemical analysisof the cell extracts gave a 13 : 2 :1 molar ratio of Zn-bacteriochlorophyll : Mg-bacteriochlorophyll : bacteriopheophytin . Most of thepigments are associated with fully active reaction center andlight-harvesting complexes analogous to those in purple photosyntheticbacteria. The finding indicates an unexpectedly wide variabilityof photosynthesis. ⁷Present address: Department of Ecological Engineering, ToyohashiUniversity of Technology, Tenpaku-cho, Toyohashi, 441 Japan     

Purification, characterization and crystallization of the core complex from thermophilic purple sulfur bacterium Thermochromatium tepidum

A light-harvesting-reaction center (LH1-RC) core complex has been highly purified from a thermophilic purple sulfur bacterium, Thermochromatium tepidum. The bacteriochlorophyll (BChl) a molecules in the LH1 exhibit a Q(y) transition at 914 nm, more than 25 nm red-shift from those of its mesophilic counterparts. The LH1-RC complex was isolated in a monomeric form as confirmed by sucrose density gradient centrifugation, blue native PAGE and size-exclusion chromatography. Four subunits (L, M, H and a tetraheme cytochrome) in RC and two polypeptides (alpha and beta) in LH1 were identified. Spirilloxanthin was determined to be the predominant carotenoid in the core complex. The purified core complex was highly stable, no significant change in the LH1 Q(y) transition was observed over 10 days of incubation at room temperature in dark. Circular dichroism spectrum of the LH1 complex was characterized by low intensity and nonconservative spectral shape, implying a high symmetry of the large LH1 ring and interaction between the BChl a and carotenoid molecules. A dimeric feature of the BChl a molecules in LH1 was revealed by magnetic circular dichroism spectrum. Crystals of the core complex were obtained which diffracted X-rays to about 10 A.     

Substrate specificities and availability of fucosyltransferase and beta-carotene hydroxylase for myxol 2'-fucoside synthesis in Anabaena sp. strain PCC 7120 compared with Synechocystis sp. strain PCC 6803

To elucidate the biosynthetic pathways of carotenoids, especially myxol 2'-glycosides, in cyanobacteria, Anabaena sp. strain PCC 7120 (also known as Nostoc sp. strain PCC 7120) and Synechocystis sp. strain PCC 6803 deletion mutants lacking selected proposed carotenoid biosynthesis enzymes and GDP-fucose synthase (WcaG), which is required for myxol 2'-fucoside production, were analyzed. The carotenoids in these mutants were identified using high-performance liquid chromatography, field desorption mass spectrometry, and (1)H nuclear magnetic resonance. The wcaG (all4826) deletion mutant of Anabaena sp. strain PCC 7120 produced myxol 2'-rhamnoside and 4-ketomyxol 2'-rhamnoside as polar carotenoids instead of the myxol 2'-fucoside and 4-ketomyxol 2'-fucoside produced by the wild type. Deletion of the corresponding gene in Synechocystis sp. strain PCC 6803 (sll1213; 79% amino acid sequence identity with the Anabaena sp. strain PCC 7120 gene product) produced free myxol instead of the myxol 2'-dimethyl-fucoside produced by the wild type. Free myxol might correspond to the unknown component observed previously in the same mutant (H. E. Mohamed, A. M. L. van de Meene, R. W. Roberson, and W. F. J. Vermaas, J. Bacteriol. 187:6883-6892, 2005). These results indicate that in Anabaena sp. strain PCC 7120, but not in Synechocystis sp. strain PCC 6803, rhamnose can be substituted for fucose in myxol glycoside. The beta-carotene hydroxylase orthologue (CrtR, Alr4009) of Anabaena sp. strain PCC 7120 catalyzed the transformation of deoxymyxol and deoxymyxol 2'-fucoside to myxol and myxol 2'-fucoside, respectively, but not the beta-carotene-to-zeaxanthin reaction, whereas CrtR from Synechocystis sp. strain PCC 6803 catalyzed both reactions. Thus, the substrate specificities or substrate availabilities of both fucosyltransferase and CrtR were different in these species. The biosynthetic pathways of carotenoids in Anabaena sp. strain PCC 7120 are discussed.