Hisato Ikemoto

Fixation and utilization of carbon dioxide by microalgal photosynthesis

New microalgae were isolated as candidates for CO2 fixing biocatalyst. A new species of marine green alga, Chlorococcum littorale, exhibited the greatest CO2 fixation rate among the isolates, r g CO2 I−1 d−1 at pCO2 0.2. A unicellular red alga, Galdieria partita, showed the growth at pH 1, pCO2 1, 50 °C, and 50 ppm SO2 aeration. A newly identified Prasinophyte, Prasinococcus capsulatus, produced a large amount of extracellular polysaccharide that could be utilized as useful resources.

Distribution of betaine lipids in marine algae

Abstract DGCC(1,2-diacylglyceryl-3-( O -carboxyhydroxymethylcholine)) is a betaine lipid derived from Pavlova lutheri . The separation of this lipid from other polar lipids by HPLC was improved in order to survey the distribution of DGCC, other betaine lipids and PC (phosphatidylcholine) in marine algae. DGCC was found to be one of the common constituents of Haptophyceae; it was interesting to note that PC was not detected even as a minor component. DGTA(1,2-diacylglyceryl- O -2′-(hydroxymethyl)-( N , N , N -trimethyl)- β -alanine) was detected in five out of 16 species of Haptophyceae, whereas DGTS(1,2-diacylglyceryl- O -4′-( N , N , N -trimethyl)homoserine) was not detected. DGCC was also detected in four strains of Dinophyceae and a strain of Bacillariophyceae. Acyl moieties of DGCC in Haptophyceae were 16:0, 18:0 or 18:1 and C 20 or C 22 polyunsaturated fatty acids.

ACARYOCHLORIS MARINA GEN. ET SP. NOV. (CYANOBACTERIA), AN OXYGENIC PHOTOSYNTHETIC PROKARYOTE CONTAINING CHL D AS A MAJOR PIGMENT1

The phylogenetic position of an oxygenic photosynthetic prokaryote containing chl d as a major pigment, which have been tentatively named “Acaryochloris marina,” was analyzed using small subunit rDNA sequences. Phylogenetic relationships inferred among A. marina, selected strains from the Cyanobacteria, and plastids showed that A. marina was within the cyanobacterial radiation. The A. marina lineage diverged independently from other phylogenetic subgroups of the Cyanobacteria. No organism was found to be identical or related closely to A. marina by a similarity search and phylogenetic analysis. Based on these results, in addition to the reported characteristics of the cell morphology, pigment composition, and photosynthesis, a new taxon, Acaryochloris marina Miyashita et Chihara gen. et sp. nov., is formally proposed for the oxy‐genic photosynthetic prokaryote.

Pinguiochrysis pyriformis gen. et sp. nov. (Pinguiophyceae), a new picoplanktonic alga isolated from the Pacific Ocean

Pinguiochrysis pyriformis gen. et sp. nov. is a brown, naked, non‐motile, marine picoplankton. A culture was established from a surface sample collected in 1991 from the tropical Western Pacific Ocean. Typical cells of P. pyriformis are distinctively pear‐shaped and have one ovoid chloroplast; these two features distinguish this species from the other picophytoplankton species. However, the pyriform morphology is not consistent and cells frequently change to a subspherical shape. The chloroplast and mitochondrion ultrastructure confirm that this species belongs to the photosynthetic stramenopiles (chromophytes). Additional distinctive ultrastructural characteristics of P. pyriformis include (i) a chloroplast envelope forming a tubular invagination that penetrates into the pyrenoid; (ii) thylakoid lamellae consisting of more than three layers in some cells; (iii) the lack of basal bodies and centrioles; and (iv) the lack of scales or other extracellular structures. Based on the morphological features, this picoplanktonic species was described as a new species and placed in the Pinguiophyceae on the basis of the molecular phylogenetic analysis and biochemical data published elsewhere.

Fatty acid composition of a new marine picoplankton species of the Chromophyta

A marine yellowish picoplankton, strain PP301, which was newly isolated from the surface seawater of the western Pacific Ocean was an eminent producer of polyunsaturated fatty acids. Its fatty acids were mostly shared by the shortest saturated form (14:0, 20–30%) and polyunsaturated forms (20:4, EPA and DHA) which accounted for about 50% of the total fatty acids. The amount of intermediate forms in 16 and 18 carbon chains were very little. This composition was consistently observed irrespective of the growth temperatures (15–35 °C).