Shuji Ohtani

A novel Δ9 acyl-lipid desaturase, DesC2, from cyanobacteria acts on fatty acids esterified to the sn−2 position of glycerolipids

Acyl-lipid desaturases are enzymes that convert a C-C single bond into a C=C double bond in fatty acids that are esterified to membrane-bound glycerolipids. Four types of acyl-lipid desaturase, namely DesA, DesB, DesC, and DesD, acting at the Delta12, Delta15, Delta9, and Delta6 positions of fatty acids respectively, have been characterized in cyanobacteria. These enzymes are specific for fatty acids bound to the sn-1 position of glycerolipids. In the present study, we have cloned two putative genes for a Delta9 desaturase, designated desC1 and desC2, from Nostoc species. The desC1 gene is highly similar to the desC gene that encodes a Delta9 desaturase that acts on C18 fatty acids at the sn-1 position. Homologues of desC2 are found in genomes of cyanobacterial species in which Delta9-desaturated fatty acids are esterified to the sn-2 position. Heterologous expression of the desC2 gene in Synechocystis sp. PCC 6803, in which a saturated fatty acid is found at the sn-2 position, revealed that DesC2 could desaturate this fatty acid at the sn-2 position. These results suggest that the desC2 gene is a novel gene for a Delta9 acyl-lipid desaturase that acts on fatty acids esterified to the sn-2 position of glycerolipids.

Desaturase genes in a psychrotolerant Nostoc sp. are constitutively expressed at low temperature.

Antarctic psychrotolerant, Nostoc sp. (SO-36), when grown at 25 degrees C and then shifted to 10 degrees C, showed an increase in the tri-unsaturated fatty acid [C(18:3(9,12,15))] at the expense of mono- [C(18:1(9))] and di-unsaturated [C(18:2(9,12))] fatty acids. These results indicate that the activities of the enzymes DesA and DesB are up-regulated, when cultures were grown at 10 degrees C or shifted to 10 degrees C from 25 degrees C. However, RT-PCR studies indicated a constitutive expression of desA, desB, desC, and desC2 genes when cultures grown at 25 degrees C were shifted to 10 degrees C. This constitutive expression of des genes is in contrast to that observed in mesophilic cyanobacteria, in which desA and desB are transcriptionally up-regulated in response to lowering of growth temperature.

Morphology and Taxonomy of Five Cephaleuros Species (Trentepohliaceae, Chlorophyta) from Japan, Including Three New Species

Suto Y. and Ohtani S. 2009. Morphology and taxonomy of five Cephaleuros species (Trentepohliaceae, Chlorophyta) from Japan, including three new species. Phycologia 48: 213–236. DOI: 10.2216/07-31.1 Five species of the genus Cephaleuros, including three new species, were collected on leaves, green twigs, and fruits of various woody plants from Japan. The three new species grow subcuticularly. Cephaleuros aucubae sp. nov. forms thalli in a thin layer or a raised spot showing open-filamentous growth, growing only on Aucuba japonica. Cephaleuros japonicus sp. nov. forms more or less a circular disk with pseudoparenchymatous growth in the central portion and open-filamentous growth in the marginal portion. It is one of the most common species in Japan, growing frequently on Camellia japonica, Cleyera japonica, Eurya japonica, and Symplocos lucida. Cephaleuros microcellularis sp. nov. forms a circular raised disk with pseudoparenchymatous growth, growing on Persea japonica and Symplocos lucida. Small filamentous and gametic cells and concentric zonal rings of gametangia and setae characterize the species. We present the first report of Cephaleuros biolophus in Japan. This species is characterized by subcuticular, subepidermal, and intramatrical growth, growing frequently on Castanopsis cupsidata var. sieboldii, Myrica rubra, and Quercus spp. The sporangiophores which project from the lower leaf surface, produce head cells and sporangiate-laterals terminally and laterally. Cephaleuros virescens, which so far has been the only known species in Japan, grows subcuticularly and forms a circular raised disk with pseoudoparenchymatous growth, inhabiting frequently Magnolia grandiflora and Persea thunbergii.

Plant Communities at Dronning Maud Land

Studies on vegetation in Dronning Maud Land have been performed for many years and most detailed results have been mainly published by Japanese Antarctic Research Expedition (JARE; e.g. Matsuda 1963,1968; Akiyama 1967; Nakanishi 1977; Kanda 1981,1986a,b; Newton et al. 1994). This chapter provides a new overview on vegetation research with aspects on their environmental constraints and focuses on moss, lichen and algal communities with different regional aspects in a wider area and their effects on vegetation development.

Morphological features and chromosome numbers in cultures of five Cephaleuros species (Trentepohliaceae, Chlorophyta) from Japan

The morphological features and chromosome numbers were examined in cultures of five species of Cephaleuros; C. aucubae, C. biolophus, C. japonicus, C. microcellularis, and C. virescens, collected from Japan. On agar media of Bolds basal medium and CA medium, radial growth of the algal colonies was vigorous in C. virescens, moderate in C. aucubae, and poor in C. microcellularis, but varied from poor to moderate in isolates of C. biolophus and C. japonicus. Filaments of C. virescens branched at an angle less than 40° and just below the cross walls, while those of the other species branched at an angle greater than 40° without relation to the cross walls. The length of filamentous cells was significantly smaller in C. microcellularis than in the other species. The chromosome number differed with the species: n = 22 in C. aucubae, n = 34 in C. biolophus, n = 18 in C. japonicus, n = 12 in C. microcellularis, and n = 24 in C. virescens. The chromosome number did not vary between isolates from filaments and gametes in C. aucubae and C. biolophus and among those from filaments, gametes, and zoospores in C. japonicus and C. virescens.

Seasonal development of five Cephaleuros species (Trentepohliaceae, Chlorophyta) on the leaves of woody plants and the behaviors of their gametes and zoospores

The infection cycle of five Cephaleuros species – C. aucubae, C. biolophus, C. japonicus, C. microcellularis, and C. virescens – was clarified by investigating seasonal development and gamete and zoospore behavior at study sites in Matsue, Shimane Prefecture, Japan. Fresh thalli or lesions appeared on the leaves of various woody plants from August and continued to develop in general from April to September in the following year. Gametangia and zoosporangia matured on 2‐ and 3‐year‐old leaves. Gametes were released in C. microcellularis samples collected from late March to late May and in samples of the other four species collected from late April to late July. Zoospores were released in C. biolophus, C. japonicus, and C. virescens samples collected from mid‐May to early August. In the present study, gametes did not conjugate but germinated like zoospores to produce new plants. After inoculation with zoospores and gametes that behave as asexual spores, fresh thalli or lesions became evident in 2–5 months following inoculation and gametes and zoospores were produced on the developed thalli or lesions the following year; one cycle of the infection was completed per year in the study area.

The Trentepohliales (Ulvophyceae, Chlorophyta): An Unusual Algal Order and its Novel Plant Pathogen—Cephaleuros

Most plant pathologists know certain algae can be used as gelling agents in culture media. Pathologists practicing in tropical or subtropical environments also know that some algae damage plants. The five genera in the order Trentepohliales (Chlorophyta) are unique and fascinating. Among other characteristics, they are subaerial, bright orange to red in color, and one genus, Cephaleuros, is a plant pathogen while another, Stomatochroon, is a space parasite. Cephaleuros causes algal spot and includes 17 accepted species. Of these, 13 develop between the cuticle and the epidermis of their hosts and four grow intercellularly. The latter are especially damaging, causing chlorosis and branch dieback. Zoospores and gametes germinate on plant surfaces during the rainy season and probably penetrate through breaks in the host cuticle. Their filamentous growth forms thalli that produce sporangiophores and spherical gametangia the following year. Several species of Cephaleuros have a broad host range and though their damage is usually superficial, it can be economically important on certain crops. Plant stress is the greatest predisposing factor to this algal disease. Management includes providing plants with sufficient moisture and nutrients, modifying cultural and harvesting practices, and planting resistant cultivars when available.

Holocene paleolimnological changes of Lake Oyako-ike in the Soya Kaigan of East Antarctica

Abstract We studied Holocene paleolimnological changes as a part of studies of global change in Lake Oyako-ike in the Soya Kaigan of Lützow-Holm Bay region in East Antarctica, inferred from organic components and microscopic observation of microalgae and cyanobacteria in a sediment core (Ok4C-01, core length 135 cm), along with sedimentary facies and accelerator mass spectrometry (AMS) 14C dating. The Ok4C-01 core was composed mainly of silt and fine sand containing laminae between 135 and 65.5 cm, overlain by cyanobacterial mud between 65.5 and 0 cm. The mean sedimentation rate and crustal uplift rate were estimated to be 0.69 mm/y and 2.2 mm/y, respectively. The crustal uplift rate of Lake Oyako-ike basin is similar to those of present uplift rates but is somewhat greater than those estimated in the Lambert Glacier region, East Antarctica. The low biological production with diatoms in coastal marine environments (135–74.75 cm, ca. 2170–1300 cal BP) changes into green sulfur bacteria in stratified saline lake environments (74.75–60.95 cm, ca.1300–1100 cal BP), and then high biological production with cyanobacteria and green algae in freshwater environments (60.95–0 cm, ca.1100–220 cal BP). The ongoing retreat of glaciers and ongoing isostatic uplift during the mid-Holocene Hypsithermal (4000–2000 years ago) and thereafter are the main reasons for this isolation, whereas eustatic sea level change is believed to have played only a minor role.

Detection of geosmin from Coelosphaerium kuetzingianum separated by a step density gradient medium from suspended materials in water in Lake Shinji, Japan

To identify the geosmin-producing organisms in Lake Shinji, Japan, we conducted preliminary chemical and biological investigations from April to July 2008, during which odor occurrence was observed. Geosmin was mainly detected in the suspended substance (SS) of lake water, and its concentration corresponded to the cell numbers of Coelosphaerium kuetzingianum (Cyanophyceae) and Monoraphidium contortum. C. kuetzingianum and Pseudodictyosphaeriumminusculum (Chlorophyceae; which occurred only in April) were separated from the lake water of 30 April to the lighter, interlayers in a step density gradient medium. The highest concentration of geosmin was detected in the portion of the lightest layer separated from the water sample by gas chromatography mass spectrometry (GC/MS). Observation under optical microscope confirmed that abundant C. kuetzingianum with some P. minusculum and a very rare unknown material was retained in this portion. Similarly C. kuetzingianum was separated by the step density gradient medium from the sediment of 7 May. Abundant C. kuetzingianum with rare bacteria was recognized in the portion of the lightest layer, which contained the highest concentration of geosmin. The cell numbers of C. kuetzingianum correlated with the concentration of geosmin in the separated portions of water samples. These results suggest that C. kuetzingianum probably produced geosmin, although there has been no report about this to now.