Akiko Yokoyama

Low molecular weight carbohydrates of the Bangiophycidae (Rhodophyta)

In the order Porphyridiales there are three clades based on molecular evidence. These show parallels with the low molecular weight carbohydrate (LMWCs) in different genera. Clade Porphyridiales 1 includes Dixoniella, Glaucosphaera, Rhodella, and one undescribed genus (3987) that all contain mannitol. Clade Porphyridiales 2 comprises taxa of the Stylonematales Rhodosorus and Stylonema species and contains digeneaside and sorbitol, whereas Chroodactylon has only sorbitol. In clade Porphyridiales 3 Flintiella, Porphyridium, and the undescribed genus (3797) all possess only floridoside. In the Erythropeltidales Rhodochaete contains floridoside and digeneaside, Erythrotrichia species contain only floridoside, Sahlingia subintegra has floridoside and traces of D‐floridoside, and Smithora has L‐isofloridoside plus floridoside. In the Compsopogonales Boldia and Compsopogon have only floridoside. Within these genera as presently circumscribed, the LMWCs appear to be a reliable character to supplement the usual cytological characters.

Ubiquity and quantitative significance of detoxification catabolism of chlorophyll associated with protistan herbivory

Chlorophylls are essential components of the photosynthetic apparati that sustain all of the life forms that ultimately depend on solar energy. However, a drawback of the extraordinary photosensitizing efficiency of certain chlorophyll species is their ability to generate harmful singlet oxygen. Recent studies have clarified the catabolic processes involved in the detoxification of chlorophylls in land plants, but little is understood about these strategies in aquatic ecosystem. Here, we report that a variety of heterotrophic protists accumulate the chlorophyll a catabolite 132,173-cyclopheophorbide a enol (cPPB-aE) after their ingestion of algae. This chlorophyll derivative is nonfluorescent in solution, and its inability to generate singlet oxygen in vitro qualifies it as a detoxified catabolite of chlorophyll a. Using a modified analytical method, we show that cPPB-aE is ubiquitous in aquatic environments, and it is often the major chlorophyll a derivative. Our findings suggest that cPPB-aE metabolism is one of the most important, widely distributed processes in aquatic ecosystems. Therefore, the herbivorous protists that convert chlorophyll a to cPPB-aE are suggested to play more significant roles in the modern oceanic carbon flux than was previously recognized, critically linking microscopic primary producers to the macroscopic food web and carbon sequestration in the ocean.

Corynoplastis japonica gen. et sp. nov. and Dixoniellales ord. nov. (Rhodellophyceae, Rhodophyta) based on morphological and molecular evidence

A new unicellular red alga, Corynoplastis japonica gen. et sp. nov., is described from Tobishima, Japan. Cells are spherical, 18–33 µm in diameter, pale purple to brownish red and surrounded by a mucilaginous sheath. A single chloroplast with many lobes extends from the cell periphery to the cell center. A peripheral thylakoid is present. A pyrenoid occurs at each innermost chloroplast lobe end and one or two thylakoids are present in the pyrenoid matrix. The nucleus is eccentric to peripheral and Golgi bodies are scattered throughout the cell and associated with endoplasmic reticulum. Cells have a slow random gliding motility. The low molecular weight carbohydrate mannitol is present in the cells. Molecular phylogenetic analysis indicates that this alga is closely related to members of the genus Rhodella. A new order, Dixoniellales, is established for Dixoniella, Neorhodella and Glaucosphaera based on molecular and ultrastructural evidence (Golgi bodies associated only with the nucleus). The redefined order Rhodellales in which Rhodella and Corynoplastis are placed is characterized ultrastructurally by Golgi bodies scattered throughout the cytoplasm and associated with endoplasmic reticulum.

132,173‐Cyclopheophorbide b enol as a catabolite of chlorophyll b in phycophagy by protists

Both 132,173‐cyclopheophorbide a and b enols were produced along with ingestion of green microalgae containing chlorophylls a and b by a centrohelid protist (phycophagy). The results suggest that chlorophyll b as well as chlorophyll a were directly degraded to colored yet non‐phototoxic catabolites in the protistan phycophagic process. Such a simple process by the predators makes a contrast to the much sophisticated chlorophyll degradation process of land plants and some algae, where phototoxicity of chlorophylls was cancelled through the multiple enzymatic steps resulting in colorless and non‐phototoxic catabolites.

Neorhodella cyanea, a new genus in the Rhodellophyceae (Rhodophyta)

J. Scott, A. Yokoyama, C. Billard, J. Fresnel, Y. Hara, K.A. West and J.A. West. 2008. Neorhodella cyanea, a new genus in the Rhodellophyceae (Rhodophyta). Phycologia 47: 560–572. DOI: 10.2216/08-27.1 The red algal unicell Rhodella cyanea (Rhodellophyceae) was reinvestigated. The cell ultrastructure is clearly dissimilar to that of the two other Rhodella species, R. maculata Evans and R. violacea (Kornmann) Wehrmeyer. Consequently, we have established Neorhodella gen. nov. Neorhodella cyanea possesses a large parietal chloroplast with numerous lobes extending into the cell center. The inner region of each lobe terminates near the central nucleus and contains several thylakoids sparsely covered by opposed, disc-shaped phycobilisomes. These regions are interpreted as multiple pyrenoids. Thylakoids are more numerous in other chloroplast regions where phycobilisomes are alternately spaced. A peripheral encircling thylakoid is absent and plastoglobuli, in unicellular red algae found only in the Rhodellophyceae, are found at the cell periphery. Golgi bodies are exclusively perinuclear, similar to Dixoniella and Glaucosphaera in the class Rhodellophyceae. Golgi cisternae appear closely opposed during some cell cycle stages, a feature found in no other unicells except members of the Rhodellophyceae. Several stages of mitosis were observed in Neorhodella. These suggest a pattern fairly typical of other unicellular red algae. Nucleus-associated organelles are polar rings, the division poles have conspicuous gaps in the mostly intact nuclear envelope and microtubules emanate from a flattened plate of membranes and moderately electron dense material, attaching to small kinetochores during mitosis and terminating near the former poles of telophase nuclei during migration of daughter nuclei. The low molecular weight carbohydrate of Neorhodella is mannitol, similar to Rhodella and Dixoniella.

Chloroplast rotation and morphological plasticity of the unicellular alga Rhodosorus (Rhodophyta, Stylonematales)

Time‐lapse videomicroscopy was used to film chloroplast rotation in the 13 isolates of Rhodosorus marinus Geitler and one isolate of Rhodosorus magnei Fresnel & Billard maintained in culture. Cell diameter, rates of chloroplast rotation and the number of chloroplast lobes were measured in all isolates. Chloroplast rotation is a definitive characteristic of the genus Rhodosorus and should be included in its taxonomic description. Isolates of the type species, R. marinus, measure 4–7 μm in diameter in low light (2–4 μmol photons m−2 s−1) and 4.5–11.5 μm in diameter in bright light (15–20 μmol photons m−2 s−1), and have two to seven chloroplast lobes. Rhodosorus magnei is 9 μm in diameter and has seven to nine chloroplast lobes in bright light. However, these cells are much smaller (approx. 4 μm diam.) and have only two to three chloroplast lobes when maintained in low light. The species R. magnei was created based on its larger cell size and numerous chloroplast lobes compared with R. marinus, but since these characteristics were found to be quite variable and dependant on culture conditions, they cannot be used to differentiate these two species.

The generic delimitation of Rhodella (Porphyridiales, Rhodophyta) with emphasis on ultrastructure and molecular phylogeny

We investigated the cellular features and molecular phylogeny of Rhodella species and related unicellular red algae including undescribed species that we isolated. Results provide a new taxonomic interpretation at both generic and specific levels. The genus Rhodella is defined by its pyrenoid that is free from any internal structures. Based on phylogenetic analysis using 18SrDNA, there are two possibilities for the generic delimitation of Rhodella: Rhodella sensu stricto and Rhodella sensu lato. The generic autonomy of Dixoniella and the taxonomic position of R. cyanea were also discussed.

New unicellular red alga, Bulboplastis apyrenoidosa gen. et sp. nov. (Rhodellophyceae, Rhodophyta) from the mangroves of Japan: Phylogenetic and ultrastructural observations

A novel unicellular red alga collected from a mangrove area on Iriomote Island in southwest Japan is described as Bulboplastis apyrenoidosa gen. et sp. nov. The cells are spherical, mean 11.2 µm in diameter, and surrounded by a thick mucilaginous sheath. The grayish‐green chloroplast has many lobes extending throughout the cell and lacks a pyrenoid. This chloroplast type is similar to Glaucosphaera vacuolata, but differs from other unicellular red algae. Plastoglobuli clusters occur beneath the chloroplast envelope but only at the cell periphery. A peripheral encircling thylakoid is absent. Golgi bodies surround the central nucleus, which is an arrangement shared with all members of the Dixoniellales. The subcellular features of some mitotic phases are quite similar to those of other unicellular red algae. A pair of ring‐shaped structures located within electron‐dense material can be seen in cells undergoing telophase. The size of the polar rings ranged within those reported from the Dixoniellales. A phylogenetic analysis based on small subunit rDNA indicates that B. apyrenoidosa is a member of the Dixoniellales and a sister lineage to Neorhodellaand Dixoniella.

Taxonomic study of a new eustigmatophycean alga, Vacuoliviride crystalliferum gen. et sp. nov.

This study investigated the taxonomic affiliation of the algal strain nak-9, which has been reported to absorb radioactive cesium with high efficiency, using light and electron microscopy, and molecular phylogenetic analysis based on 18S ribosomal RNA gene (rDNA) sequences. This alga is spherical and coccoid, with a smooth cell wall, large vacuole, crystalline structure, reddish globule, and refractile granules (lamellate vesicles). The cells possess one to several greenish parietal chloroplasts with a bulging pyrenoid surrounded by lamellate vesicles. The chloroplasts include orderly thylakoid lamellae but no girdle lamella. Molecular phylogenetic analysis suggests that strain nak-9 is a member of the eustigmatophycean clade, which includes Goniochloris, Pseudostaurastrum, and Trachydiscus. On the basis of these results, we propose that strain nak-9 (NIES-2860) comprises a new species and new genus of the Eustigmatophyceae, Vacuoliviride crystalliferum gen. et sp. nov.

Phylogeny, Ultrastructure, and Flagellar Apparatus of a New Marimonad Flagellate Abollifer globosa sp. nov. (Imbricatea, Cercozoa)

Abollifer is a little-known genus of marine heterotrophic flagellates with no ultrastructural and molecular information, and its taxonomic position remains uncertain. In this study, we report a new species of Abollifer, Abollifer globosa sp. nov., isolated from a seawater sample collected at Tokyo Bay. To reveal the taxonomic position and morphological characteristics of A. globosa, we performed light and electron microscopic observations and a phylogenetic analysis using small subunit ribosomal DNA sequences. A. globosa cells were 29.5 μm in length and 22.4 μm in width, oval or ovoid in shape with an apical projection. Two unequal flagella emerged from a deep subapical flagellar pit. The rim of the flagellar pit except for the ventral side was swollen. Electron microscopic observations showed that A. globosa possessed mitochondria with tubular cristae, a Golgi apparatus, microbodies, extrusomes, and many endosymbiotic bacteria. Basal bodies were arranged in parallel. The flagellar apparatus of A. globosa showed affinity with common gliding cercozoan flagellates. Our phylogenetic tree showed that A. globosa branched as the sister position of order Marimonadida (Imbricatea, Cercozoa). On the basis of the morphological and molecular phylogenetic analysis, we conclude that A. globosa is a new member of the order Marimonadida.