Preliminary characterization of carbohydrate stores from chlorarachniophytes (Division: Chlorarachniophyta)

Chlorarachniophytes are amoeboid/flagellate eukaryotes that harbor reduced green algal endosymbionts. The carbohydrate stores of chlorarachniophyte algae have been investigated using methylation analysis to determine monosaccharide composition. An appreciable quantity of long chain β-1,3 glucan occurs in these algae. Immunogold electron microscopy using an antibody specific for (β-1,3 glucans localized (β-1,3 glucans within a vacuole in the host cell cytoplasm. The results suggest that photosynthate produced by the endosymbiont is stored by the host. Implications of the data for endosymbiosis are discussed.     

Lotharella vacuolata sp. nov., a new species of chlorarachniophyte algae, and time-lapse video observations on its unique post-cell division behavior

A new species of chlorarachniophyte alga, Lotharella vacuolata Ota et Ishida sp. nov., is described. This alga has been maintained as strain CCMP240 at the Provasoli‐Guillard National Center for Culture of Marine Phytoplankton at Bigelow Laboratory for Ocean Sciences. We examined in detail its morphology, ultrastructure and life cycle, using light microscopy, transmission electron microscopy and time‐lapse videomicroscopy. The dominant stage in the life cycle was represented by coccoid cells; however, amoeboid and flagellated stages were also observed. This alga showed unique post‐cell division behavior: one of the two daughter cells became amoeboid and escaped through a pore on the parental cell wall; the other daughter cell remained within the parental cell wall. Pyrenoid ultrastructure and nucleomorph location, which are used as the main generic criteria of chlorarachniophytes, confirmed that the strain CCMP240 is a member of Lotharella. This alga, however, was clearly distinguished from other known Lotharella species by the presence of large vacuoles, unusual post‐cell division behavior and some unique ultrastructural characters.     

TAXONOMIC STUDY OF BIGELOWIELLA LONGIFILA SP. NOV. (CHLORARACHNIOPHYTA) AND A TIME‐LAPSE VIDEO OBSERVATION OF THE UNIQUE MIGRATION OF AMOEBOID CELLS1

A new species of a chlorarachniophyte alga, Bigelowiella longifila sp. nov., is described. It is classified as a member of Bigelowiella as flagellate cells constitute the main stage of the life cycle. However, this alga is different from the only described species of the genus, B. natans Moestrup, in having a unique amoeboid stage in the life cycle. We observed an interesting behavior of amoeboid daughter cells after cell division: One of the two daughter cells inherits the long filopodium of the parental cell, and it subsequently transports its cell contents through the filopodium to develop at its opposite end. The other daughter cell forms a new filopodium. This unequal behavior of daughter cells may have evolved before the chlorarachniophytes and some colorless cercozoans diverged.     

Partenskyella glossopodia (Chlorarachniophyceae) possesses a nucleomorph genome of approximately 1 Mbp

The nucleomorph genome size of the recently described chlorarachniophyte Partenskyella glossopodia, which forms an independent lineage in the phylogeny of chlorarachniophytes, was analyzed by pulse‐field gel electrophoresis and Southern hybridization. These analyses showed that the nucleomorph genome of P. glossopodia is composed of three linear chromosomes that are about 445 kbp, 313 kbp, and 275 kbp in size. Thus, the total genome size is approximately 1033 kbp, which is significantly larger than the known size of chlorarachniophyte nucleomorph genomes, i.e. 330–610 kbp. This is the first study to report a nucleomorph genome that reaches approximately 1 Mbp in size.     

Actin and ubiquitin protein sequences support a cercozoan/foraminiferan ancestry for the plasmodiophorid plant pathogens

The plasmodiophorids are a group of eukaryotic intracellular parasites that cause disease in a variety of economically significant crops. Plasmodiophorids have traditionally been considered fungi but have more recently been suggested to be members of the Cercozoa, a morphologically diverse group of amoeboid, flagellate, and amoeboflagellate protists. The recognition that Cercozoa constitute a monophyletic lineage has come from phylogenetic analyses of small subunit ribosomal RNA genes. Protein sequence data have suggested that the closest relatives of Cercozoa are the Foraminifera. To further test a cercozoan origin for the plasmodiophorids, we isolated actin genes from Plasmodiophora brassicae, Sorosphaera veronicae, and Spongospora subterranea, and polyubiquitin gene fragments from P. brassicae and S. subterranea. We also isolated actin genes from the chlorarachniophyte Lotharella globosa. In protein phylogenies of actin, the plasmodiophorid sequences consistently branch with Cercozoa and Foraminifera, and weakly branch as the sister group to the foraminiferans. The plasmodiophorid polyubiquitin sequences contain a single amino acid residue insertion at the functionally important processing point between ubiquitin monomers, the same place in which an otherwise unique insertion exists in the cercozoan and foraminiferan proteins. Taken together, these results indicate that plasmodiophorids are indeed related to Cercozoa and Foraminifera, although the relationships amongst these groups remain unresolved.     

Lotharella reticulosa sp. nov.: a highly reticulated network forming chlorarachniophyte from the Mediterranean Sea

A new chlorarachniophyte Lotharella reticulosa sp. nov. is described from a culture isolated from the Mediterranean Sea. This strain is maintained as strain RCC375 at the Roscoff Culture Collection, France. This species presents a multiphasic life cycle: vegetative cells of this species were observed to be coccoid, but amoeboid cells with filopodia and globular suspended cells were also present in the life cycle, both of which were not dominant phases. Flagellate cells were also observed but remained very rare in culture. The vegetative cells were 9-16 μm in diameter and highly vacuolated, containing several green chloroplasts with a projecting pyrenoid, mitochondria, and a nucleus. The chloroplast was surrounded by four membranes possessing a nucleomorph in the periplastidial compartment near the pyrenoid base. According to ultrastructural observations of the pyrenoid and nucleomorph, the present species belongs to the genus Lotharella in the phylum Chlorarachniophyta. This taxonomic placement is consistent with the molecular phylogenetic trees of the 18S rRNA gene and ITS sequences. This species showed a unique colonization pattern. Clusters of cells extended cytoplasmic strands radially. Then, amoeboid cells being born proximately moved distally along the cytoplasmic strand like on a "railway track". Subsequently the amoeboid cell became coccoid near the strand. In this way, daughter cells were dispersed evenly on the substratum. We also observed that the present species regularly formed a structure of filopodial nodes in mid-stage and later-stage cultures, which is a novel phenotype in chlorarachniophytes. The unique colonization pattern and other unique features demonstrate that RCC375 is a new chlorarachniophyte belonging to genus Lotharella, which we describe as Lotharella reticulosa sp. nov.