Glossomastix chrysoplasta n. gen., n. sp. (Pinguiophyceae), a new coccoidal, colony-forming golden alga from southern Australia

Glossomastix chrysoplasta gen. et sp. nov. is described from cultures isolated from sandstone rubble, Sorrento Back Beach, Mornington Peninsula, Victoria, Australia. The alga forms wall‐less, coccoidal vegetative cells that congregate in mucilaginous colonies and reproduce by successive bipartition. Plastids have girdle lamellae and partially embedded pyrenoids that are traversed by cytoplasmic channels. Zoospores are uniflagellate and swim poorly; a narrow lingulate pseudopod provides their primary form of motion. The single flagellum, which lacks hairs, a flagellar swelling, and autofluorescence, is the equivalent of the posterior flagellum in other golden algae. The anterior flagellum is absent; the basal body with which it would normally be associated is blind. The flagellar apparatus has two basal bodies, three microtubular roots, and a rhizoplast. The posterior (elder) basal body has a transitional helix that is proximal to the basal plate. Glossomastix chrysoplasta, placed in the Pinguiophyceae on the basis of molecular sequence and biochemical data, shares some ultrastructural features with other members of the class, especially Polypodochrysis teissieri, which has similar zoospores, but it also differs from other pinguiophytes in many respects. Glossomastix chrysoplasta is the pinguiophyte with, on average, the largest cells (exclusive of external materials), and it is the only one with a colonial habit.     

CHARACTERIZATION AND PHYLOGENETIC POSITION OF THE ENIGMATIC GOLDEN ALGA PHAEOTHAMNION CONFERVICOLA: ULTRASTRUCTURE, PIGMENT COMPOSITION AND PARTIAL SSU rDNA SEQUENCE

The morphology, ultrastructure, photosynthetic pigments, and nuclear-encoded small subunit ribosomal DNA (SSU rDNA) were examined for Phaeothamnion confervicola Lagerheim strain SAG119.79. The morphology of the vegetative filaments, as viewed under light microscopy, was indistinguishable from the isotype. Light microscopy, including epifluorescence microscopy, also revealed the presence of one to three chloroplasts in both vegetative cells and zoospores. Vegetative filaments occasionally transformed to a palmelloid stage in old cultures. An eyespot was not visible in zoospores when examined with light microscopy, but small droplets, similar to eyespot droplets, were apparent beneath the shorter flagellum when cells were viewed with electron microscopy. Zoospores had two flagella that were laterally inserted in the cell approximately one-third of the cell length from the apex. The longer flagellum was directed anteriorly and the shorter flagellum was directed posteriorly. Electron microscopy revealed the presence of tubular tripartite flagellar hairs on the longer flagellum, but no lateral filaments were found on the tripartite hairs. The general organization of the flagellar root system was similar to that of zoospores belonging to the Xanthophyceae and Phaeophyceae. However, the transitional region of the flagella contained a transitional helix with four to six gyres. Microtubular root R₁ consisted of six microtubules at its proximal end and one microtubule at its distal end. Roots R₂ and R₄ consisted of one microtubule each and root R₃ consisted of two microtubules. No rhizoplast was found. Thin-layer chromatography revealed the presence of fucoxanthin, diadinoxanthin, neoxanthin, and heteroxanthin as well as chlorophylls a, c₁ and c₂. High-performance liquid chromatography revealed the presence of fucoxanthin, diadinoxanthin, diatoxanthin, heteroxanthin, and β,β-carotene as well as chlorophylls a and c. The complete sequence of the SSU rDNA could not be obtained, but a partial sequence (1201 bases) was determined. Parsimony and neighbor-joining distance analyses of SSU rDNA from Phaeothamnion and 36 other chromophyte algae (with two Öomycete fungi as the outgroup) indicated that Phaeothamnion was a weakly supported (bootstrap = <50%, 52%) sister taxon to the Xanthophyceae representatives and that this combined clade was in turn a weakly supported (bootstrap = <50%, 67%) sister to the Phaeophyceae. Based upon ultrastructural observations, pigment analysis, and SSU rDNA phylogenetic analysis, Phaeothamnion is not a member of the Chrysophyceae and should be classified as incertae sedis with affinities to the Xanthophyceae and Phaeophyceae.     

ULTRASTRUCTURE AND 18S RRNA GENE SEQUENCE FOR PELAGOMONAS CALCEOLATA GEN. ET SP. NOV. AND THE DESCRIPTION OF A NEW ALGAL CLASS,THE PELAGOPHYCEAE CLASSIS NOV.1

Pelagomonas calceolata gen. et sp. nov., an ultra-planktonic marine alga, is described using electron microscopy and the cytoplasmic small subunit (18S) ribosomal RNA (rRNA) gene sequence. Cells are uniflagellate, about 1.5 × 3 μm in size. The flagellium has two rows of bipartite hairs, the paraxonemal rod has a dentate appearance, and a two-gyred transitional helix is present between two transitional plates. Microtubular roots, striated roots, and a second basal body are absent. A thin organic theca surrounds most of the cell. There is a single chloroplast with a girdle lamella and a single, dense mitochondrion with tubular cristae. A single Golgi body with swelled cisternae lies beneath the flagellum, and each cell has an ejectile organelle that putatwely releases a cylindrical structure. A vacuole, or cluster of vacuoles, contains the putative carbohydrate storage product. The 18S rRNA gene was sequenced completely in both directions, excluding three primer regions. When compared to the same gene sequence from other organisms, Pelagomonas calceolata gen. et sp. nov. occupies an unresolved position among other chromophyte algae and is distinct from members of any of these classes. Based on morphological, ultrastructural, and molecular data, we describe this alga as a new species, and we place this highly unusual new species in a new genus, family, order, and class.     

THE FLAGELLAR DEVELOPMENT CYCLE OF THE UNIFLAGELLATE PELAGOMONAS CALCEOLATA (PELAGOPHYCEAE)1

Vegetative cells of Pelagomonas calceolata Andersen & Saunders were confirmed to possess a reduced flagellar apparatus, consisting of a single basal body/flagellum that is not accompanied by either flagellar roots or a barren basal body. Just prior to division, the parental flagellum retracts (or is abscised) as two new basal bodies/flagella arise de novo. During cytokinesis the parental basal body segregates with a new basal body/flagellum, briefly producing a progeny cell typical of other known uniflagellates (i.e. containing a basal body/flagellum and accompanying barren basal body). The parental basal body then disintegrates or "transforms" out of existence, leaving both progeny cells with a single basal body/flagellum (i.e. neither progeny cell possesses any vestige of a mature flagellum/basal body ). Pelagomonas calceolata belongs to a lineage of chromophyte algae characterized by having a reduced flagellar apparatus, but it is the only known species, not only in this lineage but among all eukaryotes, to have undergone the complete elimination of the mature flagellum /basal body .     

79 Systematic revision of Phaeostrophion Irregulare (phaeophyceae) and proposal of a new family phaeostrophionaceae

Phaeostrophion irregulare S. & G. is distributed along the Pacific coast of NW America, and has been placed in the family Punctariaceae, order Dictyosiphonales (or Ectocarpales s.l.), based on morphological resemblances. Culture studies have indicated a direct life history, with erect thalli forming unilocular and/or plurilocular sporangia. However, the occurrence of a perennial prostrate system (holdfast), presence on the holdfast of marginal meristematic cells, and lack of pyrenoids in the chloroplasts, suggest that this taxonomic assignment is questionable. Our TEM observations confirm the lack of pyrenoids in the chloroplasts. The occurrence of reductive divisions in the unilocular sporangia was confirmed by comparing the DNA content in each nucleus using a fluorescent stain, but both unilocular and plurilocular sporangia-bearing erect thalli showed diploidy. Molecular phylogenetic analysis using rbcL (chloroplast) and 18S rDNA (nuclear) gene sequences reveals that Phaeostrophion is not included in the clade of Ecotocarpales s.l., but diverged relatively early in the evolution of Phaeophyceae, forming a clade with Sphacelariales and Syringodermatales, which share the apical/marginal meristematic mode of growth. Although we propose a new family Phaeostrophionaceae to accommodate Phaeostrophion , we suspend judgment of the appropriate taxonomic treatment at the ordinal level.     

Aurearenophyceae classis nova, a new class of Heterokontophyta based on a new marine unicellular alga Aurearena cruciata gen. et sp. nov. inhabiting sandy beaches

A new heterokontophyte alga, Aurearena cruciata gen. et sp. nov., was isolated from sandy beaches in Japan. Isolates were characterized by light and electron microscopy, spectroscopy of pigment composition, and molecular phylogenetic analyses using 18S rDNA and rbcL. The alga usually possessed a cell wall but also retained two heterokont flagella beneath the cell wall. Each walled cell first produced only a single flagellate cell that subsequently divided into two flagellate cells. Electron-opaque vesicles, possibly associated with cell wall formation, were observed beneath the cell membrane. The chloroplast consisted of two compartments, each enclosed by a chloroplast envelope and the inner membrane of the chloroplast endoplasmic reticulum; these two compartments were surrounded by a common outer membrane of chloroplast endoplasmic reticulum. Molecular phylogenetic trees suggested that this alga was a new and independent member of the clade that included the Phaeophyceae and Xanthophyceae (PX clade). A new class, Aurearenophyceae classis nova was proposed for A. cruciata.     

Symbiomonas scintillans gen. et sp. nov. and Picophagus flagellatus gen. et sp. nov. (Heterokonta): two new heterotrophic flagellates of picoplanktonic size

Two new oceanic free-living heterotrophic Heterokonta species with picoplanktonic size (< 2 microm) are described. Symbiomonas scintillans Guillou et Chrétiennot-Dinet gen. et sp. nov. was isolated from samples collected both in the equatorial Pacific Ocean and the Mediterranean Sea. This new species possesses ultrastructural features of the bicosoecids, such as the absence of a helix in the flagellar transitional region (found in Cafeteria roenbergensis and in a few bicosoecids), and a flagellar root system very similar to that of C. roenbergensis, Acronema sippewissettensis, and Bicosoeca maris. This new species is characterized by a single flagellum with mastigonemes, the presence of endosymbiotic bacteria located close to the nucleus, the absence of a lorica and a R3 root composed of a 6+3+x microtubular structure. Phylogenetical analyses of nuclear-encoded SSU rDNA gene sequences indicate that this species is close to the bicosoecids C. roenbergensis and Siluania monomastiga. Picophagus flagellatus Guillou et Chrétiennot-Dinet gen. et sp. nov. was collected in the equatorial Pacific Ocean. Cells are naked and possess two flagella. This species is characterized by the lack of a transitional helix and lateral filaments on the flagellar tubular hairs, the absence of siliceous scales, two unequal flagella, R1 + R3 roots, and the absence of a rhizoplast. SSU rDNA analyses place this strain at the base of the Chrysophyceae/Synurophyceae lineages.     

The structure and phylogenetic significance of the flagellar transition region in the chlorophyll c-containing algae.

An electron-dense helix is the most conspicuous structure in the flagellar transition region of members of the algal class Chrysophyceae. This “transitional helix” (TH) lies immediately distal to a partition across the flagellar axoneme which occurs exactly at the level at which the flagellum enters the cell body. The helix surrounds the central axonemal pair and lies at a distance of 10 nm from the 9 peripheral doublets. From the new data presented and a survey of published observations on the structure of the transition region of all the chlorophyll c-containing classes of algae, it is shown that a TH characteristic of the Chrysophyceae, Xanthophyceae and Eustigmatophyceae. The number of TH gyres varies from 3 to 6 in the Xanthophyceae and from 1 to 8 in the Chrysophyceae. In any one species, however, the TH is the same size in both the long flagellum which bears tubular mastigonemes and in the short smooth flagellum, though in some chrysophytes where the short flagellum is vestigial the number is fewer than in the normal flagellum. A TH appears to be absent from the Rhaphidophyceae and zoids of the Bacillariophyceae and Phaeophyceae though the structure of the transition region in these groups otherwise resembles that of the Chrysophyceae, Xanthophyceae and Eustigmatophyceae.The value of transition region variation in determining evolutionary relationships among the chlorophyll c-containing algal classes is assessed against a background of current ideas on their taxonomy and phylogeny. The relevant structural and biochemical features are tabled, and a phylogenetic scheme is presented which appears most logically to interpret these data. It is suggested that the line leading to the Eustigmatophyceae probably diverged from that leading to the strictly heterokont classes Xanthophyceae, Chrysophyceae, Phaeophyceae and Bacillariophyceae before evolution of a girdle lamella in the chloroplast and a photoreceptor apparatus involving a swelling at the proximal end of the short flagellum and an intraplastidial eyespot. The possession of a TH by both the Chrysophyceae and Xanthophyceae adds further support to the concept of their close relationship based on a range of other features. The exceptional absence of a TH from the chrysophycean genera Pedinella and Pseudopedinella reinforces the idea that these taxa are remote from the main chrysophycean line. Absence of a TH from the Phaeophyceae and Bacillariophyceae which otherwise share many important features with the Chrysophyceae and Xanthophyceae is probably a result of loss owing to the functional and morphological specialization of the zoids of these two groups. Transition region structure does not clarify the possible relationships of the Rhaphidophyceae, Prymnesiophyceae, Cryptophyceae or Dinophyceae.The proposed phylogeny supports the idea of a mutually related “heterokont” protist assemblage comprising the Chrysophyceae, Xanthophyceae, Phaeophyceae, Bacillariophyceae and possibly Rhaphidophyceae and the Oomycetes (water moulds) though in the latter the TH is replaced by a dense cylinder with a corrugated wall which may or may not be homologous with it. Structures resembling a TH have been described in a wide variety of other flagellated cells including the prasinophyte Pyraminonas orientalis, one species of the colourless flagellate genus Bicosoeca and the proteromonads Karotomorpha and Proteromonas. Only in the latter genera does homology with a TH seem likely on present evidence, suggesting that flagellates of this type may have evolved from chrysomonad-like ancestors.     

CELL WALL CHEMISTRY AND ULTRASTRUCTURE OF CHLOROCOCCUM OLEOFACIENS (CHLOROPHYCEAE)1,2

Cell walls of Chlorococcum oleofadens Trainor & Bold were examined ultrastructurally and chemically. The wall of zoospores has a uniform 30 nm width and a regular lamellar pattern. Zoospores and young vegetative cell walk exhibit periodicities, consisting of 20 nm ridges on the outer layer. Vegetative cell walls have a variable thickness of Up to 800 nm and are composed of multiple layers of electron dense material. Further, vegetative walk contain a microfibrillar material composed predominantly of glucose and presumed to be cellulose. Except for this cellulose, vegetative cell wall chemistry is very similar to that of Chlamydomemas being composed of glycoprotein rich in hydroxyproline. The hydroxyproline in Chlorococcum walls is linked glycosidically to a mixture of hetrooligosaccharides composed of arabinose and galactose, and in one instance, an unknown 6-deoxyhexose. Altogether, the glycoprotein complex accounts for at least 52% of the wall. The amino acid composition of the walls is stikingly similar to those of widely different plant species. Indirect evidence indicates zoospore cell walls are also chemically similar to those of Chlamydomonas, and like them, are cellulose free. Thus a major chemical difference between zoospore and vegetative cell walk of Chlorococcum is the presence of cellulose in the latter. The contribution of this microfibrillar cellulose to the physical properties of the vegetative wall is discussed.     

THE FLAGELLAR APPARATUS OF CHRYSOLEPIDOMONAS DENDROLEPIDOTA (CHRYSOPHYCEAE), A SINGLE-CELLED MONAD COVED WITH ORGANIC SCALES1

The flagellar apparatus of Chrysolepidomonas dedrolepidota Peters et Andersen is similar to that of other members of the Ochromonadales, Chrysophyceae. there are four microtubular roots (R_1-4) and a system II fiber (= rhizoplast). the R₁ root consists of three microtubules that nucleate many cytoplasmic microtubules. One compressed band of 10 or more cytoplasmic microtubules is directed black along the R1 root in an anti-parallel direction. The R₂ root consists of one to two microtubules, and it extends toward the distal end of the R₁ root. The R₃ root consists of six (?seven) microtubules near its proximal end. The “a” and “f” microtubules of the R₃ root are under the short flagellum, and the “f” microtubule loops back and under the basal body, extending down to the nucleus. The R₄ root consists of one to two microtubules extending along the left side of the shot flagellum and curving under the short flagellum where it terminates near the “a” microtubule of R₃ Both flagella have a transitional plate and a transitional helix with five gyres. There is a thin, second plate in the basal body at the level of the distal end of the “c” tubules of the basal body triplets. The tripartite flagellar hairs have long lateral filaments but lack short lateral filaments. We compare the flagellar apparatus with that of other members of the Ochromonadales and members of the Hydrurales and Hibberdiales.     

Phylogenetic relationships of the enigmatic angiosperm family Podostemaceae inferred from 18S rDNA and rbcL sequence data

The phylogenetic relationships of some angiosperm families have remained enigmatic despite broad phylogenetic analyses of rbcL sequences. One example is the aquatic family Podostemaceae, the relationships of which have long been controversial because of major morphological modifications associated with their aquatic habit. Podostemaceae have variously been associated with Piperaceae, Nepenthaceae, Polygonaceae, Caryophyllaceae, Scrophulariaceae, Rosaceae, Crassulaceae, and Saxifragaceae. Two recent analyses of rbcL sequences suggest a possible sister-group relationship of Podostemaceae to Crassulaceae (Saxifragales). However, the branch leading to Podostemaceae was long, and use of different outgroups resulted in alternative placements. We explored the phylogenetic relationships of Podostemaceae using 18S rDNA sequences and a combined rbcL + 18S rDNA matrix representing over 250 angiosperms. In analyses based on 18S rDNA data, Podostemaceae are not characterized by a long branch; the family consistently appears as part of a Malpighiales clade that also includes Malpighiaceae, Turneraceae, Passifloraceae, Salicaceae, Euphorbiaceae, Violaceae, Linaceae, Chrysobalanaceae, Trigoniaceae, Humiriaceae, and Ochnaceae. Phylogenetic analyses based on a combined 18S rDNA + rbcL data set (223 ingroup taxa) with basal angiosperms as the outgroup also suggest that Podostemaceae are part of a Malpighiales clade. These searches swapped to completion, and the shortest trees showed enhanced resolution and increased internal support compared to those based on 18S rDNA or rbcL alone. However, when Gnetales are used as the outgroup, Podostemaceae appear with members of the nitrogen fixing clade (e.g., Elaeagnaceae, Ulmaceae, Rhamnaceae, Cannabaceae, Moraceae, and Urticaceae). None of the relationships suggested here for Podostemaceae receives strong bootstrap support. Our analyses indicate that Podostemaceae are not closely allied with Crassulaceae or with other members of the Saxifragales clade; their closest relatives, although still uncertain, appear to lie elsewhere in the rosids.     

Supermatrix data highlight the phylogenetic relationships of photosynthetic stramenopiles

Molecular data had consistently recovered monophyletic classes for the heterokont algae, however, the relationships among the classes had remained only partially resolved. Furthermore, earlier studies did not include representatives from all taxonomic classes. We used a five-gene (nuclear encoded SSU rRNA; plastid encoded rbcL, psaA, psbA, psbC) analysis with a subset of 89 taxa representing all 16 heterokont classes to infer a phylogenetic tree. There were three major clades. The Aurearenophyceae, Chrysomerophyceae, Phaeophyceae, Phaeothamniophyceae, Raphidophyceae, Schizocladiophyceae and Xanthophyceae formed the SI clade. The Chrysophyceae, Eustigmatophyceae, Pinguiophyceae, Synchromophyceae and Synurophyceae formed the SII clade. The Bacillariophyceae, Bolidophyceae, Dictyochophyceae and Pelagophyceae formed the SIII clade. These three clades were also found in a ten-gene analysis. The approximately unbiased test rejected alternative hypotheses that forced each class into either of the other two clades. Morphological and biochemical data were not available for all 89 taxa, however, existing data were consistent with the molecular phylogenetic tree, especially for the SIII clade.     

ULTRASTRUCTURE OF SWARMERS IN THE LAMINARIALES (PHAEOPHYCEAE). I. ZOOSPORES1

Zoospores of 17 species in 14 genera of Laminariales, collected in the northeast Pacific Ocean, were studied by electron microscopy. These zoospores are unique in the brown algae in lacking both an eyespot in the single chloroplast and any associated swelling at the base of the shorter, posterior flagellum. Spores of all species examined possess a distal whiplash portion on the longer, mastigoneme-bearing anterior flagellum. This appendage may sometimes be as long as the mastigoneme-bearing portion of the flagellum, but it is only seldom preserved in the preparations for electron microscopy. A microtubular cytoskeleton is probably responsible for maintaining the shape of the spore. It consists of a short band of about 10 microtubules between the two basal bodies, scattered tubules converging at the anterior of the spore, a band of 7–9 tubules directed anteriorly from the anterior basal body, and a band directed posteriorly from the posterior basal body. These anterior and posterior bands may form one continuous band looping around the periphery of the spore. Variation with possible taxonomic significance was found in the ultrastructure of vesicles which apparently contain adhesive material, and which are extruded through the plasmalemma when the zoospores settle.     

Ultrastructure of spermatogenesis and spermatozoa of Cephalodasys maximus (Gastrotricha,Macrodasyida)

Summary Spermatogenesis and sperm ultrastructure of the macrodasyidan gastrotrich Cephalodasys maximus are described by means of transmission electron microscopy. The filiform sperm consists of an acrosomal accessory structure and an acrosomal vesicle, both being surrounded by spiralled material. The successive nuclear helix encloses the spiral-shaped mitochondrion and the axoneme of the flagellum is accompanied by dense strings, three helical elements and peripheral microtubules. During spermiogenesis the acrosomal accessory structure develops first and moves into a cell projection, where the spiral around this acrosomal rod forms. A nuclear section with condensed chromatin and one single fused large mitochondrion follow into the extension, becoming helical. A connecting clasp between nucleus and flagellum shortens to a cap-like structure. Parallel to the acrosomal and nuclear projection the flagellum develops where the spiralled elements and the basal plate form in succession, while the basal body shrinks.     

A sequence-specific DNA-binding factor (VF1) from Anabaena sp. strain PCC 7120 vegetative cells binds to three adjacent sites in the xisA upstream region.

A DNA-binding factor (VF1) partially purified from Anabaena sp. strain PCC 7120 vegetative cell extracts by heparin-Sepharose chromatography was found to have affinity for the xisA upstream region. The xisA gene is required for excision of an 11-kilobase element from the nifD gene during heterocyst differentiation. Previous studies of the xisA upstream sequences demonstrated that deletion of this region is required for the expression of xisA from heterologous promoters in vegetative cells. Mobility shift assays with a labeled 250-base-pair fragment containing the binding sites revealed three distinct DNA-protein complexes. Competition experiments showed that VF1 also bound to the upstream sequences of the rbcL and glnA genes, but the rbcL and glnA fragments showed only single complexes in mobility shift assays. The upstream region of the nifH gene formed a weak complex with VF1. DNase footprinting and deletion analysis of the xisA binding site mapped the binding to a 66-base-pair region containing three repeats of the consensus recognition sequence ACATT.     

A MOLECULAR PHYLOGENY OF THE HETEROKONT ALGAE BASED ON ANALYSES OF CHLOROPLAST-ENCODED rbcL SEQUENCE DATA1

Nearly complete ribulose-1,5-bisphosphate carboxylase/ oxygenase (rbcL)sequences from 27 taxa of heterokont algae were determined and combined with rbcL sequences obtained from GenBank for four other heterokont algae and three red algae. The phylogeny of the morphologically diverse haterokont algae was inferred from an unambiguously aligned data matrix using the red algae as the root, Significantly higher levels of mutational saturation in third codon positions were found when plotting the pair-wise substitutions with and without corrections for multiple substitutions at the same site for first and second codon positions only and for third positions only. In light of this observation, third codon positions were excluded from phylogenetic analyses. Both weighted-parsimony and maximum-likelihood analyses supported with high bootstrap values the monophyly of the nine currently recognized classes of heterokont algae. The Eustigmatophyceae were the most basal group, and the Dictyochophyceae branched off as the second most basal group. The branching pattern for the other classes was well supported in terms of bootstrap values in the weightedparsimony analysis but was weakly supported in the maximum-likelihood analysis (<50%). In the parsimony analysis, the diatoms formed a sister group to the branch containing the Chrysophyceae and Synurophyceae. This clade, charactetized by siliceous structures (frustules, cysts, scales), was the sister group to the Pelagophyceae/Sarcinochrysidales and Phaeo-/Xantho-/ Raphidophyceae clades. In the latter clade, the raphido-phytes were sister to the Phaeophyceae and Xanthophyceae. A relative rate test revealed that the rbcL gene in the Chrysophyceae and Synurophyceae has experienced a significantly different rate of substitutions compared to other classes of heterokont algae. The branch lengths in the maximum-likelihood reconstruction suggest that these two classes have evolved at an accelerated rate. Six major carotenoids were analyzed cladistically to study the usefulness of carotenoid pigmentation as a class-level character in the heterokont algae. In addition, each carotenoid was mapped onto both the rbcL tree and a consensus tree derived from nuclear-encoded small-subunit ribosomal DNA (SSU rDNA) sequences. Carotenoid pigmentation does not provide unambiguous phylogenetic information, whether analyzed cladistically by itself or when mapped onto phylogenetic trees based upon molecular sequence data.     

BOLIDOMONAS: A NEW GENUS WITH TWO SPECIES BELONGING TO A NEW ALGAL CLASS, THE BOLIDOPHYCEAE (HETEROKONTA)

A new algal class, the Bolidophyceae (Heterokonta), is described from one genus, Bolidomonas, gen. nov., and two species, Bolidomonas pacifica, sp. nov and Bolidomonas mediterranea, sp. nov., isolated from the equatorial Pacific Ocean and the Mediterranean Sea, respectively. Both species are approximately 1.2 μm in diameter and have two unequal flagella; the longer flagellum bears tubular hairs, whereas the shorter is smooth. The flagellar basal apparatus is restricted to two basal bodies, and there is no transitional helix. Cells are naked, devoid of walls or siliceous structures. The internal cellular organization is simple with a single plastid containing a ring genophore and a girdle lamella, one mitochondrion with tubular cristae, and one Golgi apparatus close to the basal bodies. The Mediterranean and the Pacific species differ in the insertion angle between their flagella and their pattern of swimming, these differences possibly being linked to each other. Analyses of the SSU rDNA gene place the two strains as a sister group to the diatoms. Moreover, pigment analyses confirm this position, as fucoxanthin is found as the major carotenoid in both lineages. These data strongly suggest that the ancestral heterokont that gave rise to the diatom lineage was probably a biflagellated unicell.     

Ultrastructure and 18S rDNA sequence analysis of Wobblia lunata gen. et sp. nov., a new heterotrophic flagellate (Stramenopiles, Incertae sedis)

A new heterotrophic flagellate Wobblia lunata gen. et sp. nov. is described. This organism usually attaches to the substratum showing a wobbling motion, and sometimes glides on the substratum or swims freely in the medium. W. lunata has various features characteristic of the stramenopiles. These include a hairy flagellum with tripartite tubular hairs, a mitochondrion with tubular cristae, arrangement of flagellar apparatus components and a double helix in the flagellar transition zone. W. lunata shares a double helix with heterotrophic stramenopiles, including Developayella elegans, oomycetes, hyphochytrids, opalinids and proteromonads, and could be placed in the phylum Bigyra Cavalier-Smith. However, from 18S rDNA tree analysis, these organisms form two distantly-related clades in the stramenopiles, and Wobblia appears at the base of the stramenopiles. Evaluation of morphological features and comparison of 18S rDNA sequences indicate that W. lunata is a member of the stramenopiles, but it is distinct from any other stramenopiles so far described. Its phylogenetic position within the stramenopiles is uncertain and therefore W. lunata is described as a stramenopile incertae sedis.     

Gene phylogenies and the endosymbiotic origin of plastids.

The endosymbiotic origin of chloroplasts from cyanobacteria has long been suspected and has been confirmed in recent years by many lines of evidence. Debate now is centered on whether plastids are derived from a single endosymbiotic event or from multiple events involving several photosynthetic prokaryotes and/or eukaryotes. Phylogenetic analysis was undertaken using the inferred amino acid sequences from the genes psbA, rbcL, rbcS, tufA and atpB and a published analysis (Douglas and Turner, 1991) of nucleotide sequences of small subunit (SSU) rRNA to examine the relationships among purple bacteria, cyanobacteria and the plastids of non-green algae (including rhodophytes, chromophytes, a cryptophyte and a glaucophyte), green algae, euglenoids and land plants. Relationships within and among groups are generally consistent among all the trees; for example, prochlorophytes cluster with cyanobacteria (and not with green plastids) in each of the trees and rhodophytes are ancestral to or the sister group of the chromophyte algae. One notable exception is that Euglenophytes are associated with the green plastid lineage in psbA, rbcL, rbcS and tufA trees and with the non-green plastid lineage in SSU rRNA trees. Analysis of psbA, tufA, atpB and SSU rRNA sequences suggests that only a single bacterial endosympbiotic event occurred leading to plastids in the various algal and plant lineages. In contrast, analysis of rbcL and rbcS sequences strongly suggests that plastids are polyphyletic in origin, with plastids being derived independently from both purple bacteria and cyanobacteria. A hypothesis consistent with these discordant trees is that a single bacterial endosymbiotic event occurred leading to all plastids, followed by the lateral transfer of the rbcLS operon from a purple bacterium to a rhodophyte.