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.     

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.     

Molecular, morphological and phylogenetic characterization of six chlorarachniophyte strains

We compare and contrast the morphological and molecular features of six chlorarachniophyte strains, and examine their evolutionary origins. Electron microscopical studies of nucleomorphs and chloroplasts, characterization of nucleomorph karyotypes, and phylogenetic analyses of small subunit ribosomal RNA (srRNA) genes derived from the nucleomorph and host cell genomes have been used to separate the six strains into three distinct groups. One group, dubbed the‘beast group’, contains the strains Chlorarachnion sp. 242, Chlor-arachnion sp. 621, Chlorarachnion sp. 1408 and Chlorarachnion sp. 1481. Members of the beast group have a novel flagellate form and are apparently picoplank-tonic. The other two groups currently contain only one species each: Chlorarachnion reptans and Lotharella sp. 240. All chlorarachniophyte nucleomorphs examined house three small linear chromosomes each furnished with telomeres and srRNA genes.     

Phylogeny and nucleomorph karyotype diversity of chlorarachniophyte algae

Chlorarachniophytes are flagellated and/or reticulopod-forming marine algae with chlorophyll a- and b-containing plastids of secondary endosymbiotic origin. They are one of only two algal groups known to possess a "nucleomorph" (i.e. the remnant nucleus of the eukaryotic endosymbiont that donated the plastid). Apart from the recently sequenced nucleomorph genome of Bigelowiella natans, little is known about the size, structure, and composition of chlorarachniophyte nucleomorph genomes. Toward the goal of better understanding nucleomorph genome diversity, as well as establishing a phylogenetic framework with which to interpret variation in chlorarachniophyte morphology, ultrastructure, and life cycle, we are studying a wide range of chlorarachniophyte strains from public culture collections and natural habitats. We have obtained 22 new chlorarachniophyte nuclear and nucleomorph 18S rRNA gene (18S rDNA) sequences and nucleomorph genome size estimates for 14 different strains. Consistent with previous studies, all of the chlorarachniophytes examined appear to possess three nucleomorph chromosomes. However, our results suggest considerable variation in nucleomorph genome size and structure, with individual chromosome sizes ranging from approximately 90 to approximately 210 kbp, and total genome sizes between approximately 330 kbp in Lotharella amoebiformis and approximately 610 kbp in unidentified chlorarachniophyte strain CCMP622. The significance of these phylogenetic and nucleomorph karyotype data is discussed.     

Nucleomorph and plastid genome sequences of the chlorarachniophyte Lotharella oceanica: convergent reductive evolution and frequent recombination in nucleomorph-bearing algae

Background

Nucleomorphs are residual nuclei derived from eukaryotic endosymbionts in chlorarachniophyte and cryptophyte algae. The endosymbionts that gave rise to nucleomorphs and plastids in these two algal groups were green and red algae, respectively. Despite their independent origin, the chlorarachniophyte and cryptophyte nucleomorph genomes share similar genomic features such as extreme size reduction and a three-chromosome architecture. This suggests that similar reductive evolutionary forces have acted to shape the nucleomorph genomes in the two groups. Thus far, however, only a single chlorarachniophyte nucleomorph and plastid genome has been sequenced, making broad evolutionary inferences within the chlorarachniophytes and between chlorarachniophytes and cryptophytes difficult. We have sequenced the nucleomorph and plastid genomes of the chlorarachniophyte Lotharella oceanica in order to gain insight into nucleomorph and plastid genome diversity and evolution.

Results

The L. oceanica nucleomorph genome was found to consist of three linear chromosomes totaling ~610 kilobase pairs (kbp), much larger than the 373 kbp nucleomorph genome of the model chlorarachniophyte Bigelowiella natans. The L. oceanica plastid genome is 71 kbp in size, similar to that of B. natans. Unexpectedly long (~35 kbp) sub-telomeric repeat regions were identified in the L. oceanica nucleomorph genome; internal multi-copy regions were also detected. Gene content analyses revealed that nucleomorph house-keeping genes and spliceosomal intron positions are well conserved between the L. oceanica and B. natans nucleomorph genomes. More broadly, gene retention patterns were found to be similar between nucleomorph genomes in chlorarachniophytes and cryptophytes. Chlorarachniophyte plastid genomes showed near identical protein coding gene complements as well as a high level of synteny.

Conclusions

We have provided insight into the process of nucleomorph genome evolution by elucidating the fine-scale dynamics of sub-telomeric repeat regions. Homologous recombination at the chromosome ends appears to be frequent, serving to expand and contract nucleomorph genome size. The main factor influencing nucleomorph genome size variation between different chlorarachniophyte species appears to be expansion-contraction of these telomere-associated repeats rather than changes in the number of unique protein coding genes. The dynamic nature of chlorarachniophyte nucleomorph genomes lies in stark contrast to their plastid genomes, which appear to be highly stable in terms of gene content and synteny.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-374) contains supplementary material, which is available to authorized users.     

Morphological, physiochemical and molecular characterization of Anabaena strains

A set of 30 Anabaena strains, isolated from diverse geographical regions of India, were characterized using morphological and physiochemical attributes as well as molecular marker profiles. Significant differences were observed among the Anabaena strains with regard to the shape and size of trichomes and individual cells within a filament, besides qualitative and quantitative aspects of phycobiliprotein accumulation and activities of enzymes involved in nitrogen metabolism. Analyses of molecular polymorphisms in a selected set of 13 Anabaena strains, using primers based on repetitive sequences in the genome, led to unambiguous differentiation of the strains as well as understanding of their genetic relationships. Informative morphological, physio-chemical and molecular characters have been identified that could aid in differentiation and utilization of Anabaena strains as bioinoculants or as sources of pigments.     

Westerdykella globosa,a proposal for a new combination

The surface ornamentation of ascospores ofPreussia globosa was compared in an isolate from paddy soil in Japan and a culture derived from the holotype. The ascospores of two cultures were characterized by the surface ornamentation of a single, semicircular spiral ridge. This new finding strongly suggested that the fungus should be transferred to the genusWesterdykella. Therefore, the morphological and cultural characters of the fungus were re-examined, and the new combinationWesterdykella globosa is herein proposed.     

Intraregional variation among Alexandrium catenella (Dinophyceae) strains from southern Chile: Morphological,toxicological and genetic diversity

Morphological, toxicological and phylogenetic analyses, using the partial LSU gene and internal spacer (ITS) regions of the rDNA gene, were combined to evaluate the intraregional diversity of Alexandrium catenella occurring along the southern coast of Chile. Twenty-two strains isolated from different localities along the wide area of distribution of the species (from 42°S to 55°S) were examined by these three approaches. Morphologically, although the strains showed diagnostic characters according to the species definition, variations in these traits within and between strains were also observed. The absence of an apical or posterior attachment pore, for instance, was observed mainly in old isolates. Indirect connection between the apical and 1′ plates, traits normally seen in other species of the same genus, was also noted in some strains. However, the lack of a ventral pore on the 1′ plate was one of the most distinctive characteristics present in all the Chilean strains. Toxicologically, the Chilean strains were characterized by the dominance of N-sulfocarbamate (C1,2) and gonyautoxins (GTX1–4), but also by the scarcity or absence of saxitoxin. Considering the dominance of these toxins in each strain, at least two distinctive toxin patterns were distinguished. Through rDNA sequence analysis, the Chilean strains were segregated as part of Clade I (North American) of the Alexandrium tamarense species complex. Nevertheless, significant genetic diversity was also observed among the Chilean strains, especially using ITS sequences. Through these three approaches, Chilean strains of A. catenella showed significant intraregional variability, which is appropriate for a native species. However, the distribution of its genetic diversity seems to be inconsistent with the apparent northward expansion observed along the west coast of South America.     

Morphological diversity ofMortierella alpina: Effect of consumed carbon to nitrogen ratio in flask culture

The influence of the consumed carbon to nitrogen (C/N) ratio on mycelial morphology was investigated in cultures ofMortierella alpina using shake flasks. The consumed C/N ratio was varied from 5 to 32 under the condition that the total initial amount of the carbon and nitrogen sources was 50 g/L. The whole mycelia and filamentous mycelia exhibited no relationship with the consumed C/N ratio below a consumed C/N ratio of 20 in the presence of either excess carbon or excess nitrogen. However, when the consumed C/N ratio increased higher than 20, the mycelial sizes increased in proportion to the consumed C/N ratio. However, the area ratio of filamentous mycelia to total mycelia was found to be independent of the consumed C/N ratio, and remained constant at 0.82. In the case of a fixed consumed C/N ratio of 20, the whole mycelia and filamentous mycelia increased in proportion to the degree of the medium strength, yet the area ratio of filamentous mycelia to total mycelia remained unchanged at 0.76. Accordingly, these results show that fungal morphology and mycelial size are both affected by the ratio of carbon to nitrogen. The findings of the current study will be helpful in obtaining the efficient production of useful bioproducts from fungal cultures.     

Morphological properties ofSchizosaccharomyces pombe in a continuous culture

The dilution rate (specific growth rate) influences the mean volume ofS. pombe cells and their length—width ratio. The degree of asymmetry of the cell division is also a function of the dilution rare. The difference between the volume and length of both sibs of the dividing cell is significant under conditions of substrate limitation, whereas with excess substrate both parts of the cell are identical in volume.     

Flor yeast strains from culture collection: Genetic diversity and physiological and biochemical properties

Sixteen flor yeast strains from the Magarach Collection of the Microorganisms for Winemaking (Yalta, Crimea), which are used for production of sherry, were analyzed for morphophysiological, cultural, and biochemical properties. Long-term storage did not affect their viability or the preservation of major properties, such as their flor- and aldehyde-forming abilities, and the ability to produce wines with typical sherry properties. Significant variation in the strains was observed mainly in the aldehyde-forming and flor-forming abilities and flor properties. Interdelta typing was shown to be the most informative technique to study the genetic diversity of flor yeast strains. Certain correlations between genetic polymorphisms and the enological properties of the strains were observed. The presence of a 24-bp long deletion in the ITS1 spacer of the ribosomal gene cluster, a typical feature of Spanish flor yeast strains, is correlated with a high level of production of aldehydes and acetales, efficient flor formation, and the ability to produce high quality sherry. The presence of a specific deletion in the promoter of the FLO11 gene appeared to be less informative, since the aldehyde and acetal production and flor formation abilities of such strains were variable. The studies of intraspecies genetic polymorphism by various molecular markers have revealed a high degree of phylogenetic closeness of some yeast flor strains from different geographic regions.     

Morphological analysis of early contacts between pine roots and two ectomycorrhizal Suillus strains

 Selection of ectomycorrhizal strains for application in forestry is mostly based on the evaluation of symbiotic performance in small-scale experiments. Two Suillus collinitus strains isolated from a Mediterranean and an alpine area were inoculated onto two pine tree species (Pinus pinea and P. nigra ssp. laricio var. corsicana) typical of these two environments. The early events during contact between the cell surfaces of plant and fungal partners were analysed morphologically using ultrastructural and immunocytochemical techniques. All four plant-fungus combinations led to a similar degree of mycorrhizal infection and to a similar colonization pattern. The first contact of fungal hyphae with root cap cells usually involved breakdown of the outermost electron-opaque layer of the plant cell walls. Hyphae further developed between this layer and the underlying wall strata. Ultrastructural observations revealed that S. collinitus strain J3-15-24, isolated from a Mediterranean area, induced a defence reaction in the roots of P. nigra, which grows typically in alpine areas. These observations suggest functional differences between the two fungal strains in their mycorrhizal capabilities. Accepted: 3 April 1998     

Morphological diversity of androgenic carrot plants

The aim of this study was to evaluate phenotypic variation of R0 androgenic plants obtained from four seed sources and donor plants by anther culture. Several morphological traits (leaf size, petiole length, leaf division, cortex colour) and the range of diversity were evaluated. There was large variation in all traits among the donor varieties. Especially leaf division and cortex colour differed significantly among the androgenic plants that came from different seed sources. The plants regenerated from four donor plants of variety 62 were significantly different in most traits except for leaf width and cortex colour. Evaluation of R1 plants will demonstrate whether the R0 variation observed is due to genetic variation or physiological differences from tissue culture.     

Genetic diversity of Rhodopirellula strains

Rhodopirellula baltica SH1^T is a marine planctomycete with 7,325 genes in its genome. Ten strains of the genus Rhodopirellula were studied in whole genome microarray experiments to assess the extent of their genetic relatedness to R. baltica SH1^T. DNA of strains which were previously affiliated with the species R. baltica (OTU A) hybridized with 3,645–5,728 genes of the type strain on the microarray. Strains SH398 and 6C (OTU B), representing a closely related species with an average nucleotide identity of 88 %, showed less hybridization signals: 1,816 and 3,302 genes gave a hybridization signal, respectively. Comparative genomics of eight permanent draft genomes revealed the presence of over 4,000 proteins common in R. baltica SH1^T and strains of OTU A or B. The genus Rhodopirellula is characterized by large genomes, with over 7,000 genes per genome and a core genome of around 3000 genes. Individual Rhodopirellula strains have a large portion of strain-specific genes.     

有害赤潮生物球形棕囊藻对卤虫的毒性研究

利用1997年10月和1998年6月分别在广东汕头饶平海域和香港海域分离到的球形棕囊藻,即球形棕囊藻香港株(Phaeocystis globosastrain HK)和球形棕囊藻汕头株(Phaeocystis globosastrain ST),在实验室条件下研究其对四日龄卤虫(Artemia sinica)的急性毒性。结果表明,对数生长期的HK株藻液24h对卤虫LC₅₀约为2.9×10⁵cell·mL^-1。对数期的ST株对卤虫的毒性难以达到半致死浓度,衰亡期的ST株24h对卤虫LC₅₀约为9.89×10⁶cell·mL^-1。在上述浓度下两者半致死时间分别为20.91h和26.62h,而对数生长期的HK株和衰亡期的ST株的培养物过滤液24h对卤虫LC₅₀则分别为7.1×10⁵cell·mL^-1和1.457×10⁷cell·mL^-1,且在该浓度下的半致死时间分别为26.56h和28.02h。实验表明,HK株藻液和滤液的毒性均大于ST株,且藻液的毒性均大于滤液。