Parietochloris incisa comb. nov. (Trebouxiophyceae, Chlorophyta)

A coccoid green alga, Myrmecia incisa Reisigl, was isolated from the soil of Mt Tateyama, Japan. Electronmicroscopy revealed that the organism has pyrenoids sparsely covered with starch segments and traversed by many parallel thylakoid membranes, and zoo-spores with counterclockwise basal body orientation. Due to the presence of these features, we have proposed a reclassification of M. incisa into the genus Parietochloris, Trebouxiophyceae.     

Phylogenetic relationships of green algae assigned to the genus Planophila (Chlorophyta): evidence from 18S rDNA sequence data and ultrastructure

Phylogenetic analyses, based upon nuclear small-subunit ribosomal RNA gene sequences, of four ‘chlorosarcinoid’ species referred to Planophila Gerneck show that the genus is polyphyletic. The type species, P. laetevirens Gerneck, is closely related to species in the Ulotrichales, Ulvophyceae. The monotypic sarcinoid genus Pseudendocloniopsis is the closest relative of Planophila; the two genera represent the addition of a new morphological type to the Ulotrichales. Planophila microcystis (Dangeard) Kornmann & Sahling forms a clade at the base of the Ulvophyceae with Oltmannsiellopsis, and thus belongs to the Oltmannsiellopsidales. This result is also supported by the Oltmannsiellopsis-like ultrastructure of P. microcystis zoospores. Planophila sp. B from Antarctica, which has Trebouxia-like pyrenoid structure, is a trebouxiophyte closely related to Chlorella-like unicellular coccoids, Stichococcus bacillaris and Prasiola species. This is the first robustly supported molecular phylogenetic analysis that places Prasiola in the Trebouxiophyceae. As shown previously, P. terrestris Groover & Hofstetter belongs to the Chaetopeltidales, Chlorophyceae. Dangemannia gen. nov. (type species : D. microcystis (Dangeard) comb. nov.), Floydiella gen. nov. (type species : F. terrestris (Groover & Hofstetter) comb. nov.) and Pabia gen. nov. (type: P. signiensis sp. nov.) are proposed.     

Protective role of 20-hydroxyecdysone against lead stress in Chlorella vulgaris cultures

Treatment of cultured C. vulgaris cells with 10(-6)-10(-4) M lead decreased their growth and chemical composition during the first 48 h of cultivation. However, at concentrations above 10(-4) M, lead is cytotoxic to Chlorella vulgaris cells, resulting in cellular fragmentation and lysis. In contrast, at concentrations below 10(-6) M lead had no influence on the growth and metabolism of C. vulgaris cells. 20-Hydroxyecdysone (20E) (10(-10)-10(-8) M) increased growth and chemical composition of C. vulgaris cells over a concentration range. Levels per cell of chlorophylls, protein, sugars are all increased by 20E treatment, when compared to non-treated control cells. However, the cultures treated with 20E and lead show a lower stimulation than the cultures treated with 20E alone. The effects of 20E mixed with lead on the growth and the level of cellular lead, chlorophyll, sugar and protein in C. vulgaris are also reported. The decreased growth and composition of C. vulgaris cells treated with lead was restored by the 20E. Application of 20E to C. vulgaris cultures reduced the impact of lead stress on growth, prevented chlorophyll, sugar and protein loss and increased phytochelatins synthesis. Furthermore, 20E did not restore toxic effect of lead on C. vulgaris cells. The combined treatment with lead and 20E appeared to have a stimulatory effect on the above parameters during the 48 h of cultivation, as compared to the control. 20E reduced the toxicity of lead and the growth recovered to the level of cells treated with 20E alone. Concentration-dependent stimulation was observed with increasing concentration of 20E and decreasing concentration of lead.     

Origin and evolution of chloroplast group I introns in lichen algae

The history of group I introns is characterized by repeated horizontal transfers, even among phylogenetically distant species. The symbiogenetic thalli of lichens are good candidates for the horizontal transfer of genetic material among distantly related organisms, such as fungi and green algae. The main goal of this study was to determine whether there were different trends in intron distribution and properties among Chlorophyte algae based on their phylogenetic relationships and living conditions. Therefore, we investigated the occurrence, distribution and properties of group I introns within the chloroplast LSU rDNA in 87 Chlorophyte algae including lichen and free‐living Trebouxiophyceae compared to free‐living non‐Trebouxiophyceae species. Overall, our findings showed that there was high diversity of group I introns and homing endonucleases (HEs) between Trebouxiophyceae and non‐Trebouxiophyceae Chlorophyte algae, with divergence in their distribution patterns, frequencies and properties. However, the differences between lichen Trebouxiophyceae and free‐living Trebouxiophyceae were smaller. An exception was the cL2449 intron, which was closely related to ω elements in yeasts. Such introns seem to occur more frequently in lichen Trebouxiophyceae compared to free‐living Trebouxiophyceae. Our data suggest that lichenization and maintenance of lichen symbiosis for millions of years of evolution may have facilitated horizontal transfers of specific introns/HEs between symbionts. The data also suggest that sequencing of more chloroplast genes harboring group I introns in diverse algal groups may help us to understand the group I intron/HE transmission process within these organisms.     

Isolation and characterization of brassinosteroids from algal cultures of Chlorella vulgaris Beijerinck (Trebouxiophyceae)

The brassinosteroids (BRs) occur ubiquitously in the plant kingdom. The occurrence of BRs has been demonstrated in almost every part of higher plants, such as pollen, flower buds, fruits, seeds, vascular cambium, leaves, shoots and roots. In this study, BRs were isolated and identified in the culture of wild-type Chlorella vulgaris. Seven BRs, including teasterone, typhasterol, 6-deoxoteasterone, 6-deoxotyphasterol, 6-deoxocastasterone, castasterone and brassinolide, were identified by GC–MS. All compounds belong to the BR biosynthetic pathway. The results suggest that early and late C6 oxidation pathways are operating in C. vulgaris. This study represents the first isolation of BRs from C. vulgaris cultures.     

Small‐scale variation of corticolous microalgal covers: Effects of microhabitat,season, and space

The present study focuses on temporal and microscale spatial variation of the community structure and richness of subaerial microalgae growing on the bark of European beech (Fagus sylvatica) trees in temperate deciduous forests. Subaerial phototrophic biofilms present common and conspicuous microalgal communities growing on a variety of natural and man‐made substrata. However, in comparison with other major microalgal communities such as phytoplankton and microphytobenthos, basic patterns of their spatio‐temporal variation remain largely unknown. The bark samples were collected six times each spring and autumn in a period of 3 years (2010–2013) and were cultured on agar plates, and then individual clonal strains were identified by light microscopy. A total of 55 morphotypes (considered as operational taxonomic units for subsequent analyses) were recognized, which mainly belong to the classes Trebouxiophyceae and Chlorophyceae. Interestingly, temporal variation explained the largest proportion of variation in the community structure. This variation was primarily related to seasonal fluctuations, and although the communities recorded in spring and autumn showed many overlapping taxa, a clear distinction in species composition and abundance was observed. However, the microhabitat characteristics such as bark roughness also significantly structured the microalgal community. Conversely, spatial factors such as the height of the samples above ground or distance of the samples on a trunk seemed to be of lesser importance on this scale. Thus, we concluded that the previously unrecognized seasonal changes, resulting from variation in temperature, humidity, and irradiance, as well as the non‐seasonal temporal changes, possibly resulting from local colonization or extinction of individual taxa, should be considered as one of the important factors in structuring aerial microalgal communities.     

MARINICHLORELLA KAISTIAE GEN. ET SP. NOV. (TREBOUXIOPHYCEAE,CHLOROPHYTA) BASED ON POLYPHASIC TAXONOMY1

We describe three coccoid green algal strains belonging to a new genus and species, Marinichlorella kaistiae Z. Aslam, W. Shin, M. K. Kim, W.‐T. Im et S.‐T. Lee, in seawater samples from the South Sea of Korea. These strains were maintained at 25°C–30°C under a 12:12 light:dark (L:D) photoregime in an ASN‐III medium at a pH of 7.5. These strains were tolerant of high salinity (7.5% NaCl) (w/v) and temperature (40°C). Molecular phylogenetic analyses using 18S rRNA gene sequence data resolved these organisms to a clade separate from green coccoid algae with similar morphology. The DNA–DNA hybridization results demonstrated very low relatedness of these organisms to phylogenetically related species of the genera Chlorella and Parachlorella. The molar guanine + cytosine content (G + C mol%) of the genomic DNA of these organisms ranged from 64.7 to 69.1 mol%. Based on molecular phylogeny, DNA–DNA hybridization, and other morphological studies, we propose a new taxon, Marinichlorella kaistiae, to describe these strains and classify them in the family Chlorellaceae. The type strain is KAS007^T (= KCTC AG10303^T = IAM C‐620^T).