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Abstract Microalgae accumulate neutral lipids in oil bodies under sulfur-starvation conditions, and determination of the molecular basis of lipid accumulation under sulfur-starvation conditions will enable improvement of the production of biofuel. We analyzed two l -cysteine dependent mutants (Srp1 and Srp2) of the green alga Parachlorella kessleri. The wild-type cells accumulated lipids and developed oil bodies under sulfate-depleted conditions but not under sulfate-replete conditions. Srp1 and Srp2 showed suppressed proliferation and lipid and starch accumulation under sulfate-replete conditions but accumulated only lipids under sulfate-depleted conditions. Although the suppressed cell proliferation of the mutants was partially complemented in medium containing l -cysteine as a sulfur source, that of the wild type was completely complemented, and lipids did not accumulate in the wild type or the mutants. Our results suggest that the accumulation of lipids in P. kessleri under sulfate-depleted conditions results from a shortage of sulfate metabolites, such as l -cysteine, and that sulfate promotes starch accumulation. Highlights • Mutants of the green alga Parachlorella kessleri requires l -cysteine for proliferation. • The mutants exhibit not only lipid but also starch accumulation under sulfate-replete conditions. • A shortage of sulfate metabolites and sulfate promotes lipid accumulation and starch accumulation, respectively. [ABSTRACT FROM AUTHOR]

Abstract Parachlorella kessleri (formerly Chlorella kessleri) can accumulate high levels of both starch and lipids that can be used for the production of bioethanol and biodiesel, respectively. We mutagenized P. kessleri by heavy-ion beam irradiation and obtained a biotechnologically promising mutant strain, PK4, for further improvement of lipid productivity in comparison with wild type [1]. PK4 reached two times the optical density and accumulated 2.6 times as much starch in complete urea-phosphate (UP) media compared to tris-acetate-phosphate (TAP) media under laboratory conditions. Similarly to wild type, PK4 accumulated only negligible amounts of lipids in complete UP media. PK4 accumulated more lipids (WT: 1.17 g L−1, PK4: 1.75 g L−1) and accumulated lipids faster than WT after dilution of the UP media (WT; 0.22 g L−1 day−1, PK4; 0.43 g L−1 day−1). The productivity of PK4 was analyzed in mass culture using a 150-L thin-layer photo bioreactor housed in a temperature and light-uncontrolled glass greenhouse. The PBR consisted of two glass plates (each 6 m long and 1 m wide) at an inclination of 1.6%, arranged in a meandering path and connected with a trough. The culture was diluted four-fold with water on day 7 post-inoculation to ensure prompt nutrient limitation in the UP media. Lipid accumulation in PK4 was significantly induced so that it accumulated 66% of lipid per dry weight. Under 150-L mass cultivation conditions, PK4 showed high biomass productivity (0.82 g L−1 day−1) and high lipid productivity (0.59 g L−1 day−1). In addition, the whole genome of PK4 was sequenced to clarify the genetic variation upon heavy-ion-beam irradiation by comparison with the reference genome of WT. As a result, genetic differentiation of PK4 was found at three genes encoding endo-1,4-β-mannanase, an ATP/ADP transporter, and an elicitor response protein. Highlights • PK4 is a heavy-ion beam irradiation mutant isolated from Parachlorella kessleri. • PK4 accumulated more lipids and faster than WT in diluted urea-phosphate (UP) media. • Its maximum lipid content was 66% per DW using a thin-layer photo bioreactor (150-L). • PK4 achieved high biomass and lipid productivity in the 150-L mass cultivation. • Genetic differentiation of PK4 was found at three genes such as endo-1,4-β-mannanase. [ABSTRACT FROM AUTHOR]

Biological treatments using microalgae represent an environmental-friendly approach to the decontamination of coking wastewater, which contains toxic levels of ammonium; however, few algal species can tolerate such high ammonium levels. In this study, we investigated the morphology, ultrastructure, molecular phylogeny, and physiological characteristics of Parachlorella kimitsuensis sp. nov., a new algal species with high ammonium tolerance. This species was isolated from coking wastewater obtained near a steelworks factory, where the ratio of nitrogen to phosphorus (N/P) exceeded 40, approximately 100-fold that of general culture medium. The growth inhibition test estimated that the effective concentration at 10 % inhibition (EC 10) was 3.2 ppm NH 4 +-N, and the half maximal effective concentration (EC 50) was 98.0 ppm NH 4 +-N, indicating tolerance to fairly high concentrations of ammonium in this species. Parachlorella kimitsuensis has spherical, green cells resembling those of Chlorella species. The major diameter of the cells was 3.7 ± 0.39 μm; cells containing eight autospores appearing in the early logarithmic growth phase were 6.9 ± 0.78 μm in diameter. Molecular phylogenetic analysis showed that the alga was a member of the genus Parachlorella , with 100 % bootstrap support. However, the results of vegetative cell morphology and phylogenetic analyses using 18S rRNA genes were inconsistent with those of other described Parachlorella species. Therefore, we identified the isolate as a new species in the genus Parachlorella. We anticipate that this species will be suitable for biological treatment of wastewater containing high ammonium levels, such as coking wastewater. • A new strain of Parachlorella isolated from coking wastewater • Adapted to highly ammonium and salinity of seawater • Potential for biological treatment of wastewater containing ammonium [ABSTRACT FROM AUTHOR]

The type of Haematococcus Flot. (Volvocales, Chlorophyceae) accumulates astaxanthin in its dormant stage. Currently, only one species is recognized in the genus; however, it is referred to by two names: H. lacustris (Gir.‐Chantr.) Rostaf. and H. pluvialis Flot. This confusion arose partly because of misunderstanding over the nomenclature and partly because of inadequate descriptions of Volvox lacustris Gir.‐Chantr. and H. pluvialis. Here, we designate an epitype based on a single cryopreserved culture that supports the newly designated lectotype of V. lacustris. Our treatment objectively synonymizes the two names and designates the correct name for the type of Haematococcus as H. lacustris, not H. pluvialis. In addition, we provide light microscopy descriptions and ITS rDNA information regarding the strain related to the epitype. [ABSTRACT FROM AUTHOR]

A culture of Thaumatomastix was isolated from a sediment sample collected in Oslofjorden and established as a monospecific strain (UIO286). Based on this culture, light and transmission electron microscopy and phylogenetic analyses were carried out. Thaumatomastix species are confined within the order Thaumatomonadida of the class Imbricatea and phylum Cercozoa. They are heterotrophic and their cell bodies are covered with silica scales. Observations of thin sections as well as whole mounts indicate that the morphology and ultrastructure of UIO286 is identical to T. salina, which was initially described from salt pools in Denmark. Detailed examination revealed some new features such as the presence of pseudopodia and silica deposition vesicles producing spine scales. The phylogeny presented here includes ribosomal DNA sequences from both imbricatean cultures and environmental samples. The 18S rDNA phylogenetic tree suggests that (i) Thaumatomastix is paraphyletic within the Thaumatomonadida clade, (ii) there is no close affinity between T. salina and other cultured and sequenced strains, but it is closely related to a sequence obtained from environmental DNA; we propose the present strain to serve as a reference culture of Thaumatomastix species and T. salina. Further, we discuss the distribution, habitats, and evolution of scale formation among euglyphids and thaumatomonads. [ABSTRACT FROM AUTHOR]

A culture of Thaumatomastix was isolated from a sediment sample collected in Oslofjorden and established as a monospecific strain (UIO286). Based on this culture, light and transmission electron microscopy and phylogenetic analyses were carried out. Thaumatomastix species are confined within the order Thaumatomonadida of the class Imbricatea and phylum Cercozoa. They are heterotrophic and their cell bodies are covered with silica scales. Observations of thin sections as well as whole mounts indicate that the morphology and ultrastructure of UIO286 is identical to T. salina , which was initially described from salt pools in Denmark. Detailed examination revealed some new features such as the presence of pseudopodia and silica deposition vesicles producing spine scales. The phylogeny presented here includes ribosomal DNA sequences from both imbricatean cultures and environmental samples. The 18S rDNA phylogenetic tree suggests that (i) Thaumatomastix is paraphyletic within the Thaumatomonadida clade, (ii) there is no close affinity between T. salina and other cultured and sequenced strains, but it is closely related to a sequence obtained from environmental DNA; we propose the present strain to serve as a reference culture of Thaumatomastix species and T. salina. Further, we discuss the distribution, habitats, and evolution of scale formation among euglyphids and thaumatomonads. [ABSTRACT FROM AUTHOR]

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 9-16μm 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. [Copyright &y& Elsevier]

A new chlorarachniophyte, Partenskyella glossopodia gen. et sp. nov., is described from a culture isolated from the Mediterranean Sea pelagic waters and maintained as strain RCC365 at the Roscoff Culture Collection (France). Vegetative cells of P. glossopodia are non-motile naked spherical cells. However, flagellate and amoeboid stages are also present in its life cycle. The cells are 2–4μm in diameter containing a pale-green, cup-shaped chloroplast, 1–2 mitochondria, a nucleus, and a Golgi apparatus. Vesicles containing storage product-like material are also present. The chloroplast is surrounded by four membranes possessing a nucleomorph in the periplastidal compartment. The minute cell size and the absence of a pyrenoid at any stage of the life cycle are unique characteristics among the chlorarachniophytes, which justifies our proposition for a new genus for strain RCC365. [Copyright &y& Elsevier]