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Strain HS-399 was isolated from a mangrove swamp in Biscayne Bay (Florida, USA) and selected for its capacity to accumulate lipids (84.0±1.0% DW), particularly docosahexaenoic acid (DHA; 22:6 n-3) (28.3±0.1% DW). Molecular phylogenetic analysis demonstrated that the new organism belonged to the genus Aurantiochytrium, and when the whole nuclear genome was blasted against the type species (and only described species), A. limacinum SR21, there was a 5.38% difference at the protein level. We described our new organism as Aurantiochytrium acetophilum sp. nov. (Thraustochytriaceae, Thraustochytriales) using light microscopy, electron microscopy, substrate assimilation, biochemical composition and nuclear genomic data. We found some characteristics of biotechnological relevance that were not previously described in this family. First, strain HS-399 of A. acetophilum was extremely tolerant to acetate toxicity, and it used this substrate as a sole carbon source. Second, we observed putative gametes that fused together to form a zygote. Zygote fate and the life stage with meiosis were not determined; however, we found several meiosis genes in the genome, further supporting the possibility of breeding for these industrially relevant organisms., (Copyright © 2019 Heliae Development LLC. Published by Elsevier GmbH.. All rights reserved.)

Heterosigma akashiwo is a raphidophyte known for forming ichthyotoxic blooms. In order to predict the potential impacts of rising CO 2 on H. akashiwo it is necessary to understand the factors influencing growth rates over a range of CO 2 concentrations. Here we examined the physiology and gene expression response of H. akashiwo to concentrations from 200 to 1000ppm CO 2 . Growth rate data were combined from this and previous studies and fit with a CO 2 limitation-inhibition model that revealed an apparent growth optimum around 600-800ppm CO 2 . Physiological changes included a significant increase in C:N ratio at ∼800ppm CO 2 and a significant decrease in hydrogen peroxide concentration at ∼1000ppm. Whole transcriptome sequencing of H. akashiwo revealed sharp distinctions in metabolic pathway gene expression between ∼600 and ∼800ppm CO 2 . Hierarchical clustering by co-expression identified groups of genes with significant correlations to CO 2 and growth rate. Genes with significant differential expression with CO 2 included carbon concentrating mechanism genes such as beta-carbonic anhydrases and a bicarbonate transporter, which may underpin shifts in physiology. Genes involved in cell motility were significantly changed by both elevated CO 2 and growth rate, suggesting that future ocean conditions could modify swimming behavior in this species., (Copyright © 2018 Elsevier GmbH. All rights reserved.)

Thraustochytrid cells attach to their food via ectoplasmic nets (ENs). Here, we analyzed the cause and effect relationship between the various forms and functions of ENs of Schizochytrium aggregatum. The ENs spread out over a large area forming a fine network to efficiently search for the experimental food source. After recognizing the experimental food source, the ENs that attached to the food source became thicker, and net elements developed. The thick ENs on the surface at the attachment site were enveloped in dense materials (fibrous materials), which were visualized as fibrous layers under a transmission electron microscope. Experiments using fluorescein diacetate and the fluorescent glucose analog 2-NBDG showed that the production rate of hydrolytic enzymes and the absorption rate of glucose by ENs of S. aggregatum increased in the presence of an experimental food source. Our results reveal that ENs change their shape and function according to the presence/absence of a food source., (Copyright © 2018 Elsevier GmbH. All rights reserved.)

F-actin organization during the cell cycle was investigated in two stramenopile microalgae, Ochromonas danica (Chrysophyceae; UTEX LB1298) and Heterosigma akashiwo (Raphidophyceae; NIES-6) using FITC-phalloidin. In the interphase cell of O. danica, F-actin bundles were localized forming a network structure in the cortical region, which converged from the anterior region to the posterior, whereas in the interphase cell of H. akashiwo, F-actin bundles were observed forming a network structure in the cortical region without any polarity. In both O. danica and H. akashiwo, at the initial stage of mitosis the cortical F-actin disappeared, and then during cytokinesis assembly of an actin-based ring-like structure occurred in the cell cortex in the plane of cytokinesis. The ring-like structure initiated from aster-like structures was composed of F-actin in both O. danica and H. akashiwo. Different from animal cells, later stages of cytokinesis of O. danica seemed to be promoted by microtubules, although the early stages of cytokinesis progressed with a constriction of the ring-like structure, whereas cytokinesis of H. akashiwo was apparently completed by constriction of the cell mediated by the F-actin ring, as in animal cells., (Copyright © 2011 Elsevier GmbH. All rights reserved.)