Phylogenomic analyses of ochrophytes (stramenopiles) with an emphasis on neglected lineages.

Ochrophyta is a photosynthetic lineage that crowns the phylogenetic tree of stramenopiles, one of the major eukaryotic supergroups. Due to their ecological impact as a major primary producer, ochrophytes are relatively well-studied compared to the rest of the stramenopiles, yet their evolutionary relationships remain poorly understood. This is in part due to a number of missing lineages in large-scale multigene analyses, and an apparently rapid radiation leading to many short internodes between ochrophyte subgroups in the tree. These short internodes are also found across deep-branching lineages of stramenopiles with limited phylogenetic signal, leaving many relationships controversial overall. We have addressed this issue with other deep-branching stramenopiles recently, and now examine whether contentious relationships within the ochrophytes may be resolved with the help of filling in missing lineages in an updated phylogenomic dataset of ochrophytes, along with exploring various gene filtering criteria to identify the most phylogenetically informative genes. We generated ten new transcriptomes from various culture collections and a single-cell isolation from an environmental sample, added these to an existing phylogenomic dataset, and examined the effects of selecting genes with high phylogenetic signal or low phylogenetic noise. For some previously contentious relationships, we find a variety of analyses and gene filtering criteria consistently unite previously unstable groupings with strong statistical support. For example, we recovered a robust grouping of Eustigmatophyceae with Raphidophyceae-Phaeophyceae-Xanthophyceae while Olisthodiscophyceae formed a sister-lineage to Pinguiophyceae. Selecting genes with high phylogenetic signal or data quality recovered more stable topologies. Overall, we find that adding under-represented groups across different lineages is still crucial in resolving phylogenetic relationships, and discrete gene properties affect lineages of stramenopiles differently. This is something which may be explored to further our understanding of the molecular evolution of stramenopiles.

Comprehensive Lipidomic Analysis of Three Edible Microalgae Species Based on RPLC-Q-TOF-MS/MS.

Microalgae, integral to marine ecosystems for their rich nutrient content, notably lipids and proteins, were investigated by using reversed-phase liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (RPLC-Q-TOF-MS/MS). This study focused on lipid composition in three commonly used microalgae species (Spirulina platensis, Chlorella vulgaris, and Schizochytrium limacinum) for functional food applications. The analysis unveiled more than 700 lipid molecular species, including glycolipids (GLs), phospholipids (PLs), sphingolipids (SLs), glycerolipids, and betaine lipids (BLs). GLs (19.9-64.8%) and glycerolipids (24.1-70.4%) comprised the primary lipid. Some novel lipid content, such as acylated monogalactosyldiacylglycerols (acMGDG) and acylated digalactosyldiacylglycerols (acDGDG), ranged from 0.62 to 9.68%. The analysis revealed substantial GLs, PLs, and glycerolipid variations across microalgae species. Notably, S. platensis and C. vulgaris displayed a predominance of fatty acid (FA) 18:2 and FA 18:3 in GLs, while S. limacinum exhibited a prevalence of FA 16:0, collectively constituting over 60% of the FAs of GLs. In terms of PLs and glycerolipids, S. platensis and C. vulgaris displayed elevated levels of arachidonic acid (AA) and eicosapentaenoic acid (EPA), whereas S. limacinum exhibited a significant presence of docosahexaenoic acid (DHA). Principal component analysis (PCA) revealed MGDG (16:0/18:1), DG (16:0/22:5), Cer (d18:1/20:0), and LPC (16:1) as promising lipid markers for discriminating between these microalgae samples. This study contributes to a comprehensive understanding of lipid profiles in three microalgae species, emphasizing their distinct biochemical characteristics and potentially informing us of their high-value utilization in the food industry.

Isolation and molecular characterization of Thraustochytrium strain isolated from Antarctic Peninsula and its biotechnological potential in the production of fatty acids

ABSTRACT Thraustochytrids are unicellular protists belonging to the Labyrinthulomycetes class, which are characterized by the presence of a high lipid content that could replace conventional fatty acids. They show a wide geographic distribution, however their diversity in the Antarctic Region is rather scarce. The analysis based on the complete sequence of 18S rRNA gene showed that strain 34-2 belongs to the species Thraustochytrium kinnei, with 99% identity. The total lipid profile shows a wide range of saturated fatty acids with abundance of palmitic acid (16:0), showing a range of 16.1-19.7%. On the other hand, long-chain polyunsaturated fatty acids, mainly docosahexaenoic acid and eicosapentaenoic acid are present in a range of 24-48% and 6.1-9.3%, respectively. All factors analyzed in cells (biomass, carbon consumption and lipid content) changed with variations of culture temperature (10 °C and 25 °C). The growth in glucose at a temperature of 10 °C presented the most favorable conditions to produce omega-3fatty acid. This research provides the identification and characterization of a Thraustochytrids strain, with a total lipid content that presents potential applications in the production of nutritional supplements and as well biofuels.