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Nannochloropsis is a genus of eicosapentaenoic acid-rich microalgae with high levels of value-added polar lipids. However, the polar lipid composition of microalgal biomass is highly dependent on culture conditions (e.g., light or temperature), which are significantly different under indoor and outdoor culture conditions. In this study, we sought to investigate the plasticity of the polar lipid profile of a marine (N. oceanica) and a freshwater (N. limnetica) species of Nannochloropsis grown in indoor and outdoor photobioreactors. To this end, the polar lipidome and fatty acid profiles were characterized by liquid chromatography-mass spectrometry (LC-MS), and gas chromatography-mass spectrometry (GC-MS), respectively. In addition, the antioxidant activity of their lipid extracts was assessed. The highest lipid contents were obtained for the two species grown indoors. LC-MS analysis identified 239 different polar lipid species, of which 220 were shared by all experimental groups. Candidate lipid biomarkers from both culture systems were proposed, including MGDG(34:2), MGDG(34:1) and PG(36:6). For both species, indoor conditions lead to lipid extracts rich in glycolipids and higher in oleic acid content. In contrast, outdoor conditions lead to higher proportions of phospholipids and betaine lipids and a higher relative content of eicosapentaenoic acid (EPA). The polar lipid profile of the two Nannochloropsis species differed primarily in the relative amounts of certain betaine lipids, mainly DGTS (which was increased in N. oceanica) and lysolipids (LPC, and LPE) (increased in N. limnetica), although the majority of lipids were observed in both species. The lipid extracts showed antioxidant activity (IC15) ranging from 30.4 +/- 1.8 to 45.7 +/- 1.6 mu mol Trolox g-1 of lipid extract. Overall, this study provides insight into the lipid metabolic adaptation of two Nannochloropsis species, providing the know-how to obtain a healthy polar lipid-rich biomass useful for novel applications in pharmaceutical, nutraceutical, or novel foods. info:eu-repo/semantics/publishedVersion

The microalgal genus of Nannochloropsis is considered one of the most promising organisms for the production of biofuels due to their high lipid content. Transformation systems for marine Nannochloropsis species have been established in the recent decade, however, genetic manipulation of Nannochloropsis limnetica, the only known freshwater species in this genus, is not yet available. Based on established marine Nannochloropsis species electrotransformation protocol, nuclear genetic transformation was established in N. limnetica, meanwhile the appropriate antibiotic selection concentration and electric field strength of electroporation were determined. For the selection of transformants in N. limnetica on plates, 0.07 μg mL-1 of zeocin or 5 μg mL-1 of hygromycin B was proved sufficient, and the transformation efficiency was

Algae of the genus Nannochloropsis are attractive organisms for use in biotechnology due to their high lipid content. Genetic manipulation of marine Nannochloropsis species has already been reported; however, tools have not yet been developed to transform Nannochloropsis limnetica, the only known freshwater species of this genus. To establish N. limnetica as a model laboratory strain, we first tested the effects of 11 different antibiotics on growth of N. limnetica and the marine species N. oceanica and N. gaditana. These three microalgae responded very differently to antibiotic treatments, both in liquid cultures and on agar plates. In general, N. limnetica exhibited a much higher sensitivity to antibiotics than the marine strains, thus offering the potential for a large set of antibiotic resistance genes that may be applicable as artificial selection markers after transformation. We also developed a simple protocol using lysozyme to obtain high yields of viable N. limnetica protoplasts, as confirmed by flow cytometry and electron microscopy.

Three new strains of eukaryotic picoplankton, isolated from Lake Baikal, were identified as Nannochloropsis limnetica Krienitz, Hepperle, Stich & Weiler. To date, N. limnetica had only been detected in small German and North American inland water bodies. On determination of the 18S rDNA sequence, the three new strains were found to be identical to each other and to the type strain KR 1998/3 (GenBank accession no. AF251496). Rapid analysis of polymorphic DNA-PCR revealed that the genotypes were different, although the Baikalian eustigmatophycean strains were more similar to each other compared with the type strain KR 1998/3 from Germany. Ecophysiological differences were also evident between the new strains from Lake Baikal and the type strain from growth rate determinations. The morphological characteristics were similar to that of a previous description of the species. However, although the cells of Eustigmatophyceae usually propagate by autosporulation, in these newly detected species germination of single daughter cells from thick-walled cells was observed for the first time. Based on pigment analysis, the occurrence of Eustigmatophyceae in Lake Baikal was estimated. Eustigmatophyceae were established to be common members of the phytoplankton community of this large oligotrophic Siberian lake and occurred throughout the year, even under the ice cover during winter. Moreover, they peaked during early summer and in the South Basin. Hence, the widely accepted opinion that Chlorophyceae solely comprise the eukaryotic picoplankton should be changed and the Eustigmatophyceae considered.

Empirical data providing evidence for a colimitation of an herbivore by two or more essential nutrients are scarce, particularly in regard to biochemical resources. Here, a graphical model is presented, which describes the growth of an herbivore in a system with two potentially limiting resources. To verify this model, life-history experiments were conducted with the herbivore Daphnia magna feeding on the picocyanobacterium Synechococcus elongatus , which was supplemented with increasing amounts of cholesterol either in the presence or the absence of saturating amounts of eicosapentaenoic acid (EPA). For comparison, D. magna was raised on diets containing different proportions of S. elongatus and the cholesterol- and EPA-rich eukaryotic alga Nannochloropsis limnetica . Somatic and population growth of D. magna on a sterol- and EPA-deficient diet was initially constrained by the absence of sterols. With increased sterol availability, a colimitation by EPA became apparent and when the sterol requirements were met, the growth-limiting factor was shifted from a limitation by sterols to a limitation by EPA. These data imply that herbivores are frequently limited by two or more essential nutrients simultaneously. Hence, the concept of colimitation has to be incorporated into models assessing nutrient-limited growth kinetics of herbivores to accurately predict demographic changes and population dynamics.