Alterations of Membrane Lipid Content Correlated With Chloroplast and Mitochondria Development in Euglena gracilis

Anti-algal activity of the 12-5-12 gemini surfactant results from its impact on the photosynthetic apparatus

A rapid amplification of algal population has a negative impact on the environment and the global economy. Thus, control of algal proliferation is an important issue and effective procedures which reduce algal blooms and control algal fouling are highly desired. Gemini surfactants are considered to have a low environmental impact, therefore they seem to be a promising group of detergents which could reduce algal blooms in water systems. Furthermore, due to their emulsifying properties they could replace algaecides added to antifouling paints and decrease algae adhesion to various surfaces. In this study the toxic effect of the 12-5-12 gemini surfactant was investigated on Chlorella cells and close attention was paid to a potential mechanism of its action. At the high cell density (10.05 × 10⁷ cells/mL) a dose-dependent cell death was found and the IC₅₀ value was reached at the concentration of 19.6 µmol/L after 72-h exposure to the surfactant. The decrease in chlorophyll autofluorescence shows that the photosynthetic apparatus seems to be the target of the tested compound. The presented studies indicate that gemini surfactants could effectively reduce algal blooms in water systems, and if added to paints, they could decrease algal growth on external building walls or other water immersed surfaces.

The Lipid Composition of Euglena gracilis Middle Plastid Membrane Resembles That of Primary Plastid Envelopes

Euglena gracilis is a photosynthetic flagellate possessing chlorophyte-derived secondary plastids that are enclosed by only three enveloping membranes, unlike most secondary plastids, which are surrounded by four membranes. It has generally been assumed that the two innermost E. gracilis plastid envelopes originated from the primary plastid, while the outermost is of eukaryotic origin. It was suggested that nucleus-encoded plastid proteins pass through the middle and innermost plastid envelopes of E. gracilis by machinery homologous to the translocons of outer and inner chloroplast membranes, respectively. Although recent genomic, transcriptomic, and proteomic data proved the presence of a reduced form of the translocon of inner membrane, they failed to identify any outer-membrane translocon homologs, which raised the question of the origin of E. gracilis's middle plastid envelope. Here, we compared the lipid composition of whole cells of the pigmented E. gracilis strain Z and two bleached mutants that lack detectable plastid structures, W10BSmL and WgmZOflL We determined the lipid composition of E. gracilis strain Z mitochondria and plastids, and of plastid subfractions (thylakoids and envelopes), using HPLC high-resolution tandem mass spectrometry, thin-layer chromatography, and gas chromatography-flame ionization detection analytical techniques. Phosphoglycerolipids are the main structural lipids in mitochondria, while glycosyldiacylglycerols are the major structural lipids of plastids and also predominate in extracts of whole mixotrophic cells. Glycosyldiacylglycerols were detected in both bleached mutants, indicating that mutant cells retain some plastid remnants. Additionally, we discuss the origin of the E. gracilis middle plastid envelope based on the lipid composition of envelope fraction.

Metabolic quirks and the colourful history of the Euglena gracilis secondary plastid

Euglena spp. are phototrophic flagellates with considerable ecological presence and impact. Euglena gracilis harbours secondary green plastids, but an incompletely characterised proteome precludes accurate understanding of both plastid function and evolutionary history. Using subcellular fractionation, an improved sequence database and MS we determined the composition, evolutionary relationships and hence predicted functions of the E. gracilis plastid proteome. We confidently identified 1345 distinct plastid protein groups and found that at least 100 proteins represent horizontal acquisitions from organisms other than green algae or prokaryotes. Metabolic reconstruction confirmed previously studied/predicted enzymes/pathways and provided evidence for multiple unusual features, including uncoupling of carotenoid and phytol metabolism, a limited role in amino acid metabolism, and dual sets of the SUF pathway for FeS cluster assembly, one of which was acquired by lateral gene transfer from Chlamydiae. Plastid paralogues of trafficking-associated proteins potentially mediating fusion of transport vesicles with the outermost plastid membrane were identified, together with derlin-related proteins, potential translocases across the middle membrane, and an extremely simplified TIC complex. The Euglena plastid, as the product of many genomes, combines novel and conserved features of metabolism and transport.

Influence of long term nitrogen limitation on lipid, protein and pigment production of Euglena gracilis in photoheterotrophic cultures

Nitrogen limitation is considered a good strategy for enhancement of algal lipid production while conversely N repletion has been shown to result in biomass rich in proteins. In this study, the influence of long-term N limitation on Euglena gracilis fatty acid (FA), protein, chlorophyll a, and carotenoid concentrations was studied in N limited cultures. Biomass composition was analyzed from three-time points from N starved late stationary phase cultures, exposed to three different initial N concentrations in the growth medium. Total lipid content increased under N limitation in ageing cultures, but the low N content and prolonged cultivation time resulted in the formation of a high proportion of saturated FAs. Furthermore, growth as well as the production of proteins, chlorophyll a and carotenoids were enhanced in higher N concentrations and metabolism of these cellular components stayed stable during the stationary growth phase. Our findings showed that a higher N availability and a shorter cultivation time is a good strategy for efficient E. gracilis biomass production, regardless of whether the produced biomass is intended for maximal recovery of polyunsaturated FAs, proteins, or photosynthetic pigments. Additionally, we showed an increase of neoxanthin, β-carotene, and diadinoxanthin as a response to higher N availability.