Differences in betaine lipids and fatty acids between Pseudoisochrysis paradoxa VLP and Diacronema vlkianum VLP isolates (Haptophyta)

Two Haptophytes were isolated from extensive aquaculture ponds at Veta La Palma state (Guadalquivir estuary, SW Spain). They were identified as Pseudoisochrysis paradoxa VLP and Diacronema vlkianum VLP based on their SSU rDNA homology to other Haptophytes and positioned in the Isochrysidaceae and Pavlovaceae families, respectively. Both Haptophytes had phosphatidilglycerol (PG) as the only phospholipid (PL), representing a low proportion of the total lipid content (0.8% in P. paradoxa VLP and 3.3% in D. vlkianum VLP). Instead, they were found to have different types of betaine lipids (BL) that were identified and characterized by HPLC/ESI-TOF-MS operating in multiple reacting monitoring (MRM) modes. P. paradoxa VLP had 2.2% of total lipids as diacylgyceryl-N-trimethylhomoserine (DGTS): it is the first Haptophyte reported to have this BL. Its total lipid fraction also contained 12.0% of diacylglyceryl-carboxyhydroxymethylcholine (DGCC) as the main BL and no diacylglyceryl-hydroxymethyl-N,N,N-trimethyl-β-alanine (DGTA) was detected. DGTA was only present (4.6% of total lipids) in D. vlkianum VLP: this was the main difference in BL content relative to P. paradoxa. D. vlkianum VLP also had DGTS (4.1%) and DGCC (7.6%): it is the first microalgae in which the simultaneous presence of these three BL has been demonstrated.The fatty acid profiles of P. paradoxa VLP and D. vlkianum VLP were close to those described for the major part of known members of the Isochrisidaceae and Pavlovaceae families, respectively, with the main differences due to the higher percentages of 18:1n9 (18.5%), 18:4n3 (12.6%) and 22:6n3 (9.3%) in the former. The corresponding fatty acid percentages for D. vlkianum VLP were 3.9%, 3.5% and 3.9%, respectively. D. vlkianum VLP showed higher 16:1n7 (16.1%) and 20:5n3 (9.4%) contents, whereas P. paradoxa VLP had significantly lower percentages of 16:1n7 (1.7%) and 20:5n3 (0.6%). Fatty acids of BL differed between both haptophytes. In DGTS from P. paradoxa VLP, 90.9% of total molecular species consisted of the 14:0–18:1 fatty acid combination, whereas DGTS from D. vlkianum showed a more diverse range of fatty acids. The unsaturation index (UI) of DGTS was lower (55.8) than that of total lipid UI (178.3) in P. paradoxa VLP. In D. vlkianum VLP the UI of DGTS was higher (146.9) and similar to that for total cell lipids (145.9). DGTA from D. vlkianum VLP had the highest UI (321.8) of all BL studied and it contained maximum levels (27.7%) of 22:6n3, representing 7.1 times the proportion of this fatty acid in the whole lipid extract. DGCC was enriched in 20:5n3 by a factor of around four in both microalgae. Due to different levels of this fatty acid in the two microalgae their respective 20:5n3 content in DGCC varied from 2.2% (P. paradoxa VLP) to 41.0% (D. vlkianum VLP) and these concentrations were also associated with UI values of 92.2 and 271.0, respectively. The specific differences in BL and fatty acids described in the present work for two phylogenetic distant Hatophytes is a contribution to a better understanding on the complex relationship between lipid composition and taxonomy of this important Division of microalgae. Present results can also be useful for a more accurate identification of primary producers in food web studies using fatty acids and intact polar lipids as trophic markers.