Arsenolipids in the green alga Coccomyxa (Trebouxiophyceae, Chlorophyta)

Abstract

Lipid-like compounds containing a dimethylarsinoyl group, i.e. Me₂As(O)-, have been identified by liquid chromatography/inductively coupled plasma mass spectrometry (LC/ICP-MS) and non-aqueous reversed-phase high-performance liquid chromatography (positive and/or negative high-resolution tandem electrospray ionization mass spectrometry (NARP-HPLC/HR-ESI^+(-)-MS/MS) from three strains of green algae of the genus Coccomyxa (Trebouxiophyceae, Chlorophyta). The algae were cultivated in a medium containing 10 g arsenic/L, i.e. 133.5 mmol/L of Na₂HAsO₄.7H₂O. After extraction by methyl-tert-butyl ether (MTBE), total lipids were analyzed by ICP-MS or ESI-MS without any further separation or fractionation. A total of 39 molecular species of arsenic triacylglycerols (AsTAG), 15 arsenic phosphatidylcholines (AsPC), 8 arsenic phosphatidylethanolamines (AsPE), 6 arsenic phosphatidylinositols (AsPI), 2 arsenic phosphatidylglycerols (AsPG) and 5 unknown lipids (probably ceramides) were identified. The structures of all molecular species were confirmed by tandem MS. Dry matter of the individual strains contained different amounts of total arsenolipids, i.e. C. elongata CCALA 427 (0.32 mg/g), C. onubensis (1.48 mg/g), C. elongata S3 (2.13 mg/g). On the other hand, there were only slight differences between strains in the relative abundances of individual molecular species. Possible biosynthesis of long-chain lipids with the end group Me₂As(O) has also been suggested.

Keywords: Arsenolipids; Coccomyxa elongata; Coccomyxa onubensis; Dimethylarsinoyl long chains; Green alga; Inductively coupled plasma mass spectrometry (ICP-MS); Non-aqueous reversed-phase high-performance liquid chromatography (NARP-HPLC); Positive/negative high-resolution tandem electrospray ionization mass spectrometry (HR-ESI-MS/MS); Trebouxiophyceae.