LIPIDOMIC ANALYSIS CAN DISTINGUISH BETWEEN TWO MORPHOLOGICALLY SIMILAR STRAINS OF NANNOCHLOROPSIS OCEANICA 1 Shuang Li Key Laboratory of Applied Marine Biotechnology, Ningbo University, Chinese Ministry of Education, Ningbo, Zhejiang 315211, China Ningbo Entry-Exit Inspection and Quarantine Bureau Technology Center of the People’s Republic of China, Ningbo, Zhejiang 315211, China School of Marine Sciences, Ningbo University, Ningbo, Zhejiang 315211, China Jilin Xu 2 Key Laboratory of Applied Marine Biotechnology, Ningbo University, Chinese Ministry of Education, Ningbo, Zhejiang 315211, China Ying Jiang, Chengxu Zhou School of Marine Sciences, Ningbo University, Ningbo, Zhejiang 315211, China Xuejun Yu, Yingying Zhong Ningbo Entry-Exit Inspection and Quarantine Bureau Technology Center of the People’s Republic of China, Ningbo, Zhejiang 315211, China Juanjuan Chen Key Laboratory of Applied Marine Biotechnology, Ningbo University, Chinese Ministry of Education, Ningbo, Zhejiang 315211, China and Xiaojun Yan 2 School of Marine Sciences, Ningbo University, Ningbo, Zhejiang 315211, China The two morphologically similar microalgae NMBluh014 and NMBluh-X belong to two different strains of Nannochloropsis oceanica. They possess obviously different feeding effects on bivalves, but are indistinguishable by 18S rRNA and morphological features. In this work, lipidomic analysis followed by principal component analysis and orthogonal projections to latent structures discriminant analysis provided a clear distinction between these strains. Metabolites that definitively contribute to the classification were selected as potential biomarkers. The most important difference in polar lipids were sulfoquinovosyldiacylglycerol (containing 18:1/16:0 and 18:3/16:0) and monogalactosyldiacylglycerol (containing 18:3/16:3 and 20:5/14:0), which were detected only in NMBluh-X. Additionally, an exhaustive qualitative and quantitative profiling of the neutral lipid triacylglycerol (TAG) in the two strains was carried out. The predominant species of TAG containing 16:1/16:1/16:1 acyl groups was detected only in NMBluh-X with a content of ~93.67  11.85 nmol  mg 1 dry algae at the onset of stationary phase. Meanwhile, TAG containing 16:0/16:0/16:0 was the main TAG in NMBluh014 with a content of 40.25  3.92 nmol  mg 1 . These results provided the most straightforward evidence for differentiating the two species. The metabolomic profiling indicated that NMBluh-X underwent significant chemical and physiological changes during the growth process, whereas NMBluh014 did not show such noticeable time-dependent metabolite change. This study is the first using Ultra Performance Liquid Chromatography coupled with Electrospray ionization- Quadrupole-Time of Flight Mass Spectrometry (UPLC- Q-TOF-MS) for lipidomic profiling with multivariate statistical analysis to explore lipidomic differences of plesiomorphous microalgae. Our results demonstrate that lipidomic profiling is a valid chemotaxonomic tool in the study of microalgal systematics. Key index words: chemotaxonomy; lipidomics; multi- variate data analysis; Nannochloropsis oceanica; UPLC-Q-TOF-MS Abbreviations : BHT, butylated hydroxytoluene; EPA, eicosapentaenoic acids; FA, fatty acid; MS, gas chro- matography-mass spectrometry; OPLS-DA, orthogo- nal projections to latent structures with discriminant 1 Received 2 April 2014. Accepted 24 November 2014. 2 Authors for correspondence: e-mail xujilin@nbu.edu.cn; yanxiao- jun@nbu.edu.cn Editorial Responsibility: M. Posewitz (Associate Editor) J. Phycol. 51, 264–276 (2015) © 2015 Phycological Society of America DOI: 10.1111/jpy.12271 264