Alkenoates and alkenones are polyunsaturated long-chain esters and ketones produced by members of the Isochrysidales, an order of haptophyte microalgae. Based on phylogenetic data, members of Isochrysidales have been classified into three groups, with each group showing major differences in preferred growth environments (e.g., salinity). Systematic identification of chemotaxonomic differences among the three groups of Isochrysidales is thus important for paleoenvironmental reconstructions and disentangling mixed alkenone temperature signals. Here, we systematically examined alkenone/alkenoate profiles in culture samples of Group 2 and Group 3 Isochrysidales and environmental sample of Group1 Isochrysidales. Using GC columns with stationary phases of contrasting polarities, we discovered for the first time C₃₇ and C₃₈ ethyl alkenoates (C₃₇OEt and C₃₈OEt) in Group 2 and/or 3 Isochrysidales, extending the longest alkenoate chain length of C₃₆OEt in previous publications. We show that Group 3 Isochrysidales only produce C₃₇OEt, whereas Group 2 Isochrysidales produce both C₃₇OEt and C₃₈OEt alkenoates. Because Group 1 Isochrysidales do not produce alkenoates, C₃₈OEt are specific biomarkers for Group 2 species. The identification of C₃₇OEt and C₃₈OEt in sediments from saline lakes and Chesapeake Bay where sequences of Group 2 DNA have been recovered further validates the use of C₃₈OEt as a Group 2-specific biomarker.

烯酸酯和烯酮是多不饱和长链酯和酮，由等鞭藻目（一种触生植物微藻目）的成员产生。根据系统发育数据，等鞭金藻目的成员被分为三组，每组在偏好的生长环境（例如，盐度）方面表现出主要差异。因此，系统识别三组等鞭金藻属之间的化学分类差异对于古环境重建和解开混合烯酮温度信号非常重要。在这里，我们系统地检查了第 2 组和第 3 组等鞭金藻属的培养样品和第 1 组等鞭金藻属的环境样品中的烯酮/烯酸酯谱。使用具有相反极性固定相的 GC 色谱柱，我们首次发现了 C ₃₇和 C ₃₈乙基链烯酸酯（C ₃₇ OEt 和 C ₃₈ OEt）在第 2 组和/或 3 等鞭金藻目中，延长了之前出版物中 C ₃₆ OEt的最长链烯酸酯链长度。我们表明第 3 组等鞭金藻仅产生 C ₃₇ OEt，而第 2 组等鞭金藻同时产生 C ₃₇ OEt 和 C ₃₈ OEt 链烯酸酯。由于第 1 组等鞭金藻属不产生链烯酸盐，因此 C ₃₈ OEt 是第 2 组物种的特异性生物标志物。在盐湖和切萨皮克湾的沉积物中鉴定了 C ₃₇ OEt 和 C ₃₈ OEt，其中第 2 组 DNA 的序列已经恢复，进一步验证了 C 的使用₃₈ OEt 作为第 2 组特异性生物标志物。