Thaumarchaeota and Thermoplasmatota are the most abundant planktonic archaea in the sea. Thaumarchaeota contain tetraether lipids as their major membrane lipids, but the lipid composition of uncultured planktonic Thermoplasmatota representatives remains unknown. To address this knowledge gap, we quantified archaeal cells and ether lipids in open ocean depth profiles (0–200 m) of the North Pacific Subtropical Gyre. Planktonic archaeal community structure and ether lipid composition in the water column partitioned into two separate clusters: one above the deep chlorophyll maximum, the other within and below it. In surface waters, Thermoplasmatota densities ranged from 2.11 × 10⁶ to 6.02 × 10⁶ cells/L, while Thaumarchaeota were undetectable. As previously reported for Thaumarchaeota, potential homologs of archaeal tetraether ring synthases were present in planktonic Thermoplasmatota metagenomes. Despite the absence of Thaumarchaeota in surface waters, measurable amounts of intact polar ether lipids were found there. Based on cell abundance estimates, these surface water archaeal ether lipids contributed only 1.21 × 10^–9 ng lipid/Thermoplasmatota cell, about three orders of magnitude less than that reported for Thaumarchaeota cells. While these data indicate that even if some tetraether and diether lipids may be derived from Thermoplasmatota, they would only comprise a small fraction of Thermoplasmatota total biomass. Therefore, while both MGI Thaumarchaeota and MGII/III Thermoplasmatota are potential biological sources of archaeal GDGTs, the Thaumarchaeota appear to be the major contributors of archaeal tetraether lipids in planktonic marine habitats. These results extend and confirm previous reports of planktonic archaeal lipid sources, and further emphasize the need for Thermoplasmatota cultivation, to better characterize the membrane lipid constituents of marine planktonic Thermoplasmatota, and more precisely define the sources and patterns of archaeal tetraether lipid distributions in marine plankton.

Thaumarchaeota 和 Thermoplasmatota 是海洋中最丰富的浮游古菌。Thaumarchaeota 含有四醚脂质作为它们的主要膜脂质，但未培养的浮游热浆体代表的脂质组成仍然未知。为了解决这一知识差距，我们量化了北太平洋亚热带环流的开阔海洋深度剖面（0-200 m）中的古细菌细胞和醚脂质。水柱中的浮游古菌群落结构和醚脂质组成分为两个独立的簇：一个在深层叶绿素最大值上方，另一个在其内部和下方。在地表水中，Thermoplasmatota 的密度范围从 2.11 × 10 ⁶到 6.02 × 10 ⁶细胞/L，而奇古菌是不可检测的。正如之前对奇古菌的报道，古菌四醚环合酶的潜在同源物存在于浮游热浆体宏基因组中。尽管地表水中没有奇古菌，但在那里发现了可测量的完整极性醚脂质。根据细胞丰度估计，这些地表水古细菌醚脂质仅贡献 1.21 × 10 ^–9ng 脂质/嗜热原体细胞，比奇古菌细胞报道的少三个数量级。虽然这些数据表明，即使一些四醚和二醚脂质可能来自 Thermoplasmatota，但它们仅占 Thermoplasmatota 总生物量的一小部分。因此，虽然 MGI Thaumarchaeota 和 MGII/III Thermoplasmatota 都是古菌 GDGT 的潜在生物来源，但 Thaumarchaeota 似乎是浮游海洋栖息地中古菌四醚脂质的主要贡献者。这些结果扩展并证实了先前关于浮游古菌脂质来源的报道，并进一步强调了嗜热菌培养的必要性，以更好地表征海洋浮游嗜热菌的膜脂成分，