Data_Sheet_1_Planktonic Archaeal Ether Lipid Origins in Surface Waters of the North Pacific Subtropical Gyre.docx

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.

浮游古菌类和热液古菌类是海洋中最为丰富的浮游古菌。浮游古菌类以其四醚脂质作为主要膜脂质，然而，未培养的浮游热液古菌类的脂质组成仍属未知。为填补这一知识空白，本研究在北太平洋副热带环流区的开阔海域深度剖面（0-200米）中量化了古菌细胞和醚脂。浮游古菌群落结构及其水柱中的醚脂组成可分为两个独立的簇：一个位于深层叶绿素最大值之上，另一个位于其中及以下。在表层水体中，热液古菌的密度介于2.11 × 10^6至6.02 × 10^6个细胞/升之间，而浮游古菌则无法检测到。正如之前对浮游古菌的报道，古菌四醚环合酶的同源物存在于浮游热液古菌的宏基因组中。尽管表层水体中缺乏浮游古菌，但仍然发现了可测量的完整极性醚脂。基于细胞丰度估计，这些表层水体中的古菌醚脂仅占1.21 × 10^-9 ng脂质/热液古菌细胞，约为浮游古菌细胞的三个数量级。尽管这些数据表明，即使部分四醚和二醚脂质可能来源于热液古菌，它们也仅占热液古菌总生物量的微小部分。因此，尽管MGI浮游古菌和MGII/III热液古菌都是古菌GDGTs的生物来源，但浮游古菌似乎仍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，并进一步强调了培养热液古菌的重要性，以更好地表征海洋浮游热液古菌的膜脂成分，并更精确地定义古菌四醚脂质在海洋浮游生物中的来源和分布模式。