Controls on the hydrogen isotope composition of tetraether lipids in an autotrophic ammonia-oxidizing marine archaeon
Controls on the hydrogen isotope composition of tetraether lipids in an autotrophic ammonia-oxidizing marine archaeon
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DOI：
10.1016/j.gca.2023.04.033
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发表时间：
2023-05
影响因子：
5
通讯作者：
W. Leavitt;S. Kopf;Y. Weber;B. Chiu;J. McFarlin;F. Elling;S. Hoeft-McCann;A. Pearson
中科院分区：
文献类型：
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作者：
W. Leavitt;S. Kopf;Y. Weber;B. Chiu;J. McFarlin;F. Elling;S. Hoeft-McCann;A. Pearson
持久性生物分子的稳定氢同位素组成被用作古水文的代用物。虽然以前的许多工作都集中在植物叶蜡衍生的烷烃上，但原核脂质生物标志物作为H同位素特征载体的潜力仍未得到充分探索，特别是在古细菌中。本文研究了氨氧化化学自养亚硝基藻（nitrosopumilus maritimusstrain SCM1）膜脂中H同位素的分布。在慢速、中速和快速连续培养中提取四醚膜脂，对其裂解的联植烷链进行了氢同位素比率的测量。与最近关于细菌脂肪酸的研究相反，由于中心C和能量代谢，同位素分馏的方向和幅度变化很大（约600‰范围），而本研究中古细菌的联植烷数据相对不变。相对于生长水的加权平均2h /1H分馏值（2εL/W）在-272 ~ -260‰之间，尽管倍增时间（30.8 ~ 92.5 hr）相差3倍，但平均生长速率效应<0.2‰hr−1。这些ε l / w值比文献中大多数异养微生物脂质H同位素测量值更负，与其他自养古菌以及光自养藻类的叶绿醇的测量值相当。随着内环（环戊基+环己基）数量的增加，2ε l / w的海事值也有系统的变化，每增加一个环，海事值增加6.4±2.7‰。利用同位素通量平衡模型，结合对古菌脂质生物合成中H来源的综合分析，我们利用这一观察结果估计了水中H引入的动力学同位素效应（KIEs）；还原辅助因子如黄素和NADPH，以及将电子供体衍生的NADH转化为这些辅助因子的转氢化反应。与以往对细菌和植物的研究结果一致，我们的研究结果表明，古细菌中还原辅因子的KIEs是高度分馏的，而涉及水质子交换的KIEs则不那么分馏。结合对最小生长速率敏感性的观察，我们的结果表明，利用亚硝基藻（又名Thaumarchaeota）的自养3HP/4HB的联phytane可能以几乎恒定的ε l / w值从其生长水体中抵消。与环效应一起，这意味着所有来自共同来源的联苯烷应该有一个可预测的同位素比率顺序，相对于联苯烷环数，允许精确重建环境水的原始δ2H值。总的来说，这些模式表明古细菌联苯烷具有作为古水文代用物的潜力，可以作为叶蜡烷烃的补充或替代。
The stable hydrogen isotope composition of persistent biomolecules is used as a palaeohydrological proxy. While much previous work has focused on plant leaf wax-derivedn-alkanes, the potential of prokaryotic lipid biomarkers as carriers of H isotope signatures remains underexplored, particularly in the Archaea. Here we investigated H isotope distributions in the membrane lipids of the ammonia-oxidizing chemoautotrophNitrosopumilus maritimusstrain SCM1. Hydrogen isotope ratios were measured on the cleaved biphytane chains of tetraether membrane lipids extracted from steady-state continuous cultures cultivated at slow, medium, and fast growth rates. In contrast to recent work on bacterial fatty acids, where the direction and magnitude of isotopic fractionation varies widely (ca.600‰ range) as a function of central C and energy metabolism, archaeal biphytane data in the present work are relatively invariant. The weighted average2H/1H fractionation values relative to growth water (2εL/W) ranged from –272 to –260‰, despite a three-fold difference in doubling times (30.8–92.5 hr), yielding an average growth-rate effect <0.2‰ hr−1. These2εL/Wvalues are more negative than most heterotrophic microbial lipid H isotope measurements in the literature, and are on par with those from other autotrophic archaea, as well as with phytol from photoautotrophic algae.N. maritimusvalues of2εL/Walso varied systematically with the number of internal rings (cyclopentyl + cyclohexyl), increasing for each additional ring by 6.4 ± 2.7‰.Using an isotope flux-balance model in tandem with a comprehensive analysis of the sources of H in archaeal lipid biosynthesis, we use this observation to estimate the kinetic isotope effects (KIEs) of H incorporation from water; from reducing cofactors such as flavins and NADPH, and for the transhydrogenation reaction(s) that convert the electron-donor derived NADH into these cofactors. Consistent with prior studies on bacteria and plants, our results indicate the KIEs of reducing cofactors in archaea are highly fractionating, while those involving exchange of water protons are less so. When combined with the observation of minimal growth-rate sensitivity, our results suggest biphytanes of autotrophic 3HP/4HB utilizing Nitrososphaerota (a.k.a. Thaumarchaeota) may be offset from their growth waters by a nearly constant2εL/Wvalue. Together with the ring effect, this implies that all biphytanes originating from a common source should have a predictable ordering of their isotope ratios with respect to biphytane ring number, allowing precise reconstruction of the original δ2H value of the environmental water. Collectively, these patterns indicate archaeal biphytanes have potential as paleo-hydrological proxies, either as a complement or an alternative to leaf waxn-alkanes.