Redox-dependent niche differentiation provides evidence for multiple bacterial sources of glycerol tetraether lipids in lakes.
Redox-dependent niche differentiation provides evidence for multiple bacterial sources of glycerol tetraether lipids in lakes.
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DOI：
10.1073/pnas.1805186115
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发表时间：
2018-10-23
影响因子：
11.1
通讯作者：
Niemann H
中科院分区：
文献类型：
--
作者：
Weber Y;Sinninghe Damsté JS;Zopfi J;De Jonge C;Gilli A;Schubert CJ;Lepori F;Lehmann MF;Niemann H
对未来气候条件的可靠预测需要彻底了解整个地球历史上的气候变异性。微生物分子化石，如细菌跨膜四醚脂[支链甘油二烷基甘油四醚(BrGDGTS)]，已被证明对评估过去的气候条件特别有用，因为它们普遍存在于环境中，并显示出与温度有关的成分变化。然而，产生brGDGT的细菌的身份和生态在很大程度上是未知的，基于brGDGT的古气候重建的机制基础仍然缺乏。在这里，我们提出了对影响湖泊中brGDGT合成的生态参数的见解，表明具有缺氧底水的富营养化湖泊是基于brGDGT重建大陆性气候的首选地点。湖泊沉积物等陆地古气候档案对于我们了解大陆气候系统和模拟未来气候情景至关重要。然而，用于确定古温度的定量代理是稀少的。某些细菌脂类的相对丰度，即支链甘油二烷基甘油四醚(BrGDGTs)，对环境温度的变化做出反应，因此具有巨大的气候重建潜力。然而，由于缺乏对湖泊中产生brGDGT的微生物生态的基础知识，它们在湖泊沉积中的应用受到阻碍。在这里，我们证明了brGDGT是由多组细菌合成的，这些细菌在瑞士一个深湖(卢加诺湖)的氧化还原制度下茁壮成长。这种生态位分配的证据是在好氧和缺氧水团中高度不同的brGDGT清单，以及相应的细菌16S rRNA基因丰度的垂直模式，这意味着沉积的brGDGT记录受到微生物生产者群落组成与温度无关的变化的影响。此外，卢加诺湖和其他34个(周边)阿尔卑斯山湖泊中BrGDGT的稳定碳同位素组成(δ13C)证明，在中营养化到富营养化湖泊系统的氧化还原过渡区，存在着广泛的异养并入。在这种低氧/甲烷营养条件下产生的BrGDGT反映了接近底层的水温，并具有相对较低的δ13C值。根据气候带和水深的不同，以深水/低13C brGDGT为主的湖泊沉积物档案可能比那些BrGDGT来自陆地和/或水生来源且具有明显温度印记的记录更可靠地记录气候变化。
Reliable prediction of future climate conditions requires a thorough understanding of climate variability throughout Earth’s history. Microbial molecular fossils, such as bacterial membrane-spanning tetraether lipids [branched glycerol dialkyl glycerol tetraethers (brGDGTs)], have proven to be particularly useful for the assessment of past climatic conditions, because they occur ubiquitously in the environment and show compositional changes related to temperature. However, the identity and ecology of brGDGT-producing bacteria is largely unknown, and a mechanistic basis for brGDGT-based paleoclimate reconstruction is still lacking. Here, we present insights into the ecological parameters that affect brGDGT synthesis in lakes, demonstrating that eutrophic lakes with oxygen-deprived bottom waters are the preferred sites for brGDGT-based reconstructions of continental climate. Terrestrial paleoclimate archives such as lake sediments are essential for our understanding of the continental climate system and for the modeling of future climate scenarios. However, quantitative proxies for the determination of paleotemperatures are sparse. The relative abundances of certain bacterial lipids, i.e., branched glycerol dialkyl glycerol tetraethers (brGDGTs), respond to changes in environmental temperature, and thus have great potential for climate reconstruction. Their application to lake deposits, however, is hampered by the lack of fundamental knowledge on the ecology of brGDGT-producing microbes in lakes. Here, we show that brGDGTs are synthesized by multiple groups of bacteria thriving under contrasting redox regimes in a deep meromictic Swiss lake (Lake Lugano). This niche partitioning is evidenced by highly distinct brGDGT inventories in oxic vs. anoxic water masses, and corresponding vertical patterns in bacterial 16S rRNA gene abundances, implying that sedimentary brGDGT records are affected by temperature-independent changes in the community composition of their microbial producers. Furthermore, the stable carbon isotope composition (δ13C) of brGDGTs in Lake Lugano and 34 other (peri-)Alpine lakes attests to the widespread heterotrophic incorporation of 13C-depleted, methane-derived biomass at the redox transition zone of mesotrophic to eutrophic lake systems. The brGDGTs produced under such hypoxic/methanotrophic conditions reflect near-bottom water temperatures, and are characterized by comparatively low δ13C values. Depending on climate zone and water depth, lake sediment archives predominated by deeper water/low-13C brGDGTs may provide more reliable records of climate variability than those where brGDGTs derive from terrestrial and/or aquatic sources with distinct temperature imprints.
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5
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