Two key problems concern cell membranes during the emergence and early evolution of life: what was their initial composition, and why did the membranes of archaea and bacteria diverge? The composition of the first cell membranes could shed light on the most likely environment for the emergence of life. The opposing stereochemistry of modern lipid glycerol-phosphate headgroups in bacteria and archaea suggests that early membranes were composed of single chain amphiphiles, perhaps both fatty acids and isoprenoids. We investigated the effect of adding isoprenoids to fatty acid membranes using a combination of UV-visible spectroscopy, confocal microscopy and transmission electron microscopy. We tested the stability of these membranes across a pH range and under different concentrations of ionic species relevant to oceanic hydrothermal environments, including Na2+, Cl-, Mg2+, Ca2+, HC O 3 - , Fe3+, Fe2+ and S2-. We also tested the assembly of vesicles in the presence of Fe particles and FeS precipitates. We found that isoprenoids enhance the stability of membranes in the presence of salts but require 30-fold higher concentrations for membrane formation. Intriguingly, isoprenoids strongly inhibit the tendency of vesicles to aggregate together in the presence of either Fe particles or FeS precipitates. These striking physical differences in the stability and aggregation of protocells may have shaped the divergence of bacteria and archaea in early hydrothermal environments.

中文翻译：

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类异戊二烯在生命出现时增强脂肪酸膜的稳定性，可能导致早期脂质分裂。


在生命出现和早期进化过程中，两个关键问题涉及细胞膜：它们的最初组成是什么，以及为什么古细菌和细菌的膜会分开？第一个细胞膜的组成可以揭示最有可能出现生命的环境。细菌和古细菌中现代脂质甘油磷酸头基的相反立体化学表明，早期的膜是由单链两亲物组成的，可能是脂肪酸和类异戊二烯。我们结合紫外-可见光谱、共焦显微镜和透射电子显微镜研究了在脂肪酸膜中添加类异戊二烯的效果。我们测试了这些膜在一定 pH 范围内以及在与海洋热液环境相关的不同离子浓度下的稳定性，包括 Na2+、Cl-、Mg2+、Ca2+、HC O 3 - 、Fe3+、Fe2+ 和 S2-。我们还测试了在 Fe 颗粒和 FeS 沉淀物存在的情况下囊泡的组装。我们发现，类异戊二烯在盐存在的情况下可增强膜的稳定性，但需要高 30 倍的浓度才能形成膜。有趣的是，类异戊二烯在存在 Fe 颗粒或 FeS 沉淀物的情况下强烈抑制囊泡聚集在一起的趋势。原始细胞的稳定性和聚集方面的这些显着的物理差异可能塑造了早期热液环境中细菌和古细菌的分歧。