(390g) Assembly of Protocell-like Vesicles in Microscale Hydrothermal Pores Via Synergistic Trapping and Chaotic-Mixing

Identifying and quantifying physical machinery required to drive the assembly of protocell-like vesicles is a continuing unresolved question in the origin of life (OoL). Hydrothermal vents across the universe have gained tremendous interest lately as potential hotspots for these processes owing to the inherently rich biochemical environments and favorable physical conditions. Previous studies have shown the formation of protocell-like vesicles using unlimited fatty acid precursors in regions mimicking thin cracks (d ≤ 100 µm) in the hydrothermal vents resulting in extreme thermal gradients (100-1000 °C/mm) [1-2]. However, these physical conditions do not constitute the predominant volume fraction of pores, while fatty acids are also not representative major cell membrane components. Recent studies have shown thermally actuated chaotic flow, although counterintuitive, are capable of accelerated transport and mixing within these microenvironments [3]. Using a combination of experiments and simulations, we rationally evaluate and quantify optimally favorable 3-D chaotic flow fields with synergistic localized trapping and chaotic-mixing that drive the assembly of micron-sized phosphatidylcholine vesicles, a primary cell membrane component.

Analysis of approximately 10,000 micropores within several cross-sectional cuts of hydrothermal vents using Image J helped determine the physical size ranges of microenvironments representing the major pore volume fraction for experiments. An ensemble of nine model pores were then selected with dimensions and volume within this range and evaluated the growth of small precursor vesicles (0.2 µm) incubated in these environments for 24h under a thermal gradient of 40 °C. Size distribution characterization using Nanoparticle Tracking Analysis (NTA) revealed the classification of the nine data points into three categories of final vesicle size distribution (< 0.6 µm, 0.8-1.0 µm, > 1.0µm). Computational simulations indicate the presence of localized trapping and recirculation via vortexes quantified using Q-criterion and chaotic-mixing with continual refeeding quantified by the Lyapunov exponent and Poincarémaps. These insights are then used to introduce a new 4-D parametric map across a range of thermal gradients (25-55 °C), height (3-20 mm) and aspect ratio (1-8) to associate favorable physical conditions linking the synergistic physically processes identified computationally favoring the growth of micron-sized vesicles identified experimentally thus laying the foundation to pinpoint equivalent conditions within hydrothermal vents. Eventually, we would like to evaluate other factors, both physical and chemical such as vibrational forces and metal ions respectively that could further assist in the formation of protocell-like vesicles.

[1] Budin, et al. (2009) JACS 131, 9628-9629
[2] Mast, et al. (2013) PNAS 110, 8030-8035
[3] Priye, et al. (2017) PNAS 114, 1275-1280