(412e) Assembly of Protocell-like Vesicles Via Chaotic Convective Flow in Micro-Scale Hydrothermal Pores

An
important open question in the origin of life involves identifying physical processes
capable of driving assembly of lipid precursors into primitive cell membranes
under prebiotic conditions. Thermal diffusion has recently been proposed as a
potential enrichment mechanism based on experiments demonstrating fatty acid
aggregation and vesicle formation in capillaries (0.1 ~ 0.01 mm diameter) [1-3]. But this process requires thermal gradients
much steeper than those likely to have existed in naturally occurring
hydrothermal networks. Here we show how microfluidic chaotic thermal convection
[4] offers an alternative mechanism that
effectively promotes self-assembly of vesicular bodies under realistic
hydrothermal pore conditions (1 ~ 10 mm diameter; Fig. 1). Experimental
characterization of vesicles formed by oleic acid (critical aggregate
concentration (cac) 80 μM)
and 06:0 phosphatidylcholine (cac 15mM) using optical
microscopy, dynamic light scattering, and nanoparticle tracking analysis
reveals formation of a statistically significant population of micron-sized
vesicles upon incubation under chaotic convective flows. Data from these
experiments are used to validate a computational model that allows us to
rationally select flow states where local enrichment above the cac can be achieved, overcoming thermodynamic barriers that
would ordinarily favor hydrolytic decomposition over formation of protocell-like vesicles. We also explore
the ability of metal cations present in the early ocean to act as fusing agents
that further promote formation and stabilization of micron-sized vesicles [5, 6]. The results of these studies suggest that
microliter-scale chaotic thermal convection offers an intriguing mechanism to
achieve local enrichment above the cac, potentially
explaining how membrane encapsulated protocells could emerge from dilutely dispersed precursors under prebiotic conditions.

References

[1] D. E. Epps, E. Sherwood, J. Eichberg and
J. Or. “Cyanamide mediated syntheses under
plausible primitive Earth conditions V. The synthesis of phosphatidic acids.” J. Mol.
Evol 11 (1978): 279-292.

[2] M. Rao, J. Eichberg and J. Oró. “Synthesis of phosphatidylcholine under
possible primitive Earth conditions.” Journal of Molecular Evolution 18 (1982): 196-202.

[3] I. Budin, R. J. Bruckner and J. W.
Szostak. “Formation of protocell-like
vesicles in a thermal diffusion column.”
Journal of the American Chemical
Society 131 (2009): 9628-9629.

[4] A. Priye, Y. Yu, Y. A. Hassan and V. M.
Ugaz. “Synchronized chaotic targeting
and acceleration of surface chemistry in prebiotic hydrothermal
microenvironments.” Proceedings of the National Academy of Sciences of the United States of
America 114 (2017): 1275-1280.

[5] S. Mondal Roy and M. Sarkar. “Membrane fusion induced by small molecules
and ions.” J Lipids 2011 (2011): 528784.

[6] V. S. Markin, M. M. Kozlov and V. L.
Borovjagin. “On the theory of membrane
fusion. The stalk mechanism.” Gen Physiol Biophys 3 (1984): 361-377.

Figure 1. Convectively
driven chemical enrichmentcan be exploited to locally increase lipid
concentrations above the critical aggregate concentration (cac), enabling
assembly of vesicular protocells.