The emergence of competition between model protocells

Abstract

The transition from independent molecular entities to cellular structures with integrated behaviors was a crucial aspect of the origin of life. We show that simple physical principles can mediate a coordinated interaction between genome and compartment boundary, independent of any genomic functions beyond self-replication. RNA, encapsulated in fatty acid vesicles, exerts an osmotic pressure on the vesicle membrane that drives the uptake of additional membrane components, leading to membrane growth at the expense of relaxed vesicles, which shrink. Thus, more efficient RNA replication could cause faster cell growth, leading to the emergence of Darwinian evolution at the cellular level.

Fig. 1

Stopped-flow mixing of isotonic and swollen oleate vesicles (1:1 molar ratio) in 0.2 M bicine, pH 8.5. Relative surface area was measured by the FRET assay; membrane growth decreases probe density, causing the FRET signal to decrease. Isotonic vesicles, labeled with FRET dyes, were mixed with unlabeled isotonic (A) or swollen (B) vesicles. The solid line indicates a single exponential decay curve fit with rate constant k = 0.09 s⁻¹. Swollen vesicles, labeled with FRET dyes, were mixed with unlabeled swollen (C) or isotonic (D) vesicles. The solid line indicates the single exponential curve fit (k = 0.08 s⁻¹). Isotonic (E) or swollen (F) POPC vesicles, labeled with FRET dyes, were mixed with unlabeled isotonic (open circles) or swollen (solid circles) POPC vesicles.

Fig. 2

(A) Change in surface area of isotonic vesicles mixed with different ratios of swollen vesicles, measured by FRET assay. Error bars indicate 95% confidence intervals for at least three trials. Time scale of intervesicular exchange of R18 in oleate (B) or MA:GMM (C) vesicles, measured by fluorescence dequenching. (B) Solid line indicates the single exponential curve fit (k = 3.1 min⁻¹). (C) Solid line indicates a single exponential curve fit (k = 0.06 min⁻¹).

Fig. 3

Intervesicle competition using tRNA to swell MA:GMM vesicles. Isotonic (A) or swollen (B) vesicles were labeled with FRET dyes and mixed with unlabeled swollen vesicles pressurized by tRNA (open circles), isotonic vesicles (solid circles), or buffer only (triangles). (A) Solid line indicates a single exponential curve fit (k = 0.09 min⁻¹). (B) Solid line indicates a single exponential curve fit (k = 0.1 min⁻¹).