Rapid growth and fusion of protocells in surface-adhered membrane networks

Abstract

Elevated temperatures might have promoted the nucleation, growth and replication of protocells on the early Earth. Recent reports have shown evidence that moderately high temperatures not only permit protocell assembly at the origin of life, but could have actively supported it. Here we show the fast nucleation and growth of vesicular compartments from autonomously formed lipid networks on solid surfaces, induced by a moderate increase in temperature. Branches of the networks, initially consisting of self-assembled interconnected nanotubes, rapidly swell into microcompartments which can spontaneously encapsulate RNA fragments. The increase in temperature further causes fusion of adjacent networkconnected compartments, resulting in the redistribution of the RNA. The experimental observations and the mathematical model indicate that the presence of nanotubular interconnections between protocells facilitates the fusion process.The important role of solid surface support for the autonomous formation of primitive protocells has been suggested earlier in the context of the origin of life 1,2 . Hanczyc, Szostak et al. showed that vesicle formation from fatty acids was significantly enhanced in the presence of solid particle surfaces consisting of natural minerals or synthetic materials 1,2 . Particularly the silicate-based minerals accelerated the vesicle generation.In a recent report, we showed the autonomous formation and growth of surface adhered protocell populations as a result of a sequence of topological transformations on a solid substrate 3 . Briefly, upon contact with a mineral-like solid substrate, a lipid reservoir spreads as a double bilayer membrane. The distal membrane (upper -with respect to the surface-) ruptures and forms a carpet of lipid nanotubes. Over the course of a few hours, fragments of these nanotubes swell into giant, strictly unilamellar vesicular compartments. This relatively slow process is entirely self-driven and only requires a lipid reservoir as source, a solid surface, and surrounding aqueous media. The resulting structure consists of thousands of lipid compartments, which are physically connected to each other via a

Did Solid Surfaces Enable the Origin of Life?

“…The protocell networks can be formed from membranes consisting of phospholipids only, or from mixtures of phospholipids and fatty acids [ 35 ]. The networks have been shown to encapsulate water soluble compounds, even RNA and DNA [ 35 , 36 , 37 ]. Especially RNA has been a molecule of interest in origin of life studies, as it can act uniquely both as a genetic information carrier and an enzyme analog, catalyzing its own replication [ 38 ].…”

“…The ability of model protocells to encapsulate and maintain RNA has therefore been widely investigated. The surface-adhered compartments can grow rapidly and fuse with merging of contents [ 36 ], passively replicate by transporting material through the nanotubes [ 39 ], divide, migrate, and re-attach to a surface in remote locations [ 33 ]. The protocell networks can also grow in groups in a colony-like manner, where the membranes of the individual compartments are in physical contact with each other [ 35 , 37 ].…”

“…Another type of biomembrane morphology occurring as a result of surface interactions is the interconnected micro-container network [ 35 , 36 ] ( Figure 3 and Figure 4 B). The containers in such physical network may have accommodated different prebiotic chemical reaction networks [ 44 ].…”

Subcompartmentalization and pseudo-division of model protocells

“…2m, inset) where some of them coalesce upon physical contact. A recent study has reported on the merging of lipid vesicles if they are in close proximity in a locally heated zone 46 . Note that in order to elevate the temperature locally under avoidance of strong convection, we used an optical fiber and IR-B radiation (1470 nm, cf.…”

“…An optical fiber coupled to an IR-B laser (cf. S3) was assembled to locally increase the temperature in the sample 46,59 . A semiconductor diode laser (HHF-1470-6-95, λ = 1470 nm , Seminex), driven with an 8 A power source (4308 Laser Source, Arroyo Instruments) was used in combination with an 0.22 NA multimode optical fiber with 50 µm core diameter (Ocean Optics).…”