A food chain of ribozymes built on an ancestral strand
Molecular life forms in the prebiotic earth were capable of self-reproduction from basic building blocks. However, scarcity of building blocks likely led to the evolution of heterotrophic, predatory species. In this work we reconstruct a simple model of such interactions between RNA molecules, based on RNA strands found in sinkhole mineral pools in the Dead Sea. These RNA strands exhibited significant stability in this divergent chemical environment, and contained sequence motifs reminiscent of two ribozyme species, suggesting they could be ancestral to both. We built a system in which a single ancestral RNA strand serves as a limiting resource forming two different species of ribozymes that compete over it. One of these species is capable of metabolizing the other in order to free more of this resource, driving the assembly of additional copies of itself. This interaction resembles a rudimentary food chain, the dynamics of which is sensitive to environmental factors such as temperature and magnesium concentrations, with competitive advantage shifting between the species. Taken together, these findings highlight a hypothetical feature of prebiotic life, and hint at the possibility that heterotrophic RNA is a phenomenon that might still occur today in some unique geochemical niches, and even in the overlooked background of modern biological systems.