Photo credit: www.sciencedaily.com

New Insights into the Origins of Life: Polyester Microdroplets as Protocells

A prominent hypothesis suggests that life’s beginnings on Earth stem from the gradual evolution of simple chemical molecules into more complex structures, eventually leading to the formation of protocells—primitive, non-living entities that served as forerunners to contemporary cells. Research has recently highlighted polyester microdroplets as compelling candidates for these early protocells. These microdroplets result from the polymerization of alpha-hydroxy acids (αHAs), substances that are thought to have been present on the primordial Earth, possibly generated by lightning strikes or brought in via meteorites, followed by basic rehydration in aqueous environments. A new study conducted by scientists at the Earth-Life Science Institute (ELSI) in Tokyo offers fresh evidence supporting the creation of polyester microdroplets under a broader spectrum of plausible prebiotic conditions than previously assumed.

This research was spearheaded by Mahendran Sithamparam, a PhD candidate from the Space Science Center (ANGKASA) at the National University of Malaysia. Co-supervised by Associate Professor Tony Z. Jia of ELSI and Research Scientist Kuhan Chandru from ANGKASA, the team focused on the processes that enable these microdroplets to form in conditions that more accurately mirror those of early Earth. Their findings revealed that polyester microdroplets could indeed form in environments containing significant salt levels, at low concentrations of αHA, and in minimal reaction volumes. This approach marks an important departure from earlier studies that primarily examined droplet formation under high concentrations or in larger bodies of water, such as lakes or thermal springs. The results suggest that polyester protocells were likely more ubiquitous than previously recognized, potentially arising in limited spaces like rock pores or in saline environments such as briny pools or deep sea settings.

Past research from the team demonstrated that polyester microdroplets could be synthesized through a simple dehydration technique. Heating phenyllactic acid (PA), a variant of αHA, to 80°C transformed it into a gel-like material that subsequently formed membraneless droplets upon rehydration. The current study aimed to determine if these microdroplets could form under more dilute conditions akin to those expected in prebiotic Earth scenarios. “Previous lab tests typically employed high concentrations and substantial volumes of αHAs, which may not have been representative of early Earth conditions,” Jia remarks. “Our objective was to explore whether the assembly of protocells would have been feasible under realistic circumstances.”

To better simulate these conditions, the researchers scaled back the concentration and volume of PA during their experiments. They found that polyester synthesis and droplet formation could occur using as little as 500 µL of 1 mM PA or just 5 µL of 500 mM PA. Such findings imply that polyester microdroplets could have spontaneously appeared in both confined spaces like rock pores or in dilute environments, such as those following significant flooding or rainfall.

To further investigate, the research team performed experiments to mimic salinity levels characteristic of ancient oceans. By introducing 1M concentrations of NaCl, KCl, and MgCl2 to the PA reactants, they discovered that polyester synthesis and microdroplet formation could successfully take place in the presence of NaCl and KCl, but not in MgCl2. This indicates that the formation of polyester microdroplets may have been more probable in bodies of water with specific salt compositions, particularly those rich in NaCl and KCl yet lower in MgCl2, conditions favorable for αHA polymerization and subsequent droplet assembly. “Our results strongly suggest that polyester protocells were likely more prevalent on early Earth than we previously thought, guiding future laboratory explorations into this area,” notes Chandru. “A varied range of environments—spanning oceanic, freshwater, hypersaline, and restricted habitats like rock pores—could have supported the genesis of these early protocells, potentially on Earth and elsewhere in the universe.”

This research owes its success to the ELSI Visitor Program, which encourages international collaboration among ELSI researchers. The program facilitated Sithamparam’s two visits to ELSI in 2023 and also supported graduate student Ming-Jing He’s experimental work during the summer of 2023 for her master’s thesis. All experiments conducted during this study took place at ELSI, with the results published in the ACS Bio & Med Chem Au Special Issue, 2024 Rising Stars in Biological, Medicinal, and Pharmaceutical Chemistry, in which Jia is recognized as an awardee.

Source
www.sciencedaily.com