A tuneable minimal cell membrane reveals that two lipid species suffice for life

Justice, I.; Kiesel, P.; Safronova, N.; von Appen, A.; Sáenz, J. P. (2024) Nature Communications, 15, 9679. DOI: 10.1038/s41467-024-53975-y

Summary

How many lipid species does a cell need to survive? We developed an approach to tune and minimize membrane lipid composition in [[mycoplasma-mycoides|Mycoplasma mycoides]] and its derived minimal cell JCVI-Syn3A, revealing that a two-component lipidome — cholesterol plus a single phospholipid — can support life. Systematic reintroduction of phospholipids with different structural features demonstrated that acyl chain diversity is more important for growth than head group diversity. By tuning lipid chirality with archaeal-type diether lipids, we showed that ancestral lipidomes could have been heterochiral, though heterochirality impaired cellular fitness in these organisms.

Key Findings

• A two-component lipidome (cholesterol + one phospholipid species) can support growth and cell division in both M. mycoides and JCVI-Syn3A — extending the concept of minimal life from the genome to the lipidome.
• By controlling lipid diets through media supplementation, lipidome complexity was reduced from the normal ~20+ species to as few as 2.
• Acyl chain diversity matters more than head group diversity: reintroduction of phospholipids differing in acyl chain structure improved growth more than reintroduction of phospholipids differing in head group identity.
• Introduction of archaeal-type diether phospholipids (opposite chirality to bacterial ester lipids) produced viable heterochiral membranes, but with reduced fitness — addressing the “lipid divide” between Archaea and the rest of life.
• The approach bypasses cellular lipid remodeling by using diether phospholipids that cells cannot enzymatically modify, enabling precise control over membrane composition.

Methods

• Lipid diet tuning: controlled the lipid species provided in growth media for M. mycoides and JCVI-Syn3A, which rely on exogenous lipids due to minimal biosynthetic capacity.
• Diether phospholipids: synthetic archaeal-type lipids resistant to enzymatic remodeling, enabling exact lipidome specification.
• Shotgun lipidomics: quantitative mass spectrometry to verify cellular lipidome composition under each diet.
• Cryo-FIB-SEM: cryo-focused ion beam scanning electron microscopy (with Alexander von Appen, MPI-CBG) to visualize cell morphology.
• Growth assays: phenol red pH-based growth rate measurements across lipid diet conditions.

Significance

This paper established the minimal lipidome — two lipid species — as a new boundary condition for life, complementing the minimal genome defined by the JCVI-Syn3A project. The finding that acyl chain diversity trumps head group diversity for growth provides a key design principle for synthetic membranes. The heterochiral lipid experiments directly probed the evolutionary lipid divide between Archaea and Bacteria/Eukarya, suggesting that the commitment to a single chirality may have been driven by fitness advantages rather than biochemical necessity.