Why archaeal membranes are more permeable than bacterial
Among the earliest branches of the tree of life are two groups of microscopic organisms: Bacteria and Archaea. Initially grouped together as Prokaryotes due to their lack of a defined nucleus, these two groups share some fundamental biochemistry, but differ significantly in several key aspects including cell walls, DNA replication machineries, DNA packing structures, and phospholipid membrane chemistries. This latter distinction, known as the lipid divide, is considered a crucial factor in evolution, highlighting the distinct paths Bacteria and Archaea have taken since diverging from a common ancestor.
It appears that the lipids in archaeal membranes are significantly different from those in bacteria. They are based on isoprenoid chains ether-linked to glycerol-1-phosphate, as opposed to the fatty acid chains ester-linked to glycerol-3-phosphate found in bacteria. However, despite progress in understanding membrane structure, there is still only a partial understanding of how these differences in phospholipid membrane chemistry impact metabolite permeability in biologically relevant contexts.
The study conducted by Stefano Pagliara Group at the University of Exeter has shed light on the differences in membrane permeability between Bacteria and Archaea and revealed that archaeal core lipid membranes are more permeable than bacterial membranes. The authors presented a novel approach for the study of membrane permeability based on microfluidic manipulation of giant unilamellar vesicles composed of archaeal or bacterial type lipids and generated with the Vesicle Prep Pro. Their findings indicate that increased membrane permeability is dependent on both the methyl branches on the lipid tails and the ether bond between the tails and the head group, both of which are present on the archaeal phospholipids. Such differences in permeability must have had profound effects on the cell physiology and proteome evolution of early prokaryotic forms.
Interestingly, in line with increased membrane permeation, Archaea tend to possess a smaller variety of transporter gene families compared to Bacteria. This suggests that Archaea may rely less on specialized transport proteins, thanks to their membranes’ innate ability to allow molecules to pass through more readily. In contrast, Bacteria, with their less permeable membranes, compensate by having a broader array of transporter genes to facilitate the movement of substances across their membranes.
Overall, these results demonstrate that archaeal lipid membranes show selective permeability to compounds beneficial for cellular metabolism, suggesting that early archaeal forms could acquire metabolic resources without diverse transport systems, an advantage that may have influenced early cellular evolution and the development of proto-metabolic networks.
Read the full paper here for more details: https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3002048
Learn more about the Vesicle Prep Pro – an automated device for the preparation of giant unilamellar vesicles (GUVs): https://www.nanion.de/products/vesicle-prep-pro/