On the bacterial outer membranes: the structure of capsular polysaccharides

Gram-negative bacteria are a diverse group of microorganisms characterized by their unique cell structure. The cell surface of Gram(-) bacteria is decorated by glycans such as lipopolysaccharides (LPS) and capsular polysaccharides (CPS). CPS is a high-molecular-weight biopolymer synthesized on a phosphatidylglycerol lipid anchor inside the bacteria and then pass across the membrane through pores. It is not known whether the lipid anchor is extracted from the inner membrane and integrated into the outer membrane or whether it remains in the inner membrane as the CPS crosses the cell envelope. However, if the lipid part is incorporated into the outer membrane of the Gram(-) bacterium, it causes a reduction in the thickness of the hydrophobic part of the membrane and an increase in flexibility, compared with systems with only the lipid part of the LPS. For these reasons, thanks to NR measurements, exploiting hydrogenated and dehumidified lipids, it would be possible to understand the structure and the position of CPS in the bacterial membrane and therefore to develop more efficient and specific antimicrobial systems.