Structure characterization of phospholipids and lipid A of Pseudomonas putida KT2442

Molecular Mechanisms of Pathogenic Fungal Virulence Regulation by Cell Membrane Phospholipids

Pathogenic fungi represent a growing concern for human health, necessitating a deeper understanding of their molecular mechanisms of virulence to formulate effective antifungal strategies. Recent research has increasingly highlighted the role of phospholipid components in fungal cell membranes, which are not only vital for maintaining cellular integrity but also significantly influence fungal pathogenicity. This review focuses on the impact of membrane phospholipid composition on fungal growth, morphogenesis, stress responses, and interactions with host cells. To be specific, membrane phospholipid composition critically influences fungal virulence by modulating growth dynamics and morphogenesis, such as the transition from yeast to hyphal forms, which enhances tissue invasion. Additionally, phospholipids mediate stress adaptation, enabling fungi to withstand host-derived oxidative and osmotic stresses, crucial for survival within hostile host environments. Phospholipid asymmetry also impacts interactions with host cells, including adhesion, phagocytosis evasion, and the secretion of virulence factors like hydrolytic enzymes. These adaptations collectively enhance fungal pathogenicity by promoting colonization, immune evasion, and damage to host tissues, directly linking membrane architecture to infection outcomes. By elucidating the molecular mechanisms involved, we aim to underscore the potential of targeting phospholipid metabolic pathways as a promising avenue for antifungal therapy. A comprehensive understanding of how membrane phospholipid composition regulates the virulence of pathogenic fungi can provide valuable insights for developing novel antifungal strategies.

Investigating lipid headgroup composition within epithelial membranes: a systematic review

Membrane lipid composition is often quoted within the literature, but with very little insight into how or why these compositions vary when compared to other biological membranes. One prominent area that lacks understanding in terms of rationale for lipid variability is the human gastro-intestinal tract (GIT). We have carried out a comprehensive systematic literature search to ascertain the key lipid components of epithelial membranes, with a particular focus on addressing the human GIT and to use compositional data to understand structural aspects of biological membranes. Both bacterial outer membranes and the human erythrocyte membrane were used as a comparison for the mammalian [epithelial] membranes and to understand variations in lipid presence. We show that phosphatidylcholine (PC) lipid types tend to dominate (33%) with phosphatidylethanolamines (PE) and cholesterol having very similar abundances (25 and 23% respectively). This systematic review presents a detailed insight into lipid headgroup composition and roles in various membrane types, with a summary of the distinction between the major lipid bilayer forming lipids and how peripheral lipids regulate charge and fluidity. The variety of lipids present in biological membranes is discussed and rationalised in terms function as well as cellular position.

Identification and structural characterization of lipid A from Escherichia coli, Pseudomonas putida and Pseudomonas taiwanensis using liquid chromatography coupled to high-resolution tandem mass spectrometry

RATIONALE

Lipid A is a part of the lipopolysaccharide layer, which is a main component of the outer membrane from Gram-negative bacteria. It can be sensed by mammalians to identify the presence of Gram-negative bacteria in their tissues and plays a key role in the pathogenesis of bacterial infections. Lipid A is also used as an adjuvant in human vaccines, emphasizing the importance of its structural analysis.

METHODS

In order to distinguish and characterize various lipid A species, a liquid chromatography coupled to tandem mass spectrometry (LC/MS/MS) method was developed. Isolation of lipid A from different bacteria was carried out using a modified Bligh and Dyer extraction following a mild acid hydrolysis. Chromatography was performed using a bifunctional reversed-phase-based stationary phase. High-resolution MS using negative electrospray ionization was applied and MS/MS experiments utilizing high-energy collisional dissociation generated diagnostic product ions, which allowed the assignment of the side chains to distinct positions of the lipid A backbone.

RESULTS

The method was applied to lipid A isolations of Escherichia coli (E. coli), Pseudomonas putida (P. putida) and Pseudomonas taiwanensis (P. taiwanensis). Various lipid A species were identified by their accurate masses and their structures were characterized using MS/MS experiments. Previously described lipid A structures from E. coli were identified and their structures confirmed by MS/MS. For the biotechnologically relevant strains P. putida and P. taiwanensis, we confirmed species by MS/MS, which have previously only been analyzed using MS. In addition, several lipid A species were discovered that have not been previously described in the literature.

CONCLUSIONS

The combination of LC and MS/MS enabled the selective and sensitive identification and structural characterization of various lipid A species from Gram-negative bacteria. These species varied in their substituted side chains, speaking of fatty acids and phosphate groups. Characteristic product ions facilitated the assignment of side chains to distinct positions of the lipid A backbone.

Partial structure and immunological properties of lipopolysaccharide from marine-derived Pseudomonas stutzeri KMM 226

The partial structure and immunology of the lipopolysaccharide (LPS) of Pseudomonas stutzeri KMM 226, a bacterium isolated from a seawater sample collected at a depth of 2000 m, was characterised. The O-polysaccharide was built up of disaccharide repeating units constituted by L-Rhap and D-GlcpNAc: →2)-α-L-Rhap-(1→3)-α-D-GlcpNAc-(1→. The structural analysis of the lipid A showed a mixture of different species. The major species were hexa-acylated and penta-acylated lipids A, bearing the 12:0(3-OH) in amide linkage and 10:0(3-OH) in ester linkage, while the secondary fatty acids were present only as 12:0. The presence of 12:0(2-OH) was not detected. The immunology experiments demonstrated that P. stutzeri KMM 226 LPS displayed a low ability to induce TNF-α, IL-1β, IL-6, IL-8 and IL-10 cytokine production and acted as an antagonist of hexa-acylated Escherichia coli LPS in human blood in vitro.