Physicochemical Characteristics of Model Membranes Composed of Legionella gormanii Lipids

Abstract

Legionella gormanii is one of the species belonging to the genus Legionella, which causes atypical community-acquired pneumonia. The most important virulence factors that enable the bacteria to colonize the host organism are associated with the cell surface. Lipids building the cell envelope are crucial not only for the membrane integrity of L. gormanii but also by virtue of being a dynamic site of interactions between the pathogen and the metabolites supplied by its host. The utilization of exogenous choline by the Legionella species results in changes in the lipids’ composition, which influences the physicochemical properties of the cell surface. The aim of this study was to characterize the interfacial properties of the phospholipids extracted from L. gormanii cultured with (PL+choline) and without exogenous choline (PL−choline). The Langmuir monolayer technique coupled with the surface potential (SPOT) sensor and the Brewster angle microscope (BAM) made it possible to prepare the lipid monomolecular films (model membranes) and study their properties at the liquid/air interface at 20 °C and 37 °C. The results indicate the effect of the choline addition to the bacterial medium on the properties of the L. gormanii phospholipid membranes. The differences were revealed in the organization of monolayers, their molecular packing and ordering, degree of condensation and changes in the components’ miscibility. These findings are the basis for further research on the mechanisms of adaptation of this pathogen, which by changing the native composition and properties of lipids, bypasses the action of antimicrobial compounds and avoids the host immune attack.

Insight into the Mechanism of Interactions between the LL-37 Peptide and Model Membranes of Legionella gormanii Bacteria

“…In addition, on the C −1 S − π plot, the minimum value more accurately identified the surface pressure at which the monolayer collapsed. The changes in the phospholipid composition caused by the choline presence in the medium for bacteria growth and their influence on the behavior of molecules on the subphase were thoroughly discussed in our previous paper [8]. In summary, the smaller lift-off areas of the π − A isotherms (Figure 4A,B, Table 1) for the PL+choline monolayers suggest that molecules are in closer proximity to each other in comparison to PL−choline.…”

“…The Brewster angle microscope images revealed that the monolayers formed from the lipids isolated from L. gormanii cultured in the medium with exogenous choline were more homogeneous than those formed from the lipids of bacteria cultured without the addition of exogenous choline. The monolayers of lipids extracted from bacteria cultured on the medium without the addition of choline displayed increased flexibility attributed to the presence of shorter chains (C14-C18) of unsaturated fatty acids, as well as a larger content of cardiolipin (21%), leading to the formation of heterogeneities (domains) [8].…”

Susceptibility of Legionella gormanii Membrane-Derived Phospholipids to the Peptide Action of Antimicrobial LL-37—Langmuir Monolayer Studies

“…The analysis of LL-37's influence on single-class monolayers allows one to define which class mainly determines the susceptibility of multi-class model membranes to the peptide. The PE class constitutes 50% of the PL − choline mixture and 38% of PL + choline [9], and the results presented in this paper show that PE at 20 • C is the most susceptible to LL-37 incorporation out of all the analyzed classes. In consequence, it can be assumed that PE's behavior in the presence of the peptide is decisive for the peptide-mixture interactions and defines the 25% and 18% mean molecular area increase registered for PL − choline and PL + choline, respectively [17].…”

“…The peptide embedding observed in our studies is more pronounced for less densely packed PE − choline (Figure 2, Table S1) in comparison to PE + choline. The expansion of the PE − choline monolayers can be associated with a greater content of cyclopropane acid c17:0 [9]. The presence of a cyclopropane ring structure increases the spacing between hydrocarbon chains by reducing their ability to pack tightly due to the weakening of the Lifshitz-van der Waals forces that stabilize chain-chain interactions.…”

“…The PG class was characterized by a high amount of branched-chain fatty acids, namely a15:0 (16%), i16:0 (15%), and a17:0 (6%). Compared to other phospholipids, cardiolipin contained the highest amount of unsaturated acids (16:1∆ 9 , 18:1∆ 9 (where ∆ indicates the location of the unsaturated bond in the acid chain)) and long-chain fatty acids (from 20 to 24 carbon atoms) [9]. The complex composition of bacterial membranes, including their fatty acid profile, significantly impacts sensitivity to antibiotics and antimicrobial peptides.…”