Growth of Staphylococcus aureus in the presence of oleic acid shifts the glycolipid fatty acid profile and increases resistance to antimicrobial peptides.

Staphylococcus aureus readily adapts to various environments and quickly develops antibiotic resistance, which has led to an increase in multidrug-resistant infections. Hence, S. aureus presents a significant global health issue and its adaptations to the host environment are crucial for understanding pathogenesis and antibiotic susceptibility. When S. aureus is grown conventionally, its membrane lipids contain a mix of branched-chain and straight-chain saturated fatty acids. However, when unsaturated fatty acids are present in the growth medium, they become a major part of the total fatty acid composition. This study explores the biophysical effects of incorporating straight-chain unsaturated fatty acids into S. aureus membrane lipids. Membrane preparations from cultures supplemented with oleic acid showed more complex differential scanning calorimetry scans than those grown in tryptic soy broth alone. When grown in the presence of oleic acid, the cultures exhibited a transition significantly above the growth temperature, attributed to the presence of glycolipids with long-chain fatty acids causing acyl chain packing frustration within the bilayer. Functional aspects of the membrane were assessed by studying the kinetics of dye release from unilamellar vesicles induced by the antimicrobial peptide mastoparan X. Dye release was slower from liposomes prepared from cells grown in oleic acid-supplemented cultures, suggesting that changes in membrane lipid composition and biophysics protect the cell membrane against peptide-induced lysis. These findings underscore the intricate relationship between the growth environment, membrane lipid composition, and the physical properties of the bacterial membrane, which should be considered when developing new strategies against S. aureus infections.

Microbial dynamics in biogas digesters treating lipid-rich substrates via genome-centric metagenomics.

Co-digestion with lipid-rich substrates is a likely strategy in biogas plants, due to their high energy content. However, the process stability is vulnerable to inhibition due to the sudden increase of fatty-acid concentration. Therefore, techniques that promote the adaptation of the microorganisms to the presence of lipids have been proposed. In this frame, the initial hypothesis of the work was that a gradual change in feedstock composition would enable us to elucidate the microbial organisation as a result of deterministic (i.e. chemical composition of influent) and stochastic (e.g. interspecies interactions) factors. This study investigates the response of the biogas microbiome to gradual increment of the Organic Loading Rate by supplementing the influent feedstock with Na-Oleate. The results showed that as a response to the feedstock shifts three clusters describing microbes behaviours were formed. The dynamics and the functional role of the formed microbial clusters were unveiled, providing explanations for their abundance and behavior. Process monitoring indicated that the reactors responded immediately to lipid supplementation and they managed to stabilize their performance in a short period of time. The dominance of Candidatus Methanoculleus thermohydrogenotrophicum in the biogas reactors fed exclusively with cattle manure indicated that the predominant methanogenic pathway was hydrogenotrophic. Additionally, the abundance of this methanogen was further enhanced upon lipid supplementation and its growth was supported by syntrophic bacteria capable to metabolize fatty acids. However, with the shift back to the original feedstock (i.e. solely cattle manure), the microbial dynamicity significantly altered with a remarkable increment in the abundance of a propionate degrader affiliated to the order of Bacteroidales, which became the predominant microorganism of the consortium.

Measurement of Cell Membrane Fluidity by Laurdan GP: Fluorescence Spectroscopy and Microscopy.

Membrane fluidity is a critical parameter of cellular membranes which cells continuously strive to maintain within a viable range. An interference with the correct membrane fluidity state can strongly inhibit cell function. Triggered changes in membrane fluidity have been postulated to contribute to the mechanism of action of membrane targeting antimicrobials, but the corresponding analyses have been hampered by the absence of readily available analytical tools. Here, we provide detailed protocols that allow straightforward measurement of antibiotic compound-triggered changes in membrane fluidity both in vivo and in vitro.

Lipid Adaptation of Shrimp Rimicaris exoculata in Hydrothermal Vent.

The shrimp Rimicaris exoculata is the most abundant species in hydrothermal vents. Lipids, the component of membranes, play an important role in maintaining their function normally in such extreme environments. In order to understand the lipid adaptation of R. exoculata (HV shrimp) to hydrothermal vents, we compared its lipid profile with the coastal shrimp Litopenaeus vannamei (EZ shrimp) which lives in the euphotic zone, using ultra performance liquid chromatography electrospray ionization-quadrupole time-of-flight mass spectrometry. As a result, the following lipid adaptation can be observed. (1) The proportion of 16:1 and 18:1, and non-methylene interrupted fatty acid (48.9 and 6.2 %) in HV shrimp was higher than that in EZ shrimp (12.7 and 0 %). While highly-unsaturated fatty acids were only present in the EZ shrimp. (2) Ceramide and sphingomyelin in the HV shrimp were enriched in d14:1 long chain base (96.5 and 100 %) and unsaturated fatty acids (67.1 and 57.7 %). While in the EZ shrimp, ceramide and sphingomyelin had the tendency to contain d16:1 long chain base (68.7 and 75 %) and saturated fatty acids (100 and 100 %). (3) Triacylglycerol content (1.998 ± 0.005 nmol/mg) in the HV shrimp was higher than that in the EZ shrimp (0.092 ± 0.005 nmol/mg). (4) Phosphatidylinositol and diacylglycerol containing highly-unsaturated fatty acids were absent from the HV shrimp. (5) Lysophosphatidylcholine and lysophosphatidylethanolamine were rarely detected in the HV shrimp. A possible reason for such differences was the result of food resources and inhabiting environments. Therefore, these lipid classes mentioned above may be the biomarkers to compare the organisms from different environments, which will be benefit for the further exploitation of the hydrothermal environment.