Gram-negative bacteria experiencing marine habitats are constantly exposed to stressful conditions dictating their survival and proliferation. In response to these selective pressures, marine microorganisms adapt their membrane system to ensure protection and dynamicity in order to face the highly mutable sea environments. As an integral part of the Gram-negative outer membrane, structural modifications are commonly observed in the lipopolysaccharide (LPS) molecule; these mainly involve its glycolipid portion, i.e., the lipid A, mostly with regard to fatty acid content, to counterbalance the alterations caused by chemical and physical agents. As a consequence, unusual structural chemical features are frequently encountered in the lipid A of marine bacteria. By a combination of data attained from chemical, MALDI-TOF mass spectrometry (MS), and MS/MS analyses, here, we describe the structural characterization of the lipid A isolated from two marine bacteria of the Echinicola genus, i.e., E. pacifica KMM 6172T and E. vietnamensis KMM 6221T. This study showed for both strains a complex blend of mono-phosphorylated tri- and tetra-acylated lipid A species carrying an additional sugar moiety, a D-galacturonic acid, on the glucosamine backbone. The unusual chemical structures are reflected in a molecule that only scantly activates the immune response upon its binding to the LPS innate immunity receptor, the TLR4-MD-2 complex. Strikingly, both LPS potently inhibited the toxic effects of proinflammatory Salmonella LPS on human TLR4/MD-2.
lipid A, lipopolysaccharide (LPS), Marine bacteria, Structural characterization, TLR4 antagonists, Echinicola
NCBI PubMed ID: 34946153Publication DOI: 10.3390/microorganisms9122552Journal NLM ID: 101625893Publisher: Basel, Switzerland: MDPI AG
Correspondence: flaviana.dilorenzo@unina.it
Institutions: Department of Chemical Sciences, University of Naples Federico II, via Cinthia 4, 80126 Naples, Italy, Task Force on Microbiome Studies, University of Naples Federico II, 80126 Naples, Italy, G.B. Elyakov Pacific Institute of Bioorganic Chemistry, Far Eastern Branch, Russian Academy of Sciences, 159/2, Prospect 100 let Vladivostoku, 690022 Vladivostok, Russia, Department of Molecular Medicine and Medical Biotechnologies, University of Naples Federico II, Via S. Pansini n 5, 80131 Naples, Italy, Department of Chemical, Materials and Production Engineering, University of Naples Federico II, Piazzale V. Tecchio 80, 80125 Naples, Italy, Department of Biotechnology and Animal Science, National Ilan University, No. 1, Sec. 1, Shen-Lung Road, Ilan 26099, Taiwan, CEINGE-Biotecnologie Avanzate s.c.ar.l., Via G. Salvatore n 436, 80131 Naples, Italy, Department of Agricultural Sciences, University of Naples Federico II, Via Università 100, 80055 Portici, Italy
Methods: GC-MS, SDS-PAGE, ELISA, acid hydrolysis, MS/MS, MALDI-TOF MS, composition analysis, immunological assays
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