Abstract
BackgroundMany gram-negative bacteria produce an outer membrane phospholipase A (PldA) that plays an important role in outer membrane function and is associated with virulence.ResultsIn the current study, we characterized a pldA mutant of Coxiella burnetii, an intracellular gram-negative pathogen and the agent of human Q fever. The C. burnetti pldA open reading frame directs synthesis of a protein with conserved PldA active site residues. A C. burnetii ΔpldA deletion mutant had a significant growth defect in THP-1 macrophages, but not axenic medium, that was rescued by complementation. Thin layer chromatography was employed to assess whether pldA plays a role in remodeling membrane lipids during C. burnetii morphological differentiation. Extracted lipids were analyzed from replicating, logarithmic phase large cell variants (LCVs), non-replicating, stationary phase small cell variants (SCVs), and a mixture of LCVs and SCVs. Similar to Escherichia coli, all three forms contained cardiolipin (CL), phosphatidylglycerol (PG) and phosphatidylethanolamine (PE). However, PE and PG were present in lower quantities in the SCV while three additional lipid species were present in higher quantities. Co-migration with standards tentatively identified two of the three SCV-enriched lipids as lyso-phosphatidylethanolamine, a breakdown product of PE, and free fatty acids, which are generally toxic to bacteria. Developmental form lipid modifications required the activity of PldA.ConclusionsCollectively, these results indicate developmentally-regulated lipid synthesis by C. burnetii contributes to colonization of macrophages and may contribute to the environmental stability and the distinct biological properties of the SCV.
Highlights
Many gram-negative bacteria produce an outer membrane phospholipase A (PldA) that plays an important role in outer membrane function and is associated with virulence
We show marked changes in lipid content during differentiation that are attributable to the activity of a predicted outer membrane phospholipase A (PldA)
C. burnetii pldA is required for optimal growth in macrophages CBU0489 is annotated as an outer membrane phospholipase A-encoding gene [11]
Summary
Many gram-negative bacteria produce an outer membrane phospholipase A (PldA) that plays an important role in outer membrane function and is associated with virulence. Replication of the organism proceeds via a bi-phasic developmental cycle, during which it transitions from a large cell variant (LCV) to a Despite the apparent importance of SCVs in C. burnetii disease transmission and pathogenesis, relatively little is known about biochemical changes during transition that confer the unique biological properties of the SCV. The gram-negative cell envelope is composed of an inner and outer membrane, with peptidoglycan separating the two membranes. Both leaflets of the inner membrane are composed of phospholipids, whereas, the outer membrane has an inner leaflet of phospholipids and an outer leaflet of lipopolysaccharide. Phospholipid modifications are common in bacteria and can provide an increase in resistance properties [7]. Cyclopropanation of phospholipid acyl chains in Escherichia coli increases resistance to acid stress [8]
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