Detection of Host-Derived Sphingosine by Pseudomonas aeruginosa Is Important for Survival in the Murine Lung

Abstract

Pseudomonas aeruginosa is a common environmental bacterium that is also a significant opportunistic pathogen, particularly of the human lung. We must understand how P. aeruginosa responds to the lung environment in order to identify the regulatory changes that bacteria use to establish and maintain infections. The P. aeruginosa response to pulmonary surfactant was used as a model to identify transcripts likely induced during lung infection. The most highly induced transcript in pulmonary surfactant, PA5325 (sphA), is regulated by an AraC-family transcription factor, PA5324 (SphR). We found that sphA was specifically induced by sphingosine in an SphR-dependent manner, and also via metabolism of sphingomyelin, ceramide, or sphingoshine-1-phosphate to sphingosine. These sphingolipids not only play a structural role in lipid membranes, but some are also intracellular and intercellular signaling molecules important in normal eukaryotic cell functions as well as orchestrating immune responses. The members of the SphR transcriptome were identified by microarray analyses, and DNA binding assays showed specific interaction of these promoters with SphR, which enabled us to determine the consensus SphR binding site. SphR binding to DNA was modified by sphingosine and we used labeled sphingosine to demonstrate direct binding of sphingosine by SphR. Deletion of sphR resulted in reduced bacterial survival during mouse lung infection. In vitro experiments show that deletion of sphR increases sensitivity to the antimicrobial effects of sphingosine which could, in part, explain the in vivo phenotype. This is the first identification of a sphingosine-responsive transcription factor in bacteria. We predict that SphR transcriptional regulation may be important in response to many sites of infection in eukaryotes and the presence of homologous transcription factors in other pathogens suggests that sphingosine detection is not limited to P. aeruginosa.

Evidence and role for bacterial mucin degradation in cystic fibrosis airway disease

“…In this context, fermentative anaerobes aspirated from the oral cavity that become established in the lower airways may play a central role in the progression of CF lung disease. Expectorated sputum and many of its specific constituents-lipids [15,17], amino acids [16], and modified sugars [40], for example-are known to support bacterial growth in vitro and have been studied in detail. Yet, how the majority of these compounds are made available within the CF airways has not been defined.…”

“…The respiratory tract contains a number of host compounds that can be used by microbes as nutrient sources, including immunoglobulins, cytokines, defensins and lactoferrin [8,9], yet these are unlikely to be present at concentrations to support the dense microbiota of the CF airways [10][11][12][13]. Additionally, studies of CF sputum from adult patients have shown an abundance of small molecules that can support the growth of pathogens in vitro, including sugars, fatty acids, phospholipids, and amino acids [14][15][16][17]. However, the mechanism by which these compounds reach high abundance in airway mucus remains poorly defined.…”

Ceramide and sphingosine in pulmonary infections

“…Thus, ceramide acts by re-organizing molecules in cells and can control many receptor-mediated and non-receptor-mediated cellular activation processes by changing the biophysics of the membrane. In accordance, ceramide-enriched membrane platforms have been shown to be formed in cells after the application of a variety of stimuli, including CD95 , CD40 (Grassmé et al, 2002), DR5 (Dumitru and Gulbins, 2006), FcγRII (Abdel Shakor et al, 2004), and the PAF-receptor (Göggel et al, 2004); infection with P. aeruginosa (Grassmé et al, 2003a), Neisseriae gonorrhoeae (Grassmé et al, 1997), Neisseria meningitides (Simonis et al, 2014), rhinovirus (Grassmé et al, 2005), or measles virus (Gassert et al, 2009;Avota et al, 2011); or stress stimuli such as UV-light (Charruyer et al, 2005), gamma-irradiation (Rotolo et al, 2005), or treatment with cisplatin (Lacour et al, 2004) or Cu 2+ (Lang et al, 2007).…”

Neutrophils Kill Reactive Oxygen Species-Resistant Pseudomonas aeruginosa by Sphingosine

“…At least P. aeruginosa PAO-1 expresses sphingosine response elements, i.e. sphA, which are specifically induced by sphingosine via a sphingosine-specific transcription factor (PA5324), a member of the AraC-family transcription factor, named SphR [39]. Deletion of the SphR transcription factor resulted in reduced bacterial survival during mouse lung infection and increased sensitivity of the pathogen to the antimicrobial effects of sphingosine.…”