Abstract
Bacteria cells within biofilms are physiologically distinct from their planktonic counterparts. In particular they are more resistant to detrimental environmental conditions. In this study, we monitored the evolution of the phospholipid composition of the inner and outer membranes of P. aeruginosa during the biofilm formation (i.e., from 1-, 2-, to 6-day-old biofilm). Lipidome analyses were performed by electrospray ionization mass spectrometry. In addition to the lipidomic analysis, the fatty acid composition was analysed by gas chromatography/mass spectrometry. We found that the lipidome alterations of the inner and the outer membranes varied with the biofilm age. These alterations in phospholipid compositions reflect a higher diversity in sessile organisms than in planktonic counterparts. The diversity is characterized by the presence of PE 30∶1, PE 31∶0 and PG 31∶0 for the lower masses as well as PE 38∶1, 38∶2, 39∶1, 39∶2 and PG 38∶0, 38∶1, 38∶2, 39∶1, 39∶2 for the higher masses. However, this lipidomic feature tends to disappear with the biofilm age, in particular the high mass phospholipids tend to disappear. The amount of branched chains phospholipids mainly located in the outer membrane decreased with the biofilm age, whereas the proportion of cyclopropylated phospholipids increased in both membranes. In bacteria present in oldest biofilms, i.e., 6-day-old, the phospholipid distribution moved closer to that of planktonic bacteria.
Highlights
Pseudomonas aeruginosa is well known as an opportunistic pathogen that causes a variety of diseases in individuals predisposed to infections as the result of severe burns, wounds, urinary tract or corneal injury, or immunocompromised status [1] and is the leading cause of mortality and morbidity in cystic fibrosis (CF) patients [2]
Bacterial biofilm infections are problematic because sessile bacteria are drastically more resistant to antimicrobials as compared with planktonic counterparts [6,7]
The protective mechanisms involved in biofilms resistance appear to be distinct from those that are responsible for conventional antibiotic resistance and it is becoming evident that biofilm resistance is multifactorial [8]
Summary
Pseudomonas aeruginosa is well known as an opportunistic pathogen that causes a variety of diseases in individuals predisposed to infections as the result of severe burns, wounds, urinary tract or corneal injury, or immunocompromised status [1] and is the leading cause of mortality and morbidity in cystic fibrosis (CF) patients [2]. This bacterium is characterised by its innate resistance to antibiotics due to a low outer membrane (OM) permeability and the presence of active efflux (Mex) systems [3,4]. The biofilm phenotype of P. aeruginosa appears regulated more at the translational and perhaps posttranslational levels than at the transcriptional level, as highlighted by the discrepancies between transcriptomics [10,11] and proteomics [12,13]
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