Characterization of membrane lipidome changes in Pseudomonas aeruginosa during biofilm growth on glass wool

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.

Figure 1. Formation of P. aeruginosa biofilms on glass wool after 24 h as observed by scanning electron microscopy.

For complementary information on P. aeruginosa biofilms grown on glass wool, see .

Figure 2. Evolution of the proportions of the main phosphatidyletnolamines and phosphatidylglycerols in P. aeruginosa inner and outer membranes.

The proportions obtained for planktonic bacteria is represented in dashed lines. Error bars are given with a 95% confidence interval. Results of ANOVA test for the phospholipid proportions in sessile bacteria are shown (***, p-value<0,001; **, p-value<0,01; *, p-value<0,1 none p-value>0,1 (not statically relevant)). When different results of ANOVA test including the phospholipid proportions from planktonic bacteria are shown in grey.