Characterization of Staphylococcus lugdunensis biofilm reveals key differences according to clonal lineage and iron availability

To understand the mechanisms involved in the evolutionary success of Staphyloccocus lugdunensis clones, we compared the biofilm-forming ability of representative strains of the seven clonal complexes (CCs) in rich and iron-restricted conditions, and characterized the extracellular matrix (ECM) of two highly biofilm-forming strains under each condition. Over 90% of the 49 S. lugdunensis strains produced biofilm in both conditions, with a level of production depending on the iron availability and clonal lineage. Two behaviors were observed: a significantly higher production in rich medium than in iron-restricted medium for CC1, CC2, and some CC3 strains, and the opposite phenomenon for CC6 ones. Analysis of the ECM of two representative strains using confocal microscopy showed that biofilm of the CC3 strain in rich medium contained similar amounts of proteins, eDNA and polysaccharides while that of CC6 strain was predominantly proteinaceous. Under iron-restricted conditions, biofilm structure and composition of both strains completely differed from those obtained in rich conditions. The proteomic analysis of their biofilm ECM by liquid chromatography coupled to tandem mass spectrometry identified 321 proteins common to both strains, mainly intracellular and in particular ribosomal. Of note, 202 proteins differed between the strains in terms of abundance, with a higher proportion of membrane proteins in the CC3 strain. This study performed on a large cohort of strains shows that S. lugdunensis biofilm-forming capacity is strongly associated with CC and iron availability. This analysis of biofilm-associated proteins in S. lugdunensis opens the way to propose new molecular targets for anti-biofilm strategies.