Dual Roles of the Conditional Exosomes Derived from Pseudomonas aeruginosa Biofilms: Promoting and Inhibiting Bacterial Biofilm Growth

Antibiotic-resistant biofilm infections have emerged as public health concerns because of their enhanced tolerance of high-dose antibiotic treatments. The biofilm life cycle involves multiple developmental stages, which are tightly regulated by active cell-cell communication via specific extracellular signal messengers such as exosomes. This study was aimed at exploring the roles of Pseudomonas aeruginosa exosomes secreted at different developmental stages in controlling biofilm growth. Our results show that exosomes secreted by P. aeruginosa biofilms during their exponential growth phase (G-Exo) enhance biofilm growth. In contrast, exosomes secreted by P. aeruginosa biofilms during their death/survival phase (D-Exo) can effectively inhibit/eliminate P. aeruginosa PAO1 biofilms up to 4.8-log10 CFU/cm2. The inhibition effectiveness of D-Exo against P. aeruginosa biofilms grown for 96 hours improved further in the presence of 10-50 M Fe3+ ions. Proteomic analysis suggests the inhibition involves an iron-dependent ferroptosis mechanism. This study is the first to report the functional role of bacterial exosomes in bacterial growth, which depends on the developmental stage of the parent bacteria. The finding of D-Exo-activated ferroptosis-based bacterial death may have significant implications for preventing antibiotic resistance in biofilms. Significance statementAntibiotic-resistant bacterial infections caused 1.27 million deaths in 2019 [1], and this number is projected to increase to 10 million deaths annually worldwide by 2050 [2]. Of these infections, up to 80% are caused by biofilm-associated infections [3, 4], which pose a significant challenge to human health. The treatment of biofilm infections remains a formidable problem because of the limited effectiveness of the currently available antibiotics against drug-resistant biofilms [5, 6]. The development of new therapeutic approaches that can effectively combat biofilm infections is required. This study represents a promising solution to antibiotic-resistant biofilm infections. The successful use of exosomes against biofilms opens new possibilities for combating challenging antibiotic-resistant biofilm infections.