RT Journal Article SR Electronic T1 Increased production of the extracellular polysaccharide Psl can give a growth advantage to Pseudomonas aeruginosa in low-iron conditions JF bioRxiv FD Cold Spring Harbor Laboratory SP 355339 DO 10.1101/355339 A1 Jaime Hutchison A1 Karishma Kaushik A1 Christopher A. Rodesney A1 Thomas Lilieholm A1 Layla Bakhtiari A1 Vernita D. Gordon YR 2018 UL http://biorxiv.org/content/early/2018/06/25/355339.abstract AB In infections, biofilm formation is associated with a number of fitness advantages, such as resistance to antibiotics and to clearance by the immune system. Biofilm formation has also been linked to fitness advantages in environments other than in vivo infections; primarily, biofilms are thought to help constituent organisms evade predation and to promote intercellular signaling. The opportunistic human pathogen Pseudomonas aeruginosa forms biofilm infections in lungs, wounds, and on implants and medical devices. However, the tendency toward biofilm formation originated in this bacterium’s native environment, primarily plants and soil. Such environments are polymicrobial and often resource-limited. Other researchers have recently shown that the P. aeruginosa extracellular polysaccharide Psl can bind iron. For the lab strain PA01, Psl is also the dominant adhesive and cohesive “glue” holding together multicellular aggregates and biofilms. Here, we perform quantitative time-lapse confocal microscopy and image analysis of early biofilm growth by PA01. We find that aggregates of P. aeruginosa have a growth advantage over single cells of P. aeruginosa in the presence of Staphylococcus aureus in low-iron environments. Our results suggest the growth advantage of aggregates is linked to their high Psl content and to the production of an active factor by S. aureus. We posit that the ability of Psl to promote iron acquisition may have been linked to the evolutionary development of the strong biofilm-forming tendencies of P. aeruginosa.