Characterization of Distinct Biofilm Cell Subpopulations and Implications in Quorum Sensing and Antibiotic Resistance

Abstract

ABSTRACT Bacteria change phenotypically in response to their environment. Free swimming cells transition to biofilm communities that promote cellular cooperativity and resistance to stressors and antibiotics. We uncovered three subpopulations of cells with diverse phenotypes from a single-species Pseudomonas aeruginosa PA14 biofilm, and used a series of steps to isolate, characterize, and map these cell subpopulations in a biofilm. The subpopulations were distinguishable by size and morphology using dynamic light scattering (DLS) and scanning electron microscopy (SEM). Additionally, growth and dispersal of biofilms originating from each cell subpopulation exhibited contrasting responses to antibiotic challenge. Cell subpopulation surface charges were distinctly different, which led us to examine the ionizable surface molecules associated with each subpopulation using mass spectrometry. Matrix assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry analysis of cell subpopulations revealed ions unique to each subpopulation of cells that significantly co-localized with ions associated with quorum sensing. Transcript levels of algR, lasR, and rhlI in subpopulations isolated from biofilms differed from levels in planktonic stationary and mid-log cell subpopulations. These studies provide insight into diverse phenotypes, morphologies, and biochemistries of PA14 cell subpopulations for potential applications in combating bacterial pathogenesis, with medical, industrial, and environmental complications. IMPORTANCE Pseudomonas aeruginosa biofilms can cause chronic infections in burn wounds, grow on medical equipment, and proliferate in the lungs of people with cystic fibrosis. These inherently antibiotic tolerant biofilms are difficult to eradicate largely due to the complexity of the biofilm environment. Developing more effective biofilm treatments is reliant upon understanding biofilm heterogeneity. We identified and characterized three separate cell subpopulations found in P. aeruginosa PA14 biofilms. The distinct morphologies, phenotypes, and biochemistries of each of these cell subpopulations indicate that they contribute differently to the overall biofilm environment. These findings demonstrate that bacterial cells of the same species exhibit diversity that implies distinct roles in biofilm initiation, maturation, and maintenance.

Keywords

• Pseudomonas aeruginosa
• antibiotic tolerance
• biochemistry
• biofilms
• mass spectrometry
• morphological variation