Influence of magnesium ions on biofilm formation by Pseudomonas fluorescens

SummaryMg2+ can potentially influence bacterial adhesion directly through effects on electrostatic interactions and indirectly by affecting physiology-dependent attachment processes. However, the effects of Mg2+ on biofilm structure are largely unknown. In this study, Pseudomonas fluorescens was used to investigate the influence of Mg2+ concentration (0, 0.1 and 1.0 mM MgCl2) on biofilm growth. Planktonic and attached cells were enumerated (based on DAPI staining) while biofilm structures were examined via confocal laser scanning microscopy and three-dimensional structures were reconstructed. Mg2+ concentration had no influence on growth of planktonic cells but, during biofilm formation, Mg2+ increased the abundance of attached cells. For attached cells, the influence of Mg2+ concentration changed over time, suggesting that the role of Mg2+ in bacterial attachment is complex and dynamic. Biofilm structures were heterogeneous and surface colonization and depth increased with increasing Mg2+ concentrations. Overall, for P. fluorescens, Mg2+ increased initial attachment and altered subsequent biofilm formation and structure.