Divalent metal ions in microbial envelopes and biofilms

Divalent metal ions, primarily calcium (Ca2+) and magnesium (Mg2+), are fundamental structural components of microbial cell envelopes and the extracellular polymeric substance (EPS) matrix of biofilms (Nikaido, 2003). In Gram-negative bacteria, these cations stabilize the outer membrane by cross-linking the negatively charged phosphate groups of lipopolysaccharide (LPS) molecules, thereby preventing electrostatic repulsion and maintaining membrane integrity (Nikaido, 2003). Within the biofilm environment, divalent ions act as "ionic glues" that facilitate the cross-linking of extracellular DNA (eDNA), proteins, and polysaccharides, which is essential for the mechanical stability and cohesion of the biofilm (Körstgens et al., 2001; Whitchurch et al., 2002). These ions also play roles as enzymatic cofactors for various microbial processes (Banin et al., 2006). In the context of disease, the stabilization of biofilms by these ions contributes to the persistence of chronic infections, such as those found in cystic fibrosis or on indwelling medical devices, by protecting bacteria from host immune defenses and limiting antibiotic penetration (Finnegan & Percival, 2015). Therapeutic agents like EDTA and citrate target these ions through chelation, which removes the ions from the matrix and envelope, leading to biofilm dissolution and increased bacterial susceptibility to antimicrobial treatments (Finnegan & Percival, 2015). This strategy is particularly effective in disrupting recalcitrant biofilms in clinical settings like chronic wound management (Percival et al., 2005).

Other names

Divalent cationsCa2+ and Mg2+ in biofilmsEPS-associated metal ionsStructural metal ions

Chelation of divalent cations (primarily Ca2+ and Mg2+) leads to the disruption of ionic bridges that stabilize the microbial outer membrane and the extracellular polymeric substance (EPS) matrix, resulting in increased membrane permeability and biofilm dissolution (Finnegan & Percival, 2015; Nikaido, 2003).