Bacterial coaggregation, the specific recognition and adhesion of genetically distinct microbial cells, plays a key role in the formation and architecture of multispecies biofilms. This study aimed to identify new coaggregating strains and explore the mechanisms underlying coaggregation, as well as their influence in biofilm development, structure, and matrix composition.
Five bacterial strains from different environmental origins were tested in 15 pairwise combinations. Visual aggregation assays identified Escherichia coli ATCC 25922 as a novel coaggregating strain. The positive coaggregating pairs were further evaluated for their ability to form biofilms. To explore the contribution of secreted metabolites to biofilm development, cell-free supernatants from the coaggregating strain were added to biofilms. Additionally, a non-coaggregating E. coli strain was included as a control to distinguish metabolic effects from those associated with coaggregation capacity. While coaggregation influenced certain biofilm characteristics, such as increased heterogeneity and roughness, the most significant findings emerged from the analysis of supernatant effects. Supernatants from both coaggregating and non-coaggregating strains significantly impacted biofilm thickness, culturability, and the composition of extracellular polymeric substances (EPSs), particularly increasing polysaccharide and lipid content. Notably, these effects were not exclusive to coaggregating strains, suggesting that the secreted metabolic products of each strain are more critical than coaggregation capacity in shaping biofilm outcomes.
The overall results highlight the importance of cell–environment communication in microbial ecology and provide new insights directly relevant to urban water systems. By identifying Escherichia coli ATCC 25922 as a new coaggregating strain and demonstrating that extracellular metabolites play a more decisive role than physical coaggregation in modulating biofilm development and matrix composition, this study open up perspectives for innovative biofilm control strategies in water distribution networks, contributing to improved water quality management while reducing dependence on chemical disinfectants.
