Cadmium Stress Favours Biofilm Cooperation and Polysaccharide-Enriched Matrix Remodelling in Bacterial Consortia

Environmental stressors trigger complex adaptations in microbial communities, yet the associations between social network dynamics and metabolic strategies remain poorly understood, limiting our ability to design robust synthetic microbiomes. Here, we show that Cd stress was associated with structural simplification of soil bacterial co-occurrence networks, characterized by a 48.5% reduction in connectivity. In vitro assays further revealed a 93% increase in cooperative interactions within biofilms under Cd exposure. This shift in biofilm-associated cooperation coincided with altered physiological patterns, including a 45.9% increase in EPS synthesis and a 13.7% decrease in community CO₂ emissions. Crucially, our analysis suggests that the intensity of cooperative interactions was associated with specific extracellular matrix allocation patterns. High-intensity cooperation was linked to a higher proportion of polysaccharide-rich matrices, which improved the stability and efficiency of Cd sequestration in vitro. Leveraging these interaction-informed patterns, we assembled a synthetic core consortium that modulated the rhizosphere microbiome in a proof-of-concept hydroponic system and reduced Cd accumulation in rice leaves by 52.9%. These findings support a conceptual framework in which biofilms may act as sites of social integration and altered extracellular matrix production, offering an interaction-informed basis for assembling stress-resilient microbiomes.