Sugar-binding protein MalE mediates cadmium immobilization and promotes biofilm formation in microbial communities

Microbial communities survive in stressful environments like cadmium (Cd) contamination through adaptive responses. Cd pollution is frequently associated with elevated zinc (Zn); however, how microorganisms utilize Zn to shape community structure remains unclear. Here, we find that Zn enhances Cd(II) immobilization in Paenarthrobacter sp. CC6. Proteomic analysis and heterologous expression identified a sugar-binding protein (MalE) and an energy-related gene cluster ( ansP - acoAB - aceF - menH ) as key contributors to this process. We performed a one-month co-culture of the MalE-expressing strain with various Cd-resistant bacteria. This resulted in enrichment of Chitinophaga sp. CC14 within a synthetic community. Surface-displayed MalE enhanced biofilm formation by CC14, an effect that was abolished when the strains were separated by a membrane. Mass-spectrum analysis showed a concomitant increase in surface maltose on CC14, and point mutation verified that lysine-155 is associated with this interaction. Our findings unveil a MalE-mediated defense system that coordinately links Cd immobilization with biofilm-driven community assembly.