Developing programmable bacterial cell-cell adhesion is of significant interest due to its versatile applications. Current methods that rely on presenting cell adhesion molecules (CAMs) on bacterial surfaces are limited by the lack of a generalizable strategy to identify such molecules targeting bacterial membrane proteins in their natural states. Here, we introduce a whole-cell screening platform designed to discover CAMs targeting bacterial membrane proteins within a synthetic bacteria-displayed nanobody library. Leveraging the potency of the bacterial type IV secretion system-a contact-dependent DNA delivery nanomachine-we have established a positive feedback mechanism to selectively enrich for bacteria displaying nanobodies that target antigen-expressing cells. Our platform successfully identified functional CAMs capable of recognizing three distinct outer membrane proteins (TraN, OmpA, OmpC), demonstrating its efficacy in CAM discovery. This approach holds promise for engineering bacterial cell-cell adhesion, such as directing the antibacterial activity of programmed inhibitor cells toward target bacteria in mixed populations.Cell-cell interactions are crucial in shaping the intricate structures of microbiomes and facilitating essential functions, including genetic exchange, metabolite transfer, and cellular stress responses. The ability to engineer and manipulate such multicellular arrangements not only enhances our understanding of microbial communities but also serves as a basis for developing synthetic platforms, which can enable the development of functional microbial consortia with diverse biotechnological applications 1,2 . For example, multicellular bioconversion represents an area of significant scientific interest, whereby spatially organized microbial communities efficiently convert complex substrates into valuable products 3,4 . Moreover, drawing inspiration from natural biofilms, self-repairing living biomaterials with cell-cell adhesion properties show regenerative capabilities and display improved resilience 3,5 . Furthermore, engineered intercellular adhesion could have profound impacts on targeted manipulations within complex microbial populations, enabling precise and efficient interventions against specific bacteria [6][7][8] .Recent progress in the field of directed cell-cell adhesion has involved the use of bacteria displaying synthetic cell adhesion molecules (CAMs), such as nanobody-antigen or coiled-coil peptide pairs, to facilitate intercellular binding [9][10][11] . These strategies are a rational approach for programming multi-microbial materials. However, despite their potential, certain limitations persist due to restrictions in the number of effective binding pairs that can be deployed for cell-cell adhesion purposes. The current development bottleneck arises from using conventional methods to identify potential binders, such as phage-or yeast-display selection, which were not originally designed to identify functional CAMs for bacteria. These methods often present