Horizontal gene transfer is a major driver of bacterial adaptation, enabling the acquisition of new functions, pathogenicity islands, or antibiotic resistances. Among its natural mechanisms, genetic transformation is unique in being entirely driven by the recipient cell: it captures high-molecular-weight exogenous DNA, transports it across its envelope, and integrates it into its own chromosome by homologous recombination. This ability is only possible when the bacterium enters a differentiated state termed competence. In *Bacillus subtilis*, a model Gram-positive organism studied for decades, entry into competence relies on a signal transduction system that culminates in the activation, by the regulator ComK, of approximately one hundred late genes. Yet, despite this level of knowledge, the identity of the extracellular factor responsible for the very first step—the binding of DNA to the surface of competent cells—remained unknown. Previous work had only established that, unlike in *Streptococcus pneumoniae*, the pseudopilus plays no role here, with the cytoplasmic protein ComGA remaining the only indispensable factor identified.
This study identifies wall teichoic acids (WTA), anionic glycopolymers covalently attached to peptidoglycan and associated with numerous critical functions in Gram-positive bacteria, as players in this initial step. The approach combined the use of cell-wall-targeting antibiotics—notably tunicamycin, an inhibitor of WTA synthesis—with fluorescence microscopy, tracking fluorophore-labeled exogenous DNA and visualizing surface polymers. Transformation efficiency measurements, based on the enumeration of tetracycline-resistant transformants relative to the number of viable cells, complemented these observations, as did transcriptional fusions to luciferase.
The authors show that competence-specific WTA are produced and distinctively localized in competent cells, where they mediate DNA binding in the vicinity of the transformation machinery, near the foci formed by ComGA. They further propose that TuaH, a putative glycosyltransferase induced during competence, modifies these WTA to promote, directly or indirectly, DNA binding. The resulting model distinguishes vegetative WTA from competence-specific WTA: the former, present at the surface of non-competent cells, hinder DNA binding, whereas the latter, finely remodeled, create high-affinity binding sites. Based on these findings and existing knowledge, the team thus establishes a model of DNA binding and transport during genetic transformation in *B. subtilis*.