Table 1. Role of surface antigens in sPNAG-based biofilm formation.

	Presence (+) or Absence (−) of O (O16) or K (K1/K92) Antigen
O-Antigen	−	+(O16)	−	−	+(O16)	+(O16)
K-Antigen	−	−	+(K1)	+(K92)	+(K1)	+(K92)
Response to sPNAG	+	−	+	+	+	+

O-antigen production was restored in MG1655 by plasmid pMF19, encoding a functional copy of rhamnosyl-transferase, RfaL, whose gene is mutated in E. coli K-12 [31]. Transformation of MG1655 strain with this plasmid allowed production of O16 antigen [45] confirmed on SDS-PAGE gels (Figure S6, compare lane 8 and 9). For K-antigen, only K1 and K92 capsules were considered. In the case of the K92 capsule, the gene cluster responsible for its biosynthesis was cloned into the pGB20 plasmid and could be easily transferred to any background [46]. As a K1⁺ cell, a K-12-based K-12/K1 hybrid (EV36), generated by conjugation, was used which was capable of producing a polysialic acid capsule indistinguishable from that of natural K1 strains [47]. All the experiments were performed in the MG1655 background except for those corresponding to O16⁻K1⁺ and O16⁺K1⁺ strains, which were in the EV36 background.