Pam binds to EPS in the JQ-EZ-05 solubility dmso extracellular GSK1210151A in vivo matrix and modifies cell attachment To investigate the localization of Pam in P. luminescens TT01 cells, sections of bacterial colonies were observed under transmission electron microscopy (TEM) revealing large amounts of exopolysaccharide (EPS)-like matrix filling the spaces between cells (Fig. 4A). We used immunogold localization of Pam in these sections and found that the protein is associated with this extracellular material that is distributed surrounding the cells (Fig. 4B). In TT01pam the EPS-like material was still present but we did not see specific binding of the antibody (Fig. 4C), suggesting that although Pam binds to the extracellular matrix, it does not

significantly alter its production or general structure. Furthermore, Western-blot analysis using the anti-Pam antibody revealed that Pam could be detected in crude EPS preparations (Fig 4D), confirming that from all the extracellular matrix components Pam binds at least to EPS. Our studies revealed that EPS-bound Pam can be released by the action of SDS and salt (KCl) but not by mechanical disruption (vortex) (data not shown). Figure 4 Pam localization on bacterial cells. (A) Micrograph PND-1186 concentration of a cross-section from a P. luminescens TT01 colony observed by TEM. Note the presence of an extensively folded extracellular matrix (black arrow) between the bacterial cells (indicated with

P). (B) Immunolocalization of Pam using the anti-Pam antibody and a conjugated-gold secondary antibody. Gold particles extensively decorate the fibrillar EPS-like matrix (black arrow). (C) The TT01pam strain shows no anti-Pam antibody signal but the fibrillar

matrix is still present. Scale bars are 0.2 μm. (D) Western blot confirming the presence of Pam in preparations of crude EPS. Lane 1: crude EPS extracted from TT01rif, lane 2: EPS from TT01pam and lane 3: purified recombinant Pam. As Pam binds to EPS and EPS has been shown to be important in biofilm formation [11], we investigated the possibility that Pam influences the different stages of biofilm formation. Pellicle assays and biofilm growth in microscopy chambers did not show differences in mature biofilm formation between TT01rif and TT01pam (data not shown). To analyze the influence of Pam on the early steps of biofilm formation, namely Ribonucleotide reductase initial attachment, we looked at attachment of the two strains to glass coverslips when cultured ex vitro in hemolymph plasma. As shown in Figure 5, the parental TT01rif cells attached in greater numbers than TT01pam to the glass surface in hemolymph, but not in LB medium or Schneiders insect growth medium (data not shown). Importantly, we were also able to detect Pam in cell and supernatant fractions in bacteria grown in hemolymph plasma at 8 hours. Figure 5 Comparison of bacterial attachment to surfaces in presence of insect hemolymph by fluorescence microscopy between TTO1rif and the pam mutant.