Figure 2
Growth-inhibitory function of meningococcal TpsA. (A) Cells of an unencapsulated derivative of strain B16B6, carrying a plasmid with a chloramphenicol-resistance marker, were mixed 1:1 with cells of ΔtpsA-tpsC, ΔtpsB or ΔtpsC 2-5 mutants, all carrying a kan cassette. The suspensions were spotted on GC plates without antibiotics and incubated for various time periods. In the experiment with the ΔtpsC 2-5 mutant as the target cells, the suspensions were only spotted after 0 and 48 hours. The ratios of the ΔtpsA-tpsC (grey bars), ΔtpsB (white bars), or ΔtpsC 2-5 (hatched bars) mutants over wild-type bacteria in the spots was determined by plating on GC media containing kanamycin or chloramphenicol and counting colony-forming units after overnight incubation. (B) A rifampicin-resistant derivative of the unencapsulated B16B6 strain was mixed 1:1 with the ΔtpsA-tpsC mutant harboring plasmid pFPIORF1, which contains the first IORF of B16B6 under the control of an IPTG-inducible promoter. The bacteria were incubated in the presence or absence of IPTG for 24 hours as above. The ratio of the ΔtpsA-tpsC mutant over the wild-type bacteria was determined as described. Results are means and s.d. of three independent experiments. All the strains tested here did not show differences in viability when grown separately.