FIG 5.

A model for P. aeruginosa-Streptococcus interactions. P. aeruginosa has both positive and negative interactions with Streptococcus spp. (A) It has been demonstrated previously that P. aeruginosa can enhance S. parasanguinis biofilm formation through alginate secretion (24) or inhibit Streptococcus growth via rhamnolipid secretion (23). Here we propose a negative interaction wherein iron sequestration by P. aeruginosa limits Streptococcus sp. growth. Streptococcus-promoting factors produced by P. aeruginosa have not yet been identified (indicated by the question mark). (B) Previous evidence also demonstrates that streptococci can influence P. aeruginosa through AI-2 signaling (18), leading to enhanced lasB, rhlA, exoT, and phzA1/2 gene expression, or can inhibit P. aeruginosa viability through H₂O₂ production (16, 20, 21) and subsequent generation of reactive nitrogenous intermediates (20, 21).