FIG. 8.

Model of the GacA/RsmA signal transduction pathway in P. aeruginosa PAO1. Expression of the untranslated regulatory RNA RsmZ depends on the presence of GacA. The function of RsmZ is to antagonize the action of the small RNA-binding protein RsmA. RsmA positively controls rsmZ expression, thus forming a negative autoregulatory circuit whose mechanism is not understood at present. RsmA also negatively controls AHL-dependent quorum sensing as well as a number of quorum-sensing-dependent genes, some of which code for secondary metabolites and virulence determinants; these are regulated indirectly at the transcriptional level via quorum sensing but probably also directly at the translational level, as is the case for hcnA (42). Lipase and rhamnolipid production are controlled positively by RsmA, independently of the quorum-sensing control. Dotted line, modulating negative effect; solid bar, negative effect; arrow, positive effect.