Cell-surface signalling is a sophisticated regulatory mechanism used by Gram-negative bacteria to sense signals from outside the cell and transmit them into the cytoplasm. This regulatory system consists of an outer membrane-localized TonB-dependent receptor (TonB-dependent transducer), a cytoplasmic membrane-localized antisigma factor and an extracytoplasmic function (ECF) sigma factor. Pseudomonas aeruginosa contains 13 potential surface signalling systems of which only six have been studied in detail. In this work we have identified the regulons of five novel P. aeruginosa signalling systems. For that, the ECF sigmas PA0149, PA1912, PA2050, PA2093 and PA4896 have been overexpressed and their target gene candidates have been identified using DNA microarray, proteomic analysis, and/or lacZ reporter construct. All five ECF sigma factors control the production of one TonB-dependent transducer. Interestingly, two sigma factors, PA2050 and PA2093, regulate the synthesis of a second transducer. Furthermore, we show that although all these sigma factors seem to control putative (metal) transport systems, one of them also regulates the expression of P. aeruginosa pyocins. Finally, we also show that the PA1912-PA1911-PA1910 (designated FemI-FemR-FemA in this work) signalling system responds to the presence of the Mycobacterium siderophores mycobactin and carboxymycobactin and is involved in the utilization of these heterologous siderophores. © 2007 The Authors.