Iron-reglulated secreted A (IrsA) protein of 144 aas with 1 N-terminal TMS. Legionella pneumophila (cause of Legionnaires' disease) secretes IrsA, an iron-regulated exoprotein that facilitates bacterial growth in low-iron conditions and modulates biofilm formation (Lopez et al. 2024).  IsrA is transcriptionally regulated by Fur and encodes a ~15 kDa protein. It was present in all L. pneumophila strains examined and had homologs in a subset of the other Legionella species. Compatible with it containing a classic signal sequence, the protein was detected in bacterial culture supernatants in a manner dependent upon the L. pneumophila type II secretion system.  It had growth-enhancing activity after examining an Lp02 mutant that lacked both IrsA and the Fe²⁺-transporter FeoB. The irsA mutant of 130b, but not its complemented derivative, did, however, display increased biofilm formation on both plastic and agar surfaces, and compatible with this, the mutant hyper-aggregated (Lopez et al. 2024).