THE POLYAMINE SPERMIDINE REGULATES IRON UTILIZATION AND PYOVERDINE SECRETION IN Pseudomonas syringae

SOLMI L; ROSSI FR; ROMERO FM; RUIZ OA; GÁRRIZ A

Congreso; Reunión SAIB-SAMIGE; 2021

Iron is an essential element for most organisms as it takes part in a wide range of cellular processes. Under iron-limitingconditions, many bacteria synthesize and secrete siderophores such as pyoverdine (PVD) to scavenge this element from theirsurrounding environment and make it available to the cell. Importantly, it has been shown that PVD synthesis and secretion isessential for virulence in Pseudomonas aeruginosa, and that the metabolism of PVD in P. putida is regulated by differentnitrogenous compounds including amino acids and polyamines (PAs). PAs are a family of polycations derived from ornithineand arginine playing essential functions in all living organisms. With the purpose to corroborate whether this connection alsoexists in phytopathogenic Pseudomonas species, in this work we used the model P. syringae pv. tomato DC3000 (Pto) to studythe relationship between the metabolism of PAs and iron utilization. When Pto was grown in M9 minimal medium the onlyPAs detected at the extracellular and intracellular cell environments were putrescine (Put) and spermidine (Spd). Incubationof Pto in an iron-depleted medium supplemented with Spd reduced PVD secretion, whereas this reduction did not occur withPut amendment. These results suggest that siderophore production is negatively regulated by Spd. To analyze in depth theeffect of PA depletion on iron utilization, we constructed two mutant strains lacking genes involved in the synthesis of Put(∆speA∆speC) and Spd (∆speE). Both mutant strains were affected on PVD secretion during iron-limiting conditions.Additionally, no significant increments in growth were observed in the ∆speE and ∆speA∆speC strains in response to ironsupplementation, indicating that the utilization of this compound results impaired under PA depletion. However, Spdsupplementation promotes the growth of the ∆speE mutant in iron-amended media, while no effect in growth was observed inthe ∆speA∆speC strain after Put addition. Deficiency on PDV secretion and iron utilization in mutant strains were restored by genetic complementation. These contrasting effects of Spd in PDV secretion and iron utilization might be crucial tomaintain iron homeostasis, as even though the supply of iron is required for biochemical demand, the intracellular abundanceof this element might lead to iron-induced toxicity. Our future research will try to discern the regulatory mechanisms mediatedby Spd that operates on iron utilization in bacteria