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

SOLMI L.; ROSSI F.R.; ROMERO F.M.; RUIZ O.A.; GARRIZ A.

ROSARIO-VIRTUAL

Congreso; REUNION CONJUNTA SAIB-SAMIGE; 2021

SAIB-SAMIGE

Iron is an essential element for most organisms as it takes part in a wide range of cellular processes. Under iron-limiting conditions, many bacteria synthesize and secrete siderophores such as pyoverdine (PVD) to scavenge this element from their surrounding environment and make it available to the cell. Importantly, it has been shown that PVD synthesis and secretion is essential for virulence in Pseudomonas aeruginosa, and that the metabolism of PVD in P. putida is regulated by different nitrogenous compounds including amino acids and polyamines (PAs). PAs are a family of polycations derived from ornithine and arginine playing essential functions in all living organisms. With the purpose to corroborate whether this connection also exists in phytopathogenic Pseudomonas species, in this work we used the model P. syringae pv. tomato DC3000 (Pto) to study the relationship between the metabolism of PAs and iron utilization. When Pto was grown in M9 minimal medium the only PAs detected at the extracellular and intracellular cell environments were putrescine (Put) and spermidine (Spd). Incubation of Pto in an iron-depleted medium supplemented with Spd reduced PVD secretion, whereas this reduction did not occur with Put amendment. These results suggest that siderophore production is negatively regulated by Spd. To analyze in depth the effect 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 iron supplementation, indicating that the utilization of this compound results impaired under PA depletion. However, Spd supplementation promotes the growth of the ∆speE mutant in iron-amended media, while no effect in growth was observed in the ∆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 to maintain iron homeostasis, as even though the supply of iron is required for biochemical demand, the intracellular abundance of this element might lead to iron-induced toxicity. Our future research will try to discern the regulatory mechanisms mediated by Spd that operates on iron utilization in bacteria