Effect Of Some Antibiotics On Iron Regulation Of Fluorescent Siderophore(Pvd)

Antibiotics are secondary metabolites or synthetic analogs of pathogens produced by bacteria,molds or other microorganisms.They are widely used to treat various bacterial infections or diseases caused by pathogenic microorganisms.For antibiotics,some will remain in the body causing the drug residues;the other part will be metabolized with the body goes into the environment.Pseudomonas will secrete fluorescent iron carrier Pvd in the case of iron deficiency that can mediate iron absorption of Pseudomonas.Great progress has been made in the study of the absorption and regulation of iron about Pseudomonas.However,the effect of antibiotics on iron absorption about Pseudomonas is needed to be further studied.Therefore,we selected broad spectrum of antibiotics,tetracycline and ciprofloxacin,and studied the effect of ciprofloxacin and tetracycline on the interaction between Pvd and Fe³⁺using Tb³⁺as a fluorescent probe.Firstly,we studied the interaction of tetracycline and ciprofloxacin with Tb³⁺by UV-vis,fluorescence,fluorescence lifetime and isothermal titration calorimetry.The results showed that tetracycline and Tb³⁺bound at a ratio of2:1 while ciprofloxacin and Tb³⁺bound at a ratio of 3:1.The characteristic sensitization peak of Tb³⁺is generated at about 544nm upon ciprofloxacin,and it is beneficial to explore the effect of ciprofloxacin on the interaction of Tb³⁺and Pvd.In addition,the interactions between tetracycline and ciprofloxacin with Fe³⁺are also studied.The same method was used to show that tetracycline binds to Fe³⁺in a ratio of 1:1 and ciprofloxacin also binds to Fe³⁺in a ratio of 1:1.In addition,the results indicated that both CIP and TC can bind to the cyclic peptide portion of Pvd,the binding ratio was 1:1,and the binding constants were?8.90±0.01?×10³ L/mol,?7.41±0.01?×10⁴ L/mol.Secondly,we studied the interactions of tetracycline,ciprofloxacin with Pvd and Tb³⁺.Similarly,the interaction between tetracycline,ciprofloxacin and Pvd,Tb³⁺were studied by UV-vis absorption,fluorescence emission,fluorescence lifetime and isothermal titration calorimetry.According to different characteristic sensitization and different binding constants of CIP and Pvd to Tb³⁺,the formation of Pvd-Tb³⁺-CIP ternary complex was obtained,and isothermal titration calorimetry further proved that the reaction is entropy-driven spontaneous reaction,while Pvd-Tb³⁺-TC ternary complex is an endothermic,entropic-driven spontaneous reaction.Finally,the effects of tetracycline and ciprofloxacin on the interaction between Pvd and Fe³⁺were studied.Similarly,CIP and TC do not form Fe³⁺-centered ternary complexes with Pvd-Fe³⁺after binding of Pvd to Fe³⁺at 1:1 by UV-vis absorption spectra,fluorescence emission spectra,fluorescence lifetime and isothermal titration calorimetry.However,it binds to the peptide of Pvd with weak interaction to form a complex centered on Pvd.The binding ratio of Pvd-Fe³⁺to CIP and TC is close to 1,and the binding constants are?3.16±0.01?×10² L/mol,?1.07±0.02?×10³ L/mol,respectively.That is,although CIP and TC hardly affect the binding of Pvd to Fe³⁺,it does affect the cyclic peptide portion of Pvd,which may affect the binding to the Pvd receptor protein.