Fluorescent Pseudomonas mainly produce the dihydro form of pyoverdine at low specific growth rate

Area of Science:

• Microbiology
• Biochemistry

Background:

• Fluorescent Pseudomonas species produce pyoverdines (PVDs) as siderophores for iron acquisition.
• The conversion of dihydro forms (DHPVDs) to PVDs is crucial for iron uptake but its mechanism is debated.

Purpose of the Study:

• To investigate the influence of cell growth rate and iron concentration on PVD and DHPVD production.
• To elucidate the mechanism of PVD formation from DHPVD in Pseudomonas.

Main Methods:

• Batch and chemostat cultures of three Pseudomonas strains (P. putida, P. fluorescens, P. aeruginosa) were used.
• Pyoverdine and dihydropyoverdine concentrations were quantified using LC ESI-MS and spectrophotometry.
• The ratio of PVD to DHPVD was analyzed under varying growth rates and pH conditions.

Main Results:

• A high PVD-to-DHPVD ratio in pH-controlled batch cultures suggested non-chemical oxidation mechanisms.
• In chemostat cultures, a lower specific growth rate significantly decreased the PVD-to-DHPVD ratio.
• Iron concentration's effect on the ratio was also observed, indicating its regulatory role.

Conclusions:

• The oxidation of DHPVD to PVD is likely catalyzed by an iron-dependent enzymatic reaction.
• Chemical oxidation, particularly base-catalyzed, is unlikely to be the primary mechanism for PVD generation.
• Cellular metabolism and iron availability play critical roles in regulating siderophore production and maturation.