Influence of iron(III) and pyoverdine on extracellular proteinase and lipase production by Pseudomonas fluorescens B52

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Abstract
Factors associated with the production of extracellular lipase and proteinase by Pseudomonas fluorescens B52 during the late-log, early-stationary phase of grown were examined. Active lipase production by resting cell suspensions was observed when cells were harvested during the log phase (A600 of 0.3–0.9) Resting suspensions of younger cells (A600P. fluorescens RM14 to B52 cells at low density resulted in stimulation of lipase and proteinase production. Similar results were found using cell-free culture fluid of RM14. Gel filtration on Biogel P2 revealed that the stimulatory factor co-chromatographed with the iron(III) siderophore, pyoverdine. Partially purified pyoverdine stimulated enzyme synthesis at a concentration of 6 μM while having no effect on activity of preformed enzyme. Production of pyoverdine and extracellular enzymes was also stimulated by transferrin, a strong iron(III) binding protein. Growth of B52 in deferrated media was limited to 27% of that found with untreated media. Maximum pyoverdine, proteinase and lipase synthesis was obtained at a final iron(III) concentration of 5.75 μM. Growth was maximal in 8.75 μM iron(III) while synthesis of pyoverdine, proteinase and lipase was reduced to 3.6, 6.6 and 30% respectively in 23.75 μM iron(III). Lipase activity in cell-free culture fluid was slightly inhibited by the addition of up to 400 μM iron(III) while proteinase activity was unaffected. In dilute cell suspensions, lipase synthesis was more sensitive to iron(III) than was proteinase (50% inhibition at 1.6 μM and a maximum of 40% inhibition at 5.0 μM, respectively). In the case of lipase, added pyoverdine was able to partially protect enzyme production from the effects of iron(III). The results are consistent with a role for iron(III) in the regulation of extracellular lipase and proteinase synthesis by P. fluorescens.