Effect of Dose-Response of Zinc and Manganese on Siderophores Production

Problem statement: This study was conducted to find and determine whether the siderophores of the four environmental Pseudomonas spp. isolates possess a sequestering activity towards essential transition metals (Zn and Mn) other than iron. Approach: Four fluorescent Pseudomonads isolated from various environments, were characterized analytically (Isoelectric focusing), biologically (pyoverdine-mediated uptake) and genetically (16S rDNA sequencing). By means of spectrophotometric measurements, it was possible to establish and compare the levels of pyoverdine production, in two different nutrient-poor media. Results: The strains were assigned, by sequencing, to P. fluorescens, P. aeruginosa, P. putida and P. mosselii isolated, respectively from soil, compost, sea water and waste water treatment plant. These bacterial strains were recognized as producing diver’s yellow-green siderophores types, when grown under conditions of iron starvation. The highest metabolite concentration was obtained with PsC132 and PsTp171 strains isolated respectively from compost and waste water treatment plant, in CAA medium. Strains grown in CAA medium exhibit a higher PVD level compared to SM medium. Mn (II) was found to promote pyoverdine biosynthesis, but rather, Zn (II) had no significant effect on siderophore production when compared to control medium. For both strains PsS29 and PsC132, the increase of iron concentration quenched siderophore production especially above 20 μM. Pyoverdine level declined with the high concentration of zinc but increased with Manganese concentration ranging up to 70 μM (in case of PsC132) and 300 μM (in case of PsS29). Conclusion/Recommendations: The ability of fluorescent Pseudomonas, isolated from wastewater treatment plant and from compost, to sequester zinc, point to a unique advantage of these species for divers bioremediation applications.