Abstract
Bacteria associated with rhizosphere are recognized as highly diverse bio control agents. Production of antagonistic
substances by such bacteria has significance in the control of phytopathogenic microorganisms. Pseudomonas aeruginosa
SA 188, an indigenous isolate from rhizosphere was found to produce a high molecular weight pyocin which was resistant to
proteolytic enzymes (protease, proteinase K, pepsin, papain and lipase). This pyocin exhibited antibacterial activity against
both the Gram-positive and Gram-negative bacterial strains including Corynebacterium xerosis, Listeria monocytogenes,
Micrococcus luteus, Staphylococcus aureus, Streptococcus pyogenes and Escherichia coli. The production of this pyocin by
P. aeruginosa SA 188 started in the early logarithmic phase of the growth cycle and reached maximum at the late log phase.
A single peak of protein was demonstrated by size exclusion chromatography (using Sephadex G-75 column). There was an
increase in the specific activity after each step of purification and the final purification of pyocin SA 188 was found to be 4.6
folds. Electrophorogram of this protein revealed a single band of molecular mass approximately 45 kDa by SDS-PAGE
(10% acrylamide denaturing gel). The band was found bioactive in the direct gel overlay.
