THE POTENTIAL OF CULTIVATION CONDITIONS IN THE BACTERIOSTATIC EFFECT OF SOME PGPR ISOLATES AGAINST SOME PATHOGENS

The bioactive metabolites production was studied to optimize the media composition and cultivation conditions for bacterial isolates having antibiosis efficiencies and were identified based on biochemical characteristics and 16S rRNA gene sequencing. The effect of different carbon sources (glucose, glycerol, lactose, mannitol and sucrose), nitrogen sources (ammonium chloride, ammonium nitrate, L-glutamic acid, peptone and sodium nitrate), pH values (4.0-9.5), incubation time (24, 48, 72, 96 and 120 h), temperature (15, 20, 25, 30, 35, 40 and 50oC) and salinity (1.5, 2.5, 3.5, 4.5, 5.5 and 6.5%) on the antibacterial activity were investigated using agar diffusion assay and detected by the zone of inhibition sizes. The antibacterial activity of the tested plant growth promoting rhizobacterial (PGPR) strains, in liquid static culture, strongly impacted by the cultivation conditions, which support considerable antibiosis capabilities for the tested PGPR antagonist's strains, Bacillus altitudinis, Brevibacillus brevis, Paenibacillus xylanexedens and Stenotrophomonas maltophilia, against the test culture of Eschericia fergusonii. The maximum activity was observed at neutral nutrient media (pH 7.0) enriched by glucose as carbon source, L-glutamic acid as nitrogen source with or without 1.5% NaCl salinity and after incubating at 30oC for 48 h, with over 30 mm zone of inhibition against Eschericia fergusonii.