[19] who reported that the antimicrobial agent produced by Pseudomonas species MCCB was stable after autoclaving at 121°C for 20 min even though there #AZD3965 purchase randurls[1|1|,|CHEM1|]# was a significant reduction in activity. Uzair et al. [20] also reported

the thermal stability of an antimicrobial agent produced by Pseudomonas aeruginosa at a temperature of 121°C for 20 minutes. However, Roitman et al. [21] showed that variations in the fermentation medium often results in changes in the composition of the antibiotics produced. The differences in the thermal stability of the antimicrobial agents produced in this study as compared to other studies may therefore be due to differences in some nutritional and or physical factors which led to the production of metabolites that are thermolabile at temperatures beyond 100°C. Our results also showed that nine days incubation period was optimum for maximum antibacterial activity by MAI2, an indication of maximum antibiotic production, after which there was no significant increase. Several other factors influence production of secondary metabolites by microorganisms, the most important one being the composition of the fermentation medium [22]. Sole et al. [23] noted that glucose can be used as a source for bacterial growth while repressing the production of secondary metabolites. The isolate (MAI2) utilised glycerol and starch best

for maximum production of the antimicrobial metabolites. Nitrogen is very vital in the synthesis of enzymes involved in primary and secondary metabolism Selleck BVD-523 [24]. Therefore depending on the biosynthetic pathways involved, nitrogen sources may affect antibiotic formation. Shapiro [25] noted that the type of nitrogen source (organic or inorganic) plays

a role in the synthesis of secondary metabolites. Phosphoprotein phosphatase Charyulu and Gnanamani [26] reported that Pseudomonas aeruginosa MTCC 5210 utilized organic nitrogen source for better yield of antimicrobial metabolites than the inorganic sources. These observations are consistent with the findings of this study as asparagine was better used for antibiotic production by MAI2 than the inorganic nitrogen sources (sodium and potassium nitrates and the ammonium salts) employed. Generally, the intracellular pH of most microorganisms is maintained near neutrality regardless of the pH in the outside medium [27]. However as the proton gradient across the cytoplasmic membrane increases, the cells commit more of their resources towards maintaining the desired intracellular pH [28], thus changes in external pH affect many cellular processes such as growth and the regulation of the biosynthesis of secondary metabolites [29]. The highest activity of the antimicrobial metabolite by the strain was at pH 7. This result agrees with a study carried out by Charyulu and Gnanamani [26] who reported maximum production of metabolite by Pseudomonas aeruginosa MTCC 5210 at pH 7.