ABSTRACT

The study assessed the optimization of growth conditions of the Bacillus isolates, they were evaluated using various parameters such as pH, carbon source and sodium chloride (NaCl) concentration. A total of four (4) isolates of Bacillus megaterium were isolated from the rhizosphere of tomato plants and identified using phenotypic and biochemical characterization. The growth rate of each isolate after 24hr incubation was measured using spectrophometer at optical density of 540nm. Data were subjected to One-Way ANOVA followed by Duncan posthoc test at p<0.05. Results showed that maximum growth ofthe bacterium isolates was notable at pH of 7.0 while the isolates barely tolerated growth at pH 3.5 and 5.0. Bacillus megaterium I isolate showed a significant (p<0.05) increase in the growth as the salt concentration was increased. Thus, the highest growth was observed. Bacillus megaterium II isolate had a different growth pattern as increase in salt concentration from 1% to 3% resulted in an increase in growth of the isolate, while further increase in salt concentration from 3% to 5% led to a significant (p<0.05) decrease in growth. The sucrose showed maximum significant (p<0.05) growth of bacteria (1.83±0.28a) when compared to starch (1.10±0.01b) and lactose (1.15±0.01b). The starch showed lowest bacterial growth. In conclusion, the optimization methods are believed to be effective and powerful approach for screening key factor for microbial growth in different stress condition. The activity and stability of an organism is influenced by the type ofstrain, cultivation conditions (temperature, pH, aeration, agitation, incubation time) and the growth medium composition (carbon and nitrogen sources).