(231k) Effect of Dissolved Oxygen on the Cell Growth and Spore Production of Bacillus Thuringiensis in Semi-Industrial Scale Bioreactor

In controlling the insect pest in agriculture and insect vectors that lead to human disease, there had been application of chemical insecticides. The use of these chemical pesticides had led to several problems including environmental problem and give effects on human health such as cancer and several immune system disorders. Chemical agents are also probable to lead to emergence of insect resistance and have a long residual effect with toxicity to non-target organisms. Therefore, as an alternative of biocontrol agents, Bacillus thuringiensis-based biopesticides had been used as biopesticide in controlling the agricultural pest. Large quantities of bio insecticides possess high insecticidal activity, produced by fermentation, are required for practical applications of bio insecticides. For industrial production, they prefer medium that have lowest cost and give high quality of insecticidal function. To investigate the effects of Dissolved Oxygen Control (DOC) on the cell growth and spore production of B. thuringiensis. DOC was controlled at three different levels of uncontrolled DOC, 10, and 30 % of air-saturation by manipulating agitation speed and airflow in a series of batch cultivation in the semi-industrial scale bioreactor. For uncontrolled DO which was started at 100 % at the beginning of cultivation and was not controlled throughout the cultivation. This cultivation showing a significant loss in cell mass due to limitation of DO at 3 to 6 hour of cultivation, this was attributed to cell lysis and the spore formation was only 6.5 x 10⁷ cfu mL^-1 after 45 hours cultivation when there was no cell growth observed at this phase. No big differences on the cell growth and spore production were observed when the DOC was controlled at 10 %. Unfortunately, when DOC was controlled at 30 %, the highest cell mass was 20.93 g L^-1 after 16 hours cultivation and then start to enter death phase after 24 hours cultivation with the specific growth rate of 0.07 h^-1. The cell mass production was increased up to 103.96 % when compared with growth without controlling the DO. However, the sporulation productivities was increased when the DOC was controlled at 30 % to 2.15-fold about 115.38 %.