Studies of Growth Conditions and Estimation of Oxygen Uptake Rate for Bacillus Thuringiensis Fermentations

95 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1993.Oxygen uptake rates (OUR) for Bacillus thuringiensis were determined by dynamic measurements using a dissolved oxygen electrode. On-line estimation of OUR was achieved for a 2-1 fermentor. The dynamics of a dissolved oxygen electrode was important to the accuracy of estimation. Various approaches to estimate OUR were tested. In non-aeration phases, the least squares method was used to determine the values of OUR. For high oxygen demand situations, the data collected in re-aeration phases were analyzed by the least squares method and conjugate directions method to calculate OUR. It was found that the values of OUR obtained from the conjugate directions method were closer to those from the least squares in non-aeration phases.Monitoring the values of OUR during B. thuringiensis batch cultivations revealed the lag, exponential growth, stationary, and sporulation phases. In batch cultivations, the optical density of cultivation mixture was correlated to the OUR with a second order linear regression model during exponential growth phases. The regression model was used to predict the optical density. For a well sporulated batch cultivation, the OUR was found to decrease linearly with time during sporulation. The relationship between specific oxygen uptake rates and specific growth rates were found to be linear in a continuous stirred tank reactor (CSTR) cultivation. The yield for cells produced per unit oxygen was about $5.0\times10\sp $ cells/g O$\sb2$.Among the temperatures and pH values tested, it was found that the highest specific growth rate (1.37 h$\sp{-1}$) and highest final spore count $(1.4\times10\sp9$ CFU/ml) for batch cultivations occurred at 32$\sp\circ$C and pH 7. It was found that glucose did not limit the growth of B. thuringiensis. However, cells needed more oxygen to maintain life when glucose was absent.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD