MODELS FOR GROWTH OF BACTERIA INOCULATED INTO STERILIZED SOIL

Abstract

We developed a series of simulation models of increasing complexity to describe the growth of bacteria inoculated into sterilized soil. Variables considered in the models included bacterial carbon (C) and nitrogen (N), CO2 evolved, soil NH4+, and added glucose. An optimization procedure was used to determine the best possible fit of each model to the data. This use of optimization allowed an objective comparison of the success of various model formulations. The analysis suggested that early rapid growth in sterilized soil was largely at the expense of a pool of nitrogenous soluble organic material (organic C-N) made available by sterilization. Growth rate and yield were high until the organic C-N was exhausted, after about 1 day. The data were compatible with high maintenance rates (0.01 to 0.02 h-1) more often associated with bacterial growth in liquid suspension than in soil. Bacterial C:N ratio appeared to be quite low (2.8), and there was no strong evidence that C:N was variable over the 64-h period considered. This paper presents evidence that uptake of NH4+ is limited by diffusion, and that use of different carbon sources is sequential. The need for more information on organic waste production is also discussed. The modeling approach employed should be useful for interpreting data from the chloroform fumigation technique for soil biomass.