A bubble column continuous fermentation system for trimethylamine conversion by Aminobacter aminovorans

Abstract

The effect of changing dilution rate on Aminobacter aminovorans grown in chemostat cultures was studied. The microorganism was cultivated at dilution rates between 0.015–0.12 h −1. The biomass level remained fairly constant up to values of D around 0.07 h −1. At higher dilution rates, cell density began to decrease which indicated that the growth rate was leading to a wash-out of the culture. The maximum cell production rate (0.08 g l −1 h −1) was obtained in the region between 0.09 and 0.11 h −1 corresponding to a maximum conversion of the carbon into cell mass (65%). The highest rate of trimethylamine consumption was 1.79 m m h −1 occurring at the D = 0.062 h −1. The biomass productivity profile follows a classical pattern suggesting a culture wash-out near 0.15 h −1. The flux of carbon from trimethylamine toward cell synthesis and carbon dioxide production was expressed in terms of carbon recovery. Data show that the flux of carbon to cells and CO 2 drops from 100% to values between 66.4–74.1% in the region D = 0.027 h −1 to D = 0.07 h −1. The decrease in carbon recovery suggested a shift toward a different growth limitation; however, in the maximum dilution rate region (0.1 h −1) and above, the levels of carbon recovery increased to values closer to carbon limitation. The data is consistent with an industrial trimethylamine transformation using A. aminovorans particularly when the lower growth rates (0.035 h −1 or below) are used.