Abstract
An in-situ, steam-sterilizable capacitance probe was used to follow the biomass concentration on-line, in bioreactors from 20 to 2000 l total volume. Microbial cultures of Saccharomyces cerevisiae, Pichia pastoris and Streptomyces virginiae were grown in batch and fed-batch culture in both defined and complex media in order to demonstrate the wide dynamic operating range of the instrument. A linear correlation was found between the on-line capacitance measurement and the off-line measurements (optical density, OD 620; packed mycelial volume, PMV; biomass concentration X, and colony forming units, CFU ml −1) for biomass concentrations (dry cell weight) up to 30 g l −1 ( St. virginiae), 106 g l −1 ( S. cerevisiae) and 89 g l −1 ( P. pastoris). The on-line capacitance measurement was slightly influenced by variations in agitation speed and strong extraneous radio frequencies. A specific capacitance constant ( C s) was defined for all microbial cells which was dependent on cell viability and cell size. The C s was easy to calculate using the on-line capacitance measurement and an off-line estimation of biomass concentration. The Biomass Monitor proved suitable for precise on-line monitoring of both homogeneous (uni-cellular) and heterogeneous (mycelial) cultures in bioreactors.
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