EFFECTS OF ELEVATED DISSOLVED CO2 LEVELS ON BATCH AND CONTINUOUS CULTURES OF ASPERGILLUS-NIGER A60 - AN EVALUATION OF EXPERIMENTAL METHODS

The effects of elevated levels of dissolved carbon dioxide (dCO(2)), p roduced by gassing with CO2-enriched gas mixtures, upon an industrial strain of Aspergillus niger (strain A60) producing citrate and glucona te were quantitatively assessed. Particular attention was paid to the reliability and accuracy of the steam-sterilizable dCO(2) probe, espec ially in the presence of high concentrations of potentially interferin g acidic species. The response of the organism to elevated dCO(2) leve ls was assessed by using both batch and chemostat cultures, and the se nsitivity of the organism in different growth phases (lag, exponential , and stationary) was examined, Chemostat cultures showed markedly les s inhibition (in terms of biomass and organic acid synthesis) than did batch cultures. Studies in batch culture indicated that lag-phase cul tures were especially sensitive to elevated dCO(2) levels. Overall, th e results of this study indicate that previous experimental methods us ed to examine dCO(2) effects in submerged cultures (continuous CO2-enr iched gassing of batch cultures from time zero) have been inappropriat e and have led to systematic overestimation of the inhibitory effects of dCO(2) on mycelial organisms.