DISSOLVED CARBON-DIOXIDE EFFECTS ON MORPHOLOGY, GROWTH, AND CITRATE PRODUCTION IN ASPERGILLUS-NIGER A60

The effect of increased levels of dissolved carbon dioxide (dCO(3)) on batch cultures of Aspergillus niger A60 was examined by means of cont inuous gassing with inlet gas mixtures containing a range of CO2 conce ntrations (0, 1, 3, 5, 7.5, 12, 15% v/v). In addition to assessing the effect of elevated elevated dCO(2) on the process in terms of biomass , product (citrate) formation, and substrate consumption, the impact o n the morphology of the fungus was quantitatively assessed by use of a n image analysis system which was used to measure critical morphologic al parameters such as main hyphal length, mean branch length, and the value of the hyphal growth unit. In processes where the inlet gas stre am contained more than 3% CO2, raised CO2 was associated with decrease d biomass and citrate concentrations, decreased substrate consumption, and changes in yield factors. Morphologically, elevated dCO(2) was as sociated with changes in the value of the critical morphological param eters. This effect became more pronounced as the rime of exposure incr eased. Some possible mechanisms for these results are discussed includ ing the possibility of specific effects on critical enzymes in the cit rate synthetic pathway. (C) 1997 by Elsevier Science Inc.