ABSTRACT
Many factors need to be considered by citric acid producers to obtain the economically most favourable process. Strain breeding is one of these factors. In this chapter we will summarize ways to improve citric acid production genetically. Commercial production of citric acid is performed mainly with Aspergillus niger and to some extent with Candida (or Yarrowia) lipolytica. As the existing fermentation processes usually give high yields, the main objective of strain breeding nowadays is shortening of fermentation time. However, other factors may also be relevant for strain improvement. For example, accumulation of a high concentration of citric acid by A. niger results from quite extreme culture conditions and strain breeding may decrease the sensitivity of the process to these conditions.
