Metabolic Characteristics of Citric Acid Synthesis by the Fungus Aspergillus niger

The article discusses recent advances in the study of the metabolism of Aspergillus niger, a producer of citric acid, and some of its characteristics that may be responsible for the overproduction of citric acid. The paper is designed so that the entire process of citrate biosynthesis, from the absorption of glucose from a nutrient medium to the extraction of citric acid from cells, is divided into stages that are critical for the yield of the desired product. This arrangement of the material makes it possible to show the main regulatory steps in the chain of citrate synthesis. Influencing these steps enables regulation of the biosynthesis of citric acid at the level of cellular metabolism. This eventually opens promising avenues in the improvement of producing strains by means of genetic engineering. The paper also reviews the influence of some fermentation conditions (medium components, additives, and technological parameters) on metabolic processes in producing cells, which is important for an integral understanding of both biosynthesis process at the cellular level and fermentation technology.