Citric acid production

Citric acid is a commodity chemical produced and consumed throughout The World. It is used mainly in the food and beverage industry, primarily as an acidulant. Although it is one of the oldest industrial fermentations, its World production is still in rapid increasing. Global production of citric acid in 2007 was over 1.6 million tones. Biochemistry of citric acid fermentation, various microbial strains, as well as various substrates, technological processes and product recovery are presented. World production and economics aspects of this strategically product of bulk biotechnology are discussed.

The succinoxidase system in Aspergillus niger

The succinoxidase system of Aspergillus niger differs from that of avian and mammalian tissues in its greater lability during preparation and storage but is similar in its sensitivity to malonate, cyanide, azide, and B.A.L., its association with cell particles, and its single pH optimum at pH 7.3. The system is not inhibited by arsenite in concentrations up to 0.01 M.

Growth energetics and metabolic fluxes in continuous cultures of Penicillium chrysogenum

Continuous cultures of the penicillin producing fungus Penicillium chrysogenum have been analyzed with respect to the macromolecular composition of the mycelium. All cultivations were carried out using a chemically defined medium with glucose as the growth limiting component. Biomass was harvested at steady state and analyzed for proteins, lipids, RNA, DNA, and carbohydrates. Carbohydrates present in the cell wall, i.e., glucans and chitin, and carbohydrates serving as storage materials, i.e., glycogen, were measured. It was observed that the levels of DNA and lipids are relative constant, whereas the proteins and stable RNA levels increase with the specific growth rate and the total amount of carbohydrates decreases with the specific growth rate. Glycogen is only present in small amounts, decreasing with the specific growth rate. As an average the measured macromolecules account for 77 +/- 2% (w/w) of the biomass. On the basis of estimations of the metabolic costs for biosynthesis and polymerization of the different macromolecules the total ATP and NADPH requirements for cell biosynthesis from glucose and inorganic salts, i.e., YxATP,growth and YxNADPH, have been quantified. The biosynthesis of 1 g biomass was calculated to require 39.9 mmol of ATP and 7.5 mmol of NADPH when cytosolic acetyl-CoA is formed from citrate by citrate lyase and oxaloacetate is recycled back into the TCA cycle. Other pathways of acetyl-CoA biosynthesis have been considered. The calculations show that the different biosynthetic routes for generating cytosolic acetyl-CoA have a significant influence on the theoretical value of ATP and NADPH requirements for cell biosynthesis. Combining a detailed stoichiometric model for growth and product formation of P. chrysogenum with experimental data on the macromolecular composition of P. chrysogenum and precise measurements of substrate uptake and product formation the intracellular flux distribution was calculated for different cultivation conditions.