Conflicting reports have also been cited regarding the
effects of nitrogen and phosphate limitation. According to Shu
and Johnson (92, 93), phosphate needs not be limiting for citric
acid production; however, when metal levels are not limiting,
additional phosphate leads to secondary reactions and promotes
biomass growth (76, 79, 80). However, Kubicek and Rohr (40)
demonstrated that citric acid accumulated when phosphate was
limiting, even when nitrogen was not. Instead, Kristiansen and
Sinclair (37), using a continuous culture, came to the
conclusion that the limitation by nitrogen is essential for the
production of citric acid.