This represents a yield of 0.78 mol mol−1 on glucose and a productivity of 0.27 g liter−1 h−1. Furthermore, they investigated the effect of the nitrogen source, including, among others, peptone and ammonium sulfate, and reported final titers of 32.6 g liter−1 and 30.4 g liter−1, respectively, after 7 days of fermentation from 100 g liter−1 glucose. The same strain was used in the late 1980s and early 1990s for further investigation of the metabolism toward malic acid production. It was reported that de novo enzyme synthesis during nitrogen starvation resulted in an increase of malate synthesis, as malate dehydrogenase activity increased and fumarase activity changed only slightly