The Condition 7 was carried out in order to investigate if the proposal of interchanging the type of sugar is enough to alter the metabolic route of the bacterium and, consequently, the composition of the medium with the purpose of minimizing possible inhibition effects of the photo-fermentation medium and, consequently, extending the evolution process of hydrogen with high productivity. The initial composition of DFE supplemented with lactose used as substrate in the photo-fermentation test (Condition 7) was 9.31 g/L of lactose, 14.12 g/L of lactic acid, 0.71 g/L of formic acid, 1.21 g/L of acetic acid, 4.61 g/L of butyric acid and 2.53 g/L of propionic acid. The temperature was 35 ± 3 C and the initial cell concentration was 0.53 gvs/L. The volume of the medium was maintained constant in 700 mL by the replacement with new medium with the same initial composition, except the sugar and the results are presented in Fig. 3.