Nitrogen sources impact hydrogen production by Escherichia coli using cheese whey as substrate

• Type of nitrogen source affects hydrogen production by E. coli.
• Ammonium salts have no effect on hydrogen production.
• Yeast extract and tryptone positively affect hydrogen production.

The impact of nitrogen source on hydrogen production by Escherichia coli WDHL (ΔhycAΔlacI) strain using cheese whey as a substrate was evaluated. To improve the assimilation of complex proteins such as lactalbumin, we assessed treatment with a protease. Also, five external nitrogen sources were tested: NH4Cl, (NH4)2SO4, urea, yeast extract, and tryptone. The treatments in 120 mL serological bottles with pancreatin 1000 mg/L produced 1.75-fold more hydrogen than the cultures without pancreatin. In the bottle cultures supplemented with yeast extract or tryptone 5 g/L, hydrogen production increased up to 3.2- and 3.5-fold, respectively, whereas inorganic salts and urea had no statistical difference with respect to the control cultures. In 1-L bioreactors, the use of tryptone improved 2.1-fold hydrogen production. Tryptone or yeast extract enable the total consumption of lactose in 40 h, whereas in the control assay the lactose was not completely consumed. Our results demonstrate that it is necessary to select an adequate nitrogen source, which allows both carbon source consumption and high hydrogen production.