Comparison of hydrogen-production capability of four different Enterobacteriaceae strains under growing and non-growing conditions

Non-growing cells can function as whole-cell biocatalysts for hydrogen (H2) production, a process that has recently drawn much attention. In order to evaluate their potential as whole-cell biocatalysts, we compared the H2-production capability of four Enterobacteriaceae strains (Citrobacter amalonaticus Y19, Escherichia coli K-12 MG1655, Escherichia coli DJT135, and Enterobacter aerogenes) under growing and non-growing conditions. We evaluated their H2-production activity at varying temperatures (25–45 °C) and pH conditions (6.0–8.0) using glucose or formate as the carbon source. Under growing conditions with 10 mM glucose as a substrate, E. aerogenes exhibited the highest H2-production activity (17.0 ± 0.2 μmol H2 mg cell−1 h−1) among the four strains, but the final H2 yield was similar (1.7–1.8 mol H2 mol−1 glucose) in all four strains. H2 production in the four strains proceeded through a formate-dependent pathway that involved the formate hydrogen lyase (FHL) complex. Under non-growing conditions with 20 mM formate as a substrate, we obtained high H2-production activities, in the range of 95.5–195.2 μmol H2 mg cell−1 h−1, with E. coli DJT135 exhibiting the highest activity (195.2 μmol H2 mg−1 h−1) at pH 6.0 and 45 °C. In contrast, using glucose as the carbon substrate in non-growing cell experiments greatly reduced the H2-production activity to 6.1–7.7 μmol H2 mg cell−1 h−1. This study indicated that formate is a better substrate than glucose for H2 production by non-growing cells, and that the H2-production performance among the strains did not vary significantly, with the exception of E. coli K-12 MG1655.