Identification, cloning and heterologous expression of active [NiFe]-hydrogenase 2 from Citrobacter sp. SG in Escherichia coli

- We introduce a direct hydrogen assay based on a semiconducting device.
- We identify a Citrobacter sp. strain producing hydrogen under aerobic cultivation.
- Citrobacter sp. contains a type 2 [NiFe]-hydrogenase that is active in vitro.
- The hydrogenase 2 operon allows recombinant hydrogen production in E. coli.
- The enzyme may be useful for biological hydrogen production.