FIG. 4.
Hydrogenase gene expression in the presence of various NiCl2 concentrations. The R. eutropha strains HF459 (HoxN−; black bars) and HF375 (HoxN− HoxJ−; white bars), each containing the plasmid-based Φ(hoxK′-′lacZ) fusion pGE301, were grown in FGN medium containing 10 μM nitrilotriacetic acid at the nonpermissive temperature of 37°C until they reached an OD436 of 7. At time zero the cells were shifted to 30°C and 10% (vol/vol) H2 (+H2) or 10% (vol/vol) N2 (−H2) was added. After further incubation for 5 h the cells were collected, and the β-galactosidase activity was determined.