TABLE 2.

Hydrogenase activity in wild-type Salmonella serovar Typhimurium or in hydrogenase mutant strains containing a single uptake enzyme

Strain or genotype	Enzyme(s)	Hydrogenase activity (nmol H2/min/109 cells)a
		H2 evolution	H2 uptake with endogenous acceptorsb	H2 uptake with oxygenc
Wild type	Hya, Hyb, Hyd	<0.02d	27 ± 9	47 ± 8
Δhyb Δhyd	Hya	<0.02d	5.2 ± 2.8	18 ± 4
Δhyb Δhya	Hyd	18 ± 8	ND	5.2 ± 1.5
Δhyd Δhya	Hyb	17 ± 7	ND	14 ± 5
Triple mutant	None	14 ± 6	ND	<0.02d

^aCells were grown overnight anaerobically in bottles containing CR-HYD media with 0.4% glucose and 20 mM sodium formate. Results are the means ± standard deviations for at least three independent experiments.

^bH₂ uptake was first assayed anaerobically with overnight cultures in media, with no exogenous electron acceptor added as indicated. In this case (i.e., anaerobic assays), H₂ uptake could not be assessed (ND, not done) for three of the strains due to ample H₂ evolution.

^cH₂ uptake was assayed with low levels (final concentration, 45 to 85 μM) of oxygen added via syringe into the amperometric chamber from a 100% O₂-saturated solution. H₂ (75.4 nmol) from a 100% saturated solution in phosphate-buffered saline was injected into the chamber to initiate H₂ uptake assays.

^dThis level was deemed to be the minimum detectable level by the amperometric assay. H₂ evolution was assayed anaerobically, sometimes after a lag (see the text).