TABLE 1.

Hydrogen oxidation activities with oxygen and methylene blue^a

Strain (electron acceptor)	H2 uptake activity (nmol/min/109 cells)
H. pylori 43504 (O2)	37 ± 2
H. pylori 26695 (O2)	33 ± 4
H. hepaticus 51449 (O2)	3.2 ± 0.2
H. pylori 26695 (MB, aerobic)	23 ± 4
H. pylori 26695 (MB, anaerobic)	176 ± 15
H. hepaticus 51449 (MB, aerobic)	3.9 ± 0.5
H. hepaticus 51449 (MB, anaerobic)	25 ± 2

^aHydrogen concentrations were determined directly amperometrically as described previously (12, 14) on 0.5-ml cell aliquots (in argon-sparged PBS containing between 1.2 × 10⁹ and 3.2 × 10⁹ cells per ml) added to a 2.8-ml-volume amperometric chamber equipped to monitor both H₂ and O₂ levels. Live intact cells were used for oxygen-dependent measurements, and Triton X-100-permeabilized cells (19) were used for the methylene blue (MB)-dependent measurements. For permeabilization, 2 ml of cell suspension received 10 μl of 10% Triton X-100 solution, and the suspension-detergent mixture was incubated at room temperature (but in 100% argon atmosphere) for 20 min before assay. Cell numbers were determined by taking the average from direct counting (by microscopy) of 10 replicate fields on slides. The oxygen level for the aerobic assays was approximately 20 μM, and the anaerobic assays contained 50 μM (freshly prepared in argon-sparged PBS) sodium dithionite. Methylene blue was added to saturation of activity, which was up to 250 μM. Other details of procedures are as described previously (12). The data are the means ± standard deviations for four or five independent replicate samples.