What They Saw
They grew A. vinelandii CA in Burk broth but with mannose instead of glucose or sucrose, and either hydrogen or argon in the atmosphere (along with nitrogen and oxygen). They used 14C mannose to observe its uptake via the radioactivity of the isotope.
The increase in radioactivity from mannose activity was a lot higher in cells given hydrogen than those without, up to 5-fold.
They tried inhibiting respiration to see if that was related to this effect, and found that usually by inhibiting respiration, they could inhibit the increased mannose uptake, so it seems to be respiration-dependent rather than some sort of regulatory effect.
So this seems to be another of hydrogen's possible roles in the energy metabolism of Azotobacter.