Under dark, anaerobic conditions in the presence of sufficient nickel,
Rhodospirillum rubrum grows with a doubling time of under 5 h by coup
ling the oxidation of CO to the reduction of H+ to H-2. CO-dependent g
rowth of R. rubrum UR294, bearing a kanamycin resistance cassette in c
ooC, depends on a medium nickel level ninefold higher than that requir
ed for optimal growth of coo(+) strains.