FIG 6.

Impact of added Ni on CO production by C. acetobutylicum expressing the CODH/ACS complex without or with coexpression of the Ni-inserting CooC protein. (A) CO concentration was measured in the headspace for concentrated C. acetobutylicum expressing the CODH/ACS complex alone (blue circles/line) or with the accessory protein CooC (orange squares/line) after 24 h of growth in defined medium with various amounts of Ni. (B) Total CO produced in the absence of nickel for the CODH/ACS-expressing strain (blue) and the CODH/ACS–CooC-expressing strain (orange). There is a significant difference at the 90% confidence level between the two strains (*, P < 0.1; n = 4), indicating that the accessory protein can facilitate nickel insertion into the active site in the presence of trace levels (residual) of Ni. Error bars indicate the standard error of at least two biological replicates.