FIG 2.

In vivo reduction of CO₂ by C. acetobutylicum expressing the CODH/ACS complex. CO is a product of CO₂ reduction, as shown by ¹³C-tracing. C. acetobutylicum expressing the CODH/ACS enzyme complex was grown on glucose in defined medium in sealed serum bottles with 10 lb/in² CO₂ and H₂ (20/80) in the headspace. (A) CO concentration in headspace at 0, 12, and 24 h. Empty vector (EV) control never produced any CO. (B) Percentage of ¹³CO in CO after addition of [¹³C]bicarbonate to actively growing and CO-producing cells. (C) GC-MS spectra of headspace gas samples from C. acetobutylicum expressing CODH/ACS (left) and empty vector control (right). The CODH/ACS strain exhibits a CO peak at 0.98 min after 20 h. Gas analysis from the control strain (EV) shows only the N₂ peak at 0.9 min but no CO peak. (D) Schematic depicting the interaction of ferredoxin with the hydrogenase and the CODH. (E) C. acetobutylicum expressing CODH/ACS enzyme grown on glucose in defined medium in sealed serum bottles with 20% CO₂ and H₂ or He balance in the headspace (10 lb/in²). More CO is produced in the presence of hydrogen than in the absence of hydrogen. The amount of CO (in nanomoles) produced per culture after 24 h was statistically significant (**, P < 0.005) compared to that produced in the presence of He. Error bars indicate the standard error of at least two biological replicates, and statistical significance was tested with a two-sample t test.