Fig 2.

Growth and solvent formation of C. acetobutylicum agr mutants. Wild-type C. acetobutylicum and agr mutants were grown in CBM-S broth. (A) Growth was monitored by following the optical density at 600 nm: wild type (asterisks), agrA mutant (triangles), agrB mutant (circles), agrC mutant (diamonds). (B) After 72 h, culture supernatant samples were taken and analyzed for the produced acids (acetate, checks; butyrate, lines) and solvents (butanol, white; acetone, gray; ethanol, black). The values shown are the means ± standard errors of the means of results from six independent experiments. Product concentrations are not significantly different between the wild-type and the mutant strains, except for the difference between butyrate produced by the agrA mutant and the wild type (P = 0.02).