Fig. 4

Bioreactor batch fermentation profiles of the two strains for butyl butyrate production at different pH values. The strains were seeded at an inoculation ratio of 1:4 (butyrate-producing strain (EB243ΔadhE2::yciAh): butanol-producing strain (EB243) in modified M9Y medium supplemented with 50 g/L glucose. The system was composed of the fermentation broth and hexadecane as extractant at a volume ratio of 1:1. a Optical density at 600 nm (OD₆₀₀), b glucose consumption, c butyl butyrate produced during the fermentation, and d butyrate and butanol. All parameters were assessed at pH 5.5, 5.8, and 6.0. Butyrate, OD₆₀₀, butanol, butyl butyrate, and glucose were measured every 24 h. Error bars indicate the standard deviations from three biological replicates