Bioconversion of C1 gases to produce chemicals has good application prospects. Here, the combination of trace metals optimization using a statistical method with variable-temperature cultivation was used to enhance alcohol synthesis during CO-rich off-gas fermentation by Clostridium carboxidivorans P7. Based on ATCC medium 1754, the optimum concentration of the trace metals was found to be 5-fold Ni2+, Co2+, SeO42+, and WO42+; 3.48-fold Cu2+; 0.55-fold MoO42+; 0.5-fold Zn2+ and (NH4)(2)SO4 center dot FeSO4 center dot 6H(2)O; and additional 44.32 mu M FeCl3 center dot 6H(2)O. The production of alcohol and organic acid changed to 4.40 g/L and 0.50 g/L from 2.16 g/L and 2.37 g/L, respectively, yielding an increase of alcohol-to-product ratio from 47.7% to 89.8%. By fermenting with the optimized medium and timed control of the incubation temperature (37 degrees C [0-24 h]-25 degrees C [24-144 h]), the alcohol titre further increased to 6.97 g/L with 1.67 g/L butanol and 1.33 g/L hexanol, exceeding those previously reported for strain P7. (C) 2017 Elsevier Ltd. All rights reserved.