Acetylene (10 mL) and a substrate solution consisting of a mixture of electron donors and KNO3 were injected into the flasks through the septa resulting in a final concentration of 0.5 mM glucose, 1.5 mM sodium acetate, 0.75 mM sodium succinate and 1.5 mM KNO3-N. The slurries were incubated 22 h at 15 C with agitation (175 rpm)