Biochemical basis for carbon monoxide tolerance and butanol production by Butyribacterium methylotrophicum

The biochemical mechanisms for growth tolerance to a 100% CO headspace in c ultures, and butanol plus ethanol production from CO by Butyribacterium met hylotrophicum were assessed in the wild-type and CO-adapted strains. The CO -adapted strain grew on glucose or CO under a 100% CO headspace, whereas, t he growth of the wild-type strain was severely inhibited by 100% CO. The CO -adapted strain, unlike the wildtype, also produced butyrate, from either p yruvate or CO. The CO-adapted strain was a metabolic mutant having higher l evels of ferredoxin-NAD oxidoreductase activity, which was not inhibited by NADH. Consequently, only the CO-adapted strain can grow on CO because CO o xidation generates reduced ferredoxin which, via the mutated ferredoxin-NAD reductase activity, forms reduced NADH required for catabolism. When the C O-adapted strain was grown at pH 6.0 it produced butanol (0.33 g/l) and eth anol (0.5 g/l) from CO and the cells contained the following NAD-linked enz yme activities (mu mol min(-1) mg protein(-1)): butyraldehyde dehydrogenase (227), butanol dehydrogenase (686), acetaldehyde dehydrogenase (82) and et hanol dehydrogenase (129).