Isolation and screening of carboxydotrophs isolated from composts and their potential for butanol synthesis

Abstract

Carboxydotrophs are known for their ability to convert carbon monoxide (CO) to butanol through fermentation. Such a platform offers a promising alternative approach to biofuel production from synthesis gas feedstocks. In this study, carboxydotrophs were isolated from various manure compost. Out of 500 isolates, only 11 carboxydotrophs (7 mesophiles and 4 thermophiles) were found to utilize CO as the sole source of carbon and energy. To assess the biochemical basis for their ability to produce biofuel (butanol), the level of activities of CO dehydrogenase (CODH), hydrogenase and butanol dehydrogenase (BDH) enzymes for these isolates against the known carboxydotroph, Butyribacterium methylotrophicum was assessed. All isolates showed evidence of enzyme activities (0.16–2.20 μmol min⁻¹), with the majority exhibiting higher activities compared with the known carboxydotroph, B. methylotrophicum (0.33–0.71 μmol min⁻¹). The level of activities for CODH and BDH ranged from 0.163–3.59 μmol min⁻¹ and 0.19–2.2 μmol min⁻¹, respectively. Three isolates (M7-1, T2-22, and T3-14) demonstrated enzymatic activity three to seven times higher than B. methylotrophicum. Of these, T2-22 exhibited the highest BDH activity and shows great promise in the conversion of toxic CO into butanol more so than other carboxytotrophs known thus far. This study revealed some biochemical basis for butanol production from CO by carboxydotrophs. However, more research is needed to discover a direct biological route for butanol production from CO to strengthen their potential for synthesis gas bioprocessing. Follow-up work will focus on whole-genome sequencing of the promising isolate T2-22 to provide system-level insights into how carboxydotrophs utilize and regulate their molecular machineries for butanol production.

Keywords:

• carboxydotrophs
• carbon monoxide dehydrogenase
• butanol dehydrogenase
• biobutanol
• syngas

Acknowledgements

We thank the University of Michigan Energy Institute for financial support. We also thank Kurt Cafini, Linda Grimm, Bob Quattro, Kathy Leach and Michael Skorupta of the Department of Natural Sciences for their assistance with configuring the gas system setup for the experiments.