Unorthodox methods for enhancing solvent production in solventogenic Clostridium species
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While production of biofuels from renewable resources is currently receiving increased attention globally, concerns on availability and sustainability of cheap substrates for their production are growing as well. Lignocellulose-derived sugars (LDS) remain underutilized and merit consideration as a key feedstock. Among other obstacles such as low yield and low solvent titer, mitigation of stresses stemming from lignocellulose-derived microbial inhibitory compounds (LDMICs) that severely impair cell growth and solvent production is a major area of research interest. In addition to attempts at developing LDMIC-tolerant strains via metabolic engineering to enhance utilization of LDS, unconventional approaches that elicit different metabolic perturbations in microorganisms to relieve solvent- and LDMIC-mediated stresses have been explored to increase solvent production from LDS. In this review, the impacts of metabolic perturbations including medium supplementation with glycerol; furfural and 5-hydroxymethyl furfural; allopurinol, an inhibitor of xanthine dehydrogenase; calcium (Ca2+) and zinc (Zn2+) ions); and artificial electron carriers, methyl viologen and neutral red, on butanol production are discussed. Although these approaches have brought about considerable increases in butanol production, both from LDS and defined glucose-based media, the modes of action for most of these perturbations have yet to be fully characterized. Better understanding of these mechanisms would likely inform development of LDMIC-tolerant, butanol-overproducing strains, as well as possible combinatorial application of these approaches for enhanced butanol production. Hence, delineating the underlying mechanisms of these perturbations deserves further attention.
KeywordsLignocellulose Butanol Glycerol Allopurinol Calcium carbonate
Salaries and research support were provided in part by State funds appropriated to the Ohio State University, Ohio Agricultural Research and Development Center (OARDC), and the Hatch grant (project no. OHO01333). This research was also supported in part by grants to T.C.E. from the US Department of Transportation (grant DTOS59-07-G-00052) and the Northeast Sun Grant Initiative award/agreement no. 52110-9615.
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Conflict of interest
The authors declare no conflicts of interest.
This article does not contain any studies with human participants or animals performed by any of the authors.
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