title: Unorthodox methods for enhancing solvent production in solventogenic Clostridium species.
abstract: 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 (Ca(2+)) and zinc (Zn(2+)) 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.
authors.affiliation: Department of Animal Sciences, Ohio State Agricultural Research and Development Center (OARDC), The Ohio State University, 305 Gerlaugh Hall, 1680 Madison Avenue, Wooster, OH, 44691, USA.|Renewable Energy Program, Agricultural Technical Institute, The Ohio State University, 1328 Dover Road, Wooster, OH, 44691, USA.
authors.forename: Victor
authors.initials: V
authors.lastname: Ujor
authors.affiliation: Department of Animal Sciences, Ohio State Agricultural Research and Development Center (OARDC), The Ohio State University, 305 Gerlaugh Hall, 1680 Madison Avenue, Wooster, OH, 44691, USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Okonkwo
authors.affiliation: Department of Animal Sciences, Ohio State Agricultural Research and Development Center (OARDC), The Ohio State University, 305 Gerlaugh Hall, 1680 Madison Avenue, Wooster, OH, 44691, USA. ezeji.1@osu.edu.
authors.forename: Thaddeus Chukwuemeka
authors.initials: TC
authors.lastname: Ezeji
mesh_terms: D000440:Butanols / Q000378:metabolism; D003013:Clostridium / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D003470:Culture Media / Q000737:chemistry / Q000378:metabolism*; D007218:Industrial Microbiology / Q000295:instrumentation / Q000379:methods*; D060847:Metabolic Engineering; D012997:Solvents / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000440:Butanols; D003470:Culture Media; D012997:Solvents
keywords: Allopurinol; Butanol; Calcium carbonate; Glycerol; Lignocellulose