Fermentation of oxidized hexose derivatives by Clostridium acetobutylicum

Microbial Cell Factories

Research

Elliot S Gerlach¹  Sanchao Liu¹  Katherine L Germane²  Christian J Sund³  Matthew D Servinsky³ 

[1] Federal Staffing Resources, 2200 Somerville Rd, 21401, Annapolis, MD, USA;Oak Ridge Associated Universities, 4692 Millennium Drive, Suite 101, 21017, Belcamp, Maryland, USA;US Army Research Laboratory, Sensors and Electron Devices Directorate, 2800 Powder Mill Road, 20783, Adelphi, MD, USA;

关键词: Clostridium acetobutylicum;    Fermentation;    Gluconate;    Galacturonate;    Acetate;    Pectin;    Hydrogen;    Carbon dioxide;   

DOI  :  10.1186/s12934-014-0139-7

 received in 2014-05-16, accepted in 2014-09-07,  发布年份 2014

来源: Springer

【 摘 要 】

BackgroundClostridium acetobutylicum fermentations are promising for production of commodity chemicals from heterogeneous biomass due to the wide range of substrates the organism can metabolize. Much work has been done to elucidate the pathways for utilization of aldoses, but little is known about metabolism of more oxidized substrates. Two oxidized hexose derivatives, gluconate and galacturonate, are present in low cost feedstocks, and their metabolism will contribute to overall metabolic output of these substrates.ResultsA complete metabolic network for glucose, gluconate, and galacturonate utilization was generated using online databases, previous studies, genomic context, and experimental data. Gluconate appears to be metabolized via the Entner-Doudoroff pathway, and is likely dehydrated to 2-keto-3-deoxy-gluconate before phosphorylation to 2-keto-3-deoxy-6-P-gluconate. Galacturonate appears to be processed via the Ashwell pathway, converging on a common metabolite for gluconate and galacturonate metabolism, 2-keto-3-deoxygluconate. As expected, increasingly oxidized substrates resulted in increasingly oxidized products with galacturonate fermentations being nearly homoacetic. Calculations of expected ATP and reducing equivalent yields and experimental data suggested galacturonate fermentations were reductant limited. Galacturonate fermentation was incomplete, which was not due solely to product inhibition or the inability to utilize low concentrations of galacturonate. Removal of H2 and CO2 by agitation resulted in faster growth, higher cell densities, formation of relatively more oxidized products, and higher product yields for cultures grown on glucose or gluconate. In contrast, cells grown on galacturonate showed reduced growth rates upon agitation, which was likely due to loss in reductant in the form of H2. The growth advantage seen on agitated glucose or gluconate cultures could not be solely attributed to improved ATP economics, thereby indicating other factors are also important.ConclusionsThe metabolic network presented in this work should facilitate similar reconstructions in other organisms, and provides a further understanding of the pathways involved in metabolism of oxidized feedstocks and carbohydrate mixtures. The nearly homoacetic fermentation during growth on galacturonate indicates further optimization of this and related organisms could provide a route to an effective biologically derived acetic acid production platform. Furthermore, the pathways could be targeted to decrease production of undesirable products during fermentations of heterogeneous biomass.

【 授权许可】

Unknown   
© Servinsky et al.; licensee BioMed Central Ltd. 2014. This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.