title: Metabolic response of Clostridium ljungdahlii to oxygen exposure.
abstract: Clostridium ljungdahlii is an important synthesis gas-fermenting bacterium used in the biofuels industry, and a preliminary investigation showed that it has some tolerance to oxygen when cultured in rich mixotrophic medium. Batch cultures not only continue to grow and consume H2, CO, and fructose after 8% O2 exposure, but fermentation product analysis revealed an increase in ethanol concentration and decreased acetate concentration compared to non-oxygen-exposed cultures. In this study, the mechanisms for higher ethanol production and oxygen/reactive oxygen species (ROS) detoxification were identified using a combination of fermentation, transcriptome sequencing (RNA-seq) differential expression, and enzyme activity analyses. The results indicate that the higher ethanol and lower acetate concentrations were due to the carboxylic acid reductase activity of a more highly expressed predicted aldehyde oxidoreductase (CLJU_c24130) and that C. ljungdahlii's primary defense upon oxygen exposure is a predicted rubrerythrin (CLJU_c39340). The metabolic responses of higher ethanol production and oxygen/ROS detoxification were found to be linked by cofactor management and substrate and energy metabolism. This study contributes new insights into the physiology and metabolism of C. ljungdahlii and provides new genetic targets to generate C. ljungdahlii strains that produce more ethanol and are more tolerant to syngas contaminants.
authors.affiliation: Department of Plant and Microbial Biology, North Carolina State University, Raleigh, North Carolina, USA.
authors.forename: Jason M
authors.initials: JM
authors.lastname: Whitham
authors.affiliation: Department of Plant and Microbial Biology, North Carolina State University, Raleigh, North Carolina, USA.
authors.forename: Oscar
authors.initials: O
authors.lastname: Tirado-Acevedo
authors.affiliation: Department of Biological and Agricultural Engineering, North Carolina State University, Raleigh, North Carolina, USA.
authors.forename: Mari S
authors.initials: MS
authors.lastname: Chinn
authors.affiliation: Department of Forest Biomaterials, North Carolina State University, Raleigh, North Carolina, USA.
authors.forename: Joel J
authors.initials: JJ
authors.lastname: Pawlak
authors.affiliation: Department of Plant and Microbial Biology, North Carolina State University, Raleigh, North Carolina, USA amy_grunden@ncsu.edu.
authors.forename: Amy M
authors.initials: AM
authors.lastname: Grunden
mesh_terms: D000085:Acetates / Q000378:metabolism*; D000445:Aldehyde Oxidoreductases / Q000378:metabolism; D001483:Base Sequence; D056804:Biofuels / Q000382:microbiology; D019149:Bioreactors / Q000382:microbiology; D002245:Carbon Dioxide / Q000378:metabolism; D003013:Clostridium / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D004269:DNA, Bacterial / Q000235:genetics; D004734:Energy Metabolism / Q000502:physiology; D000431:Ethanol / Q000378:metabolism*; D005285:Fermentation / Q000502:physiology; D015870:Gene Expression / Q000187:drug effects; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction / Q000187:drug effects; D010088:Oxidoreductases / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism* / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000378:metabolism*; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D000085:Acetates; D056804:Biofuels; D004269:DNA, Bacterial; D017382:Reactive Oxygen Species; D002245:Carbon Dioxide; D000431:Ethanol; D010088:Oxidoreductases; D000445:Aldehyde Oxidoreductases; C019825:carboxylic acid reductase; D010100:Oxygen