title: Development of a highly specific and productive process for n-caproic acid production: applying lessons from methanogenic microbiomes.
abstract: High productivity and specificity in anaerobic digesters arise because complex microbiomes organize into a metabolic cascade to maximize energy recovery and to utilize the advantage that the gaseous end product methane freely bubbles out of the system. These lessons were applied to ascertain whether a reactor microbiome could be shaped to produce a different end product. The liquid product n-caproic acid was chosen, which is a 6-carbon-chain carboxylic acid that is valuable and that has a relatively low maximum solubility concentration for product recovery. Acetoclastic methanogenesis was inhibited by pH control and a route was provided for n-caproic acid extraction by implementing selective, in-line recovery. Next, ethanol was supplemented to promote chain elongation, which is a pathway in which short-chain carboxylic acids are elongated sequentially into medium-chain carboxylic acids with two-carbon units derived from ethanol. The reactor microbiome developed accordingly with the terminal process catalyzed by chain-elongating bacteria. As a result, n-caproic acid production rates increased to levels comparable to anaerobic digestion systems for solid waste treatment.
authors.affiliation: Department of Biological and Environmental Engineering, 214 Riley-Robb Hall, Cornell University, Ithaca, NY 14853, USA E-mail: la249@cornell.edu; Current address: Department of Plant-Microbe Interactions, Max Planck Institute for Plant Research, Carl-von-Linné Weg 10, 50829 Cologne, Germany.
authors.forename: M T
authors.initials: MT
authors.lastname: Agler
authors.affiliation: Department of Biological and Environmental Engineering, 214 Riley-Robb Hall, Cornell University, Ithaca, NY 14853, USA E-mail: la249@cornell.edu.
authors.forename: C M
authors.initials: CM
authors.lastname: Spirito
authors.affiliation: Department of Biological and Environmental Engineering, 214 Riley-Robb Hall, Cornell University, Ithaca, NY 14853, USA E-mail: la249@cornell.edu.
authors.forename: J G
authors.initials: JG
authors.lastname: Usack
authors.affiliation: Department of Biological and Environmental Engineering, 214 Riley-Robb Hall, Cornell University, Ithaca, NY 14853, USA E-mail: la249@cornell.edu; Current address: Department of Plant-Microbe Interactions, Max Planck Institute for Plant Research, Carl-von-Linné Weg 10, 50829 Cologne, Germany.
authors.forename: J J
authors.initials: JJ
authors.lastname: Werner
authors.affiliation: Department of Biological and Environmental Engineering, 214 Riley-Robb Hall, Cornell University, Ithaca, NY 14853, USA E-mail: la249@cornell.edu.
authors.forename: L T
authors.initials: LT
authors.lastname: Angenent
mesh_terms: D000693:Anaerobiosis; D019149:Bioreactors / Q000382:microbiology*; D002208:Caproates / Q000378:metabolism*; D012037:Refuse Disposal / Q000379:methods
chemical_list: D002208:Caproates; C037652:hexanoic acid