Περίληψη:
Acetaldehyde is a valuable product of microbial biosynthesis, which can be used by the chemical industry as the entry point for production of various commodity chemicals. In ethanologenic microorganisms, like yeast or the bacterium Zymomonas mobilis, this compound is the immediate metabolic precursor of ethanol. In aerobic cultures of Z. mobilis, it accumulates as a volatile, inhibitory byproduct, due to the withdrawal of reducing equivalents from the alcohol dehydrogenase reaction by respiration. The active respiratory chain of Z. mobilis with its low energy-coupling efficiency is well-suited for regeneration of NAD+ under conditions when acetaldehyde, but not ethanol, is the desired catabolic product. In the present work, we sought to improve the capacity Z. mobilis to synthesize acetaldehyde, based on predictions of a stoichiometric model of its central metabolism developed herein. According to the model analysis, the main objectives in the course of engineering acetaldehyde producer strains were determined to be: (i) reducing ethanol synthesis via reducing the activity of alcohol dehydrogenase (ADH), and (ii) enhancing the respiratory capacity, either by overexpression of the respiratory NADH dehydrogenase (NDH), or by mutation of other components of respiratory metabolism. Several mutants with elevated respiration rate, decreased alcohol dehydrogenase activity, or a combination of both, were obtained. They were extensively characterized by determining their growth rates, product yields, oxygen consumption rates, ADH, and NDH activities, transcription levels of key catabolic genes, as well as concentrations of central metabolites under aerobic culture conditions. Two mutant strains were selected, with acetaldehyde yield close to 70% of the theoretical maximum value, almost twice the previously published yield for Z. mobilis. These strains can serve as a basis for further development of industrial acetaldehyde producers. © Copyright © 2019 Kalnenieks, Balodite, Strähler, Strazdina, Rex, Pentjuss, Fuchino, Bruheim, Rutkis, Pappas, Poole, Sawodny and Bettenbrock.
Συγγραφείς:
Kalnenieks, U.
Balodite, E.
Strähler, S.
Strazdina, I.
Rex, J.
Pentjuss, A.
Fuchino, K.
Bruheim, P.
Rutkis, R.
Pappas, K.M.
Poole, R.K.
Sawodny, O.
Bettenbrock, K.
Λέξεις-κλειδιά:
acetaldehyde; alcohol dehydrogenase; genomic DNA; messenger RNA; reduced nicotinamide adenine dinucleotide dehydrogenase, aerobic metabolism; Article; bacterial growth; bacterial strain; biomass; biosynthesis; breathing rate; carbon nuclear magnetic resonance; controlled study; electron transport; enzyme activity; Escherichia coli; gas chromatography; gene expression; gene mutation; gene overexpression; glucose metabolism; ion chromatography; liquid chromatography-mass spectrometry; mass spectrometry; metabolic engineering; metabolite; metabolomics; nonhuman; nucleotide sequence; oxygen consumption; plasmid; protein synthesis; real time polymerase chain reaction; respiratory chain; stoichiometry; Zymomonas mobilis
