Analysis of polyhydroxybutyrate flux limitations by systematic genetic and metabolic perturbations

Keith E J Tyo, Curt R. Fischer, Fritz Simeon, Gregory Stephanopoulos*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

46 Scopus citations


Poly-3-hydroxybutyrate (PHB) titers in Escherichia coli have benefited from 10+ years of metabolic engineering. In the majority of studies, PHB content, expressed as percent PHB (dry cell weight), is increased, although this increase can be explained by decreases in growth rate or increases in PHB flux. In this study, growth rate and PHB flux were quantified directly in response to systematic manipulation of (1) gene expression in the product-forming pathway and (2) growth rates in a nitrogen-limited chemostat. Gene expression manipulation revealed acetoacetyl-CoA reductase (phaB) limits flux to PHB, although overexpression of the entire pathway pushed the flux even higher. These increases in PHB flux are accompanied by decreases in growth rate, which can be explained by carbon diversion, rather than toxic effects of the PHB pathway. In chemostats, PHB flux was insensitive to growth rate. These results imply that PHB flux is primarily controlled by the expression levels of the product forming pathway and not by the availability of precursors. These results confirm prior in vitro measurements and metabolic models and show expression level is a major affecter of PHB flux.

Original languageEnglish (US)
Pages (from-to)187-195
Number of pages9
JournalMetabolic Engineering
Issue number3
StatePublished - May 2010


  • Chemostat
  • Flux control
  • Overexpression
  • PHB
  • Poly-3-hydroxybutyrate

ASJC Scopus subject areas

  • Biotechnology
  • Bioengineering
  • Applied Microbiology and Biotechnology


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