Targeted Repression of Essential Genes To Arrest Growth and Increase Carbon Partitioning and Biofuel Titers in Cyanobacteria

ACS Synth Biol. 2018 Jul 20;7(7):1669-1675. doi: 10.1021/acssynbio.8b00056. Epub 2018 Jun 8.

Abstract

Photoautotrophic production of fuels and chemicals by cyanobacteria typically gives lower volumetric productivities and titers than heterotrophic production. Cyanobacteria cultures become light limited above an optimal cell density, so that this substrate is not supplied to all cells sufficiently. Here, we investigate genetic strategies for a two-phase cultivation, where biofuel-producing Synechocystis cultures are limited to an optimal cell density through inducible CRISPR interference (CRISPRi) repression of cell growth. Fixed CO2 is diverted to ethanol or n-butanol. Among the most successful strategies was partial repression of citrate synthase gltA. Strong repression (>90%) of gltA at low culture densities increased carbon partitioning to n-butanol 5-fold relative to a nonrepression strain, but sacrificed volumetric productivity due to severe growth restriction. CO2 fixation continued for at least 3 days after growth was arrested. By targeting sgRNAs to different regions of the gltA gene, we could modulate GltA expression and carbon partitioning between growth and product to increase both specific and volumetric productivity. These growth arrest strategies can be useful for improving performance of other photoautotrophic processes.

Keywords: CRISPRi; cyanobacteria; dynamic metabolic engineering; growth-arrest; light availability.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biofuels*
  • Carbon / metabolism*
  • Clustered Regularly Interspaced Short Palindromic Repeats / genetics
  • Cyanobacteria / genetics
  • Cyanobacteria / metabolism*
  • Cyanobacteria / radiation effects
  • Light*
  • Metabolic Engineering

Substances

  • Biofuels
  • Carbon