Engineering Synechococcus elongatus PCC 7942 for Continuous Growth under Diurnal Conditions

Abstract

Synechococcus elongatus strain PCC 7942 strictly depends upon the generation of photosynthetically derived energy for growth and is incapable of biomass increase in the absence of light energy. Obligate phototrophs' core metabolism is very similar to that of heterotrophic counterparts exhibiting diverse trophic behavior. Most characterized cyanobacterial species are obligate photoautotrophs under examined conditions. Here we determine that sugar transporter systems are the necessary genetic factors in order for a model cyanobacterium, Synechococcus elongatus PCC 7942, to grow continuously under diurnal (light/dark) conditions using saccharides such as glucose, xylose, and sucrose. While the universal causes of obligate photoautotrophy may be diverse, installing sugar transporters provides new insight into the mode of obligate photoautotrophy for cyanobacteria. Moreover, cyanobacterial chemical production has gained increased attention. However, this obligate phototroph is incapable of product formation in the absence of light. Thus, converting an obligate photoautotroph to a heterotroph is desirable for more efficient, economical, and controllable production systems.

Controlling the Cyanobacterial Clock by Synthetically Rewiring Metabolism

“…Although S. elongatus is a natural autotroph, using photosynthesis to fix inorganic carbon, it can be modified to metabolize sugar supplied in the culture medium by transgenically expressing the galP sugar symporter gene from Escherichia coli (McEwen et al, 2013) (Figure 1A). …”

Engineering cyanobacteria as photosynthetic feedstock factories

“…For example, application of osmotic stress to sucrose transporter-bearing cyanobacteria greatly increases sugar efflux, and allows for tuning of the amount of fixed carbon that is ultimately exported as sugar (Ducat et al 2012; Du et al 2013; Xuan et al 2013). Many heterologous sugar transporters have been shown to express and localize to the plasma membrane in sufficient quantities for measurable sugar export or import (McEwen et al 2013), an indication that this approach could be expanded for the export of other sugars if strains can be engineered to reverse the chemical gradient across the plasma membrane (i.e. achieve sufficiently high cytosolic levels of target sugars to promote export).…”

Isotopically nonstationary 13C flux analysis of cyanobacterial isobutyraldehyde production

“…To test this, we applied INST-MFA to compare the metabolic network of wild-type S. elongatus with the IBA-producing strain SA590. Because S. elongatus only grows photoautotrophically (McEwen et al, 2013), transient isotope labeling studies and INST-MFA were required for flux determination. The flux analysis revealed a hidden bottleneck at the pyruvate kinase (PK) reaction, which catalyzes the conversion of phosphoenolpyruvate (PEP) to pyruvate, the major carbon precursor of IBA.…”