(582cd) Analysis of Photomixotrophic Metabolism in Synechocystis Sp. PCC 6803 Via Inverse Tracer-Metabolic Flux Analysis

Analysis of photomixotrophic metabolism in Synechocystis
sp. PCC 6803 via Inverse Tracer-Metabolic Flux Analysis

Cyanobacteria
have gained considerable attention in recent years for their potential
applications in biotechnology. For nearly half a century, extensive research
has been undertaken to characterize photosynthetic metabolism in cyanobacteria.
However, questions still remain about the presence of a complete TCA cycle or
the glyoxylate shunt. We present here a novel method termed Inverse
Tracer-Metabolic Flux Analysis to identify and quantify photosynthetic
metabolism in Synechocystis
sp. PCC 6803. The labeling information of metabolites
under the use of ¹²C-tracers (such as glutamate and glyoxylate) in a
¹³C-based background (NaH¹³CO₃ andU-¹³C₆
glucose), were measured by GC-MS to reveal several metabolic insights. First of
all, we found that TCA pathway, instead of being a cyclic or an incomplete pathway
appeared to be a unique branched structure in Synechocystis,
which
terminated in the production of succinate. Secondly, the in
vivo activity of isocitrate lyase, which involved in the
glyoxylate shunt, was not detected under our experimental conditions. The flux
analysis revealed that glyoxylate can be synthesized through photo-respiration and
can serve as a glycine precursor. Finally, the oxidative pentose phosphate
pathway (OPP pathway) showed a measurable flux under glucose-based mixotrophic
conditions. This study described an economical labeling approach to precisely
characterize functional metabolisms.