(746c) Isobutanol Pathway As a Metabolic Sink for the Glgc Mutant of Synechococcus Elongatus PCC 7942

Glycogen synthesis catalyzed by the glucose-1-phosphate adenylyltransferase (glgC) represents a major carbon storage route in cyanobacteria which could divert significant portion of the carbon flux. Here we present the construction of glgC knock-out in the S. elongatus PCC7942 isobutanol producer and the analysis of its effects on carbon distribution. Deletion of glgC increased the normalized isobutanol productivity under constant light during the log-phase. Interestingly, whereas wild type ΔglgC suffered severe growth inhibition and photo-bleaching, overexpression of isobutanol synthesis pathway in the ΔglgC strain prolonged cell growth and led to higher chlorophyll content. In addition, the growth rescue effect caused by isobutanol pathway activity is positively correlated to the capacity of isobutanol production.  Bashed on the carbon 14 incorporation analysis, while wild type ΔglgC mutant displayed significant amount of carbon fixation loss due to inability of glycogen synthesis, overexpression of the isobutanol pathway in the ΔglgC strain restored the total carbon fixation rate back to the level of wild type. In addition, deletion of glgC successfully channeled more carbon flux into the isobutanol pathway. This high percentage suggests that cyanobacteria based biofuel productivity may be limited by its intrinsic carbon fixation capacity.