title: Enhancing photo-catalytic production of organic acids in the cyanobacterium Synechocystis sp. PCC 6803 ΔglgC, a strain incapable of glycogen storage.
abstract: A key objective in microbial biofuels strain development is to maximize carbon flux to target products while minimizing cell biomass accumulation, such that ideally the algae and bacteria would operate in a photo-catalytic state. A brief period of such a physiological state has recently been demonstrated in the cyanobacterium Synechocystis sp. PCC 6803 ΔglgC strain incapable of glycogen storage. When deprived of nitrogen, the ΔglgC excretes the organic acids alpha-ketoglutarate and pyruvate for a number of days without increasing cell biomass. This study examines the relationship between the growth state and the photo-catalytic state, and characterizes the metabolic adaptability of the photo-catalytic state to increasing light intensity. It is found that the culture can transition naturally from the growth state into the photo-catalytic state when provided with limited nitrogen supply during the growth phase. Photosynthetic capacity and pigments are lost over time in the photo-catalytic state. Reversal to growth state is observed with re-addition of nitrogen nutrient, accompanied by restoration of photosynthetic capacity and pigment levels in the cells. While the overall productivity increased under high light conditions, the ratio of alpha-ketoglutarate/pyruvate is altered, suggesting that carbon partition between the two products is adaptable to environmental conditions.
authors.affiliation: Biosciences Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO, 80401, USA.
authors.forename: Damian
authors.initials: D
authors.lastname: Carrieri
authors.forename: Charlie
authors.initials: C
authors.lastname: Broadbent
authors.forename: David
authors.initials: D
authors.lastname: Carruth
authors.forename: Troy
authors.initials: T
authors.lastname: Paddock
authors.forename: Justin
authors.initials: J
authors.lastname: Ungerer
authors.forename: Pin-Ching
authors.initials: PC
authors.lastname: Maness
authors.forename: Maria
authors.initials: M
authors.lastname: Ghirardi
authors.forename: Jianping
authors.initials: J
authors.lastname: Yu
mesh_terms: D006003:Glycogen / Q000378:metabolism*; D007656:Ketoglutaric Acids / Q000378:metabolism*; D008027:Light; D053858:Metabolic Networks and Pathways; D009584:Nitrogen / Q000378:metabolism; D019289:Pyruvic Acid / Q000378:metabolism*; D046939:Synechocystis / Q000254:growth & development* / Q000378:metabolism*
chemical_list: D007656:Ketoglutaric Acids; D019289:Pyruvic Acid; D006003:Glycogen; D009584:Nitrogen