Enhanced productions of poly-3-hydroxybutyrate and glycogen in cyanobacterium Synechocystis sp. PCC 6803 by disrupting related biosynthetic pathways under phosphorus deprivation.

Under normal growth (NORMAL) condition with adequate supply of phosphorus and nitrogen, the wellstudied cyanobacterium Synechocystis wild type (WT) produced a high biomass level but subtle contents of the two biopolymers: poly-3-hydroxybutyrate (PHB) and glycogen. In contrast, under nitrogen deprivation, growth of WT was terminated, while the accumulations of PHB and glycogen were increased. Thus, a strain and a cultivation strategy that simultaneously allows both biomass production and the increased storages of the two biopolymers are desirable. Here, under phosphorus deprivation (-P), WT grew and still produced biomass at 850 mg/l (accounting for 62% of the biomass level obtained under NORMAL cultivation) with slightly increased contents of PHB and glycogen at 0.5% and 5.5% (w/w DW), respectively. Under -P, the △G mutant with the inactivated glycogen synthesis produced biomass at 751 mg/l and enhanced PHB accumulation to 4.9% (w/w DW), corresponding to PHB production of 36 mg/l. The △HP mutant with the inactivation of both PHB and hydrogen-gas syntheses under -P produced biomass at 713 mg/l and increased glycogen storage to 14.6% (w/w DW), corresponding to glycogen production of 118 mg/l. The significantly reduced levels of both chlorophyll and phycobilisomes (the main photosynthetic protein complex) found in △G and △HP mutants under -P suggested that photosynthetic proteins were degraded into amino acids which might subsequently be used for PHB and glycogen syntheses. The results indicated that the metabolic engineering combined with -P cultivation concurrently allowed cell growth and increased the production of two biopolymers in the studied Synechocystis. [ABSTRACT FROM AUTHOR]