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

Janine Kaewbai-ngam^a,b, Tanakarn Monshupanee^a,*

 
ABSTRACT:     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.

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* Corresponding author, E-mail: tanakarn.m@chula.ac.th

Received 16 Jun 2023, Accepted 14 Dec 2023