Production of glycogen, PHB, biohydrogen, NAD(P)H, and proteins in Synechocystis sp. PCC 6803 disrupted in metabolically linked biosynthetic pathway(s)

Under nitrogen deprivation (-N), cell growth and protein synthesis of Synechocystis sp. PCC 6803 were inhibited but production of glycogen (GL) and poly-3-hydroxybutyrate (PHB) was enhanced, indicating the importance of -N for increasing the production of such bioproducts. Upon transition from N-deprived to N-supplied medium, GL and PHB were utilized for cell growth recovery. Here, we systematically disrupted the biosynthesis of GL, PHB and/or H-2 and examined changes on amount of the remaining bioproducts. Disruption of PHB synthesis increased H-2 evolution rate up to 1.7-fold under -N. Disruption of GL synthesis increased PHB level up to 1.4-fold, but did not affect H-2 production under -N. Cellular NAD(P)H was elevated 1.6-fold after the disruption of GL synthesis, and by 3.6-fold after the disruption of both GL and PHB synthesis under -N. The double disruption of GL and PHB, GL and H-2, or PHB and H-2, significantly affected the initial (day 0-4) growth rate upon switching from -N to nitrogen repletion (+N). Under -N to +N condition at day 0-4, the disrupted synthesis of both GL and PHB significantly decreased the levels of total proteins, phycobilins, carotenoids, and chlorophyll a by 32%, 44%, 47%, and 59%, respectively. Thus, both PHB and GL storage are likely required for normal growth, as well as for the maximal production of proteins and photosynthetic pigments upon growth recovery under nitrogen repletion. The results demonstrated that the cyanobacterial production of GL, PHB, H-2, NAD(P)H, and proteins can be affected by the disruption of metabolically connected biosynthetic pathway(s).

Automated summary

This study found that under nitrogen deprivation, the growth and protein synthesis of Synechocystis sp. PCC 6803 were inhibited while the production of glycogen and poly-3-hydroxybutyrate was enhanced. Disruption of glycogen and poly-3-hydroxybutyrate synthesis affected the production of hydrogen and cellular NAD(P)H differently. Glycogen and poly-3-hydroxybutyrate storage are important for normal growth and maximal production of proteins and photosynthetic pigments.