Metabolic Flux Analysis of the Synechocystis sp PCC 6803 Delta nrtABCD Mutant Reveals a Mechanism for Metabolic Adaptation to Nitrogen-Limited Conditions

作者：Nakajima Tsubasa; Yoshikawa Katsunori; Toya Yoshihiro; Matsuda Fumio; Shimizu Hiroshi

来源：Plant and Cell Physiology, 2017, 58(3): 537-545.

DOI：10.1093/pcp/pcw233

• ATP/NADPH ratio
• Isotopically non-stationary metabolic flux analysis
• Metabolic adaptation
• Nitrogen starvation
• Synechocystis sp PCC 6803

Metabolic flux redirection during nitrogen-limited growth was investigated in the Synechocystis sp. PCC 6803 glucosetolerant (GT) strain under photoautotrophic conditions by isotopically non-stationary metabolic flux analysis (INST-MFA). A Delta nrtABCD mutant of Synechocystis sp. PCC 6803 was constructed to reproduce phenotypes arising during nitrogen starvation. The Delta nrtABCD mutant and the wild- type GT strain were cultured under photoautotrophic conditions by a photobioreactor. Intracellular metabolites were labeled over a time course using NaH13CO3 as a carbon source. Based on these data, the metabolic flux distributions in the wild-type and Delta nrtABCD cells were estimated by INST-MFA. The wild-type GT and Delta nrtABCD strains displayed similar distribution patterns, although the absolute levels of metabolic flux were lower in Delta nrtABCD. Furthermore, the relative flux levels for glycogen metabolism, anaplerotic reactions and the oxidative pentose phosphate pathway were increased in Delta nrtABCD. This was probably due to the increased expression of enzyme genes that respond to nitrogen depletion. Additionally, we found that the ratio of ATP/NADPH demand increased slightly in the Delta nrtABCD mutant. These results indicated that futile ATP consumption increases under nitrogen-limited conditions because the Calvin-Benson cycle and the oxidative pentose phosphate pathway form a metabolic futile cycle that consumes ATP without CO2 fixation and NADPH regeneration.

• 出版日期2017-3