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Title: Assessment of photosynthesis regulation in mixotrophically cultured microalga Chlorella sorokiniana

Mixotrophic growth of microalgae offers great potential as an efficient strategy for biofuel production. In this study, photosynthetic regulation of mixotrophically cultured Chlorella sorokiniana cells was systematically evaluated. Mixotrophic cells in the exponential growth phase showed the highest photosynthetic activity, where maximum photosynthetic O2 evolution was approximately 3- and 4-fold higher than cells in the same phase grown photoautotrophically in 1% CO2 (in air) and air, respectively. Additionally, characteristic chlorophyll fluorescence parameters demonstrated that no limitation in electron transport downstream of PSII was detected in mixotrophic cells. Up-regulation of photosynthetic activity was associated with high total ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylase activity and expression level of phosphoribulokinase (PRK). After 3 days, photosynthetic O2 evolution of mixotrophic cells that went to the stationary phase, was strongly reduced, with reduced photochemical efficiency and reorganization of the PSII complex. Simultaneously, enzymatic activity for Rubisco carboxylase and mRNA levels of Rubisco and PRK diminished. Importantly, there was almost no non-photochemical quenching for mixotrophic cells, whether grown in log or stationary phase. A decline in the quantum efficiency of PSII and an oxidized plastoquinone pool (PQ pool) was observed under N-depleted conditions during mixotrophic growth. Finally, these results demonstrate that photosynthesis is regulated differently inmore » mixotrophically cultured C. sorokiniana cells than in cells grown under photoautotrophic conditions, with a particularly strong impact by nitrogen levels in the cells.« less
 [1] ;  [1] ;  [1] ;  [2] ;  [1] ;  [3] ;  [1] ;  [1]
  1. Washington State Univ., Pullman, WA (United States)
  2. Johns Hopkins Univ., Baltimore, MD (United States)
  3. National Renewable Energy Lab. (NREL), Golden, CO (United States)
Publication Date:
OSTI Identifier:
Report Number(s):
Journal ID: ISSN 2211-9264
Grant/Contract Number:
AC36-08GO28308; EE0003112
Accepted Manuscript
Journal Name:
Algal Research
Additional Journal Information:
Journal Volume: 19; Journal ID: ISSN 2211-9264
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
Country of Publication:
United States
09 BIOMASS FUELS; 59 BASIC BIOLOGICAL SCIENCES; microalgae; Chlorella sorokiniana; mixotrophic; photosynthesis