Altered Fermentative Metabolism in Chlamydomonas reinhardtii Mutants Lacking Pyruvate Formate Lyase and Both Pyruvate Formate Lyase and Alcohol Dehydrogenase
Chlamydomonas reinhardtii, a unicellular green alga, often experiences hypoxic/anoxic soil conditions that activate fermentation metabolism. We isolated three Chlamydomonas mutants disrupted for the pyruvate formate lyase (PFL1) gene; the encoded PFL1 protein catalyzes a major fermentative pathway in wild-type Chlamydomonas cells. When the pfl1 mutants were subjected to dark fermentative conditions, they displayed an increased flux of pyruvate to lactate, elevated pyruvate decarboxylation, ethanol accumulation, diminished pyruvate oxidation by pyruvate ferredoxin oxidoreductase, and lowered H2 production. The pfl1-1 mutant also accumulated high intracellular levels of lactate, succinate, alanine, malate, and fumarate. To further probe the system, we generated a double mutant (pfl1-1 adh1) that is unable to synthesize both formate and ethanol. This strain, like the pfl1 mutants, secreted lactate, but it also exhibited a significant increase in the levels of extracellular glycerol, acetate, and intracellular reduced sugars and a decrease in dark, fermentative H2 production. Whereas wild-type Chlamydomonas fermentation primarily produces formate and ethanol, the double mutant reroutes glycolytic carbon to lactate and glycerol. Although the metabolic adjustments observed in the mutants facilitate NADH reoxidation and sustained glycolysis under dark, anoxic conditions, the observed changes could not have been predicted given our current knowledge of the regulation of fermentation metabolism.
- Research Organization:
- National Renewable Energy Laboratory (NREL), Golden, CO (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23), Genomes to Life Program; National Science Foundation (NSF)
- DOE Contract Number:
- AC36-08GO28308
- OSTI ID:
- 1047348
- Report Number(s):
- NREL/JA-2700-55325
- Journal Information:
- Plant Cell, Journal Name: Plant Cell Journal Issue: 2 Vol. 24
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ALCOHOL DEHYDROGENASE
BUILDUP
CARBON
CHLAMYDOMONAS
DECARBOXYLATION
ETHANOL
FERMENTATION
FERREDOXIN
FORMATES
GLYCEROL
GLYCOLYSIS
LACTATES
LEVELS
LYASES
METABOLISM
MUTANTS
OXIDATION
PRODUCTION
PROTEINS
REGULATIONS
SACCHARIDES
SOILS
anoxic conditions
double mutant
photosynthetic algae