Journal
PLANT CELL
Volume 24, Issue 2, Pages 692-707Publisher
AMER SOC PLANT BIOLOGISTS
DOI: 10.1105/tpc.111.093146
Keywords
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Funding
- Office of Biological and Environmental Research, Genomes to Life Program, Office of Science, U.S. Department of Energy
- National Renewable Energy Laboratory
- National Science Foundation [MCB-0235878]
- U.S. Department of Energy [DE-FG02-07ER64427, DE-AC36-08GO28308]
- Air Force Office of Scientific Research [FA9550-05-1-0365]
- Scuola Superiore Sant'Anna and Regione Toscana Programma Operativo Regionale Obiettivo 2 Fondo Sociale Europeo
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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 H-2 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 H-2 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.
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