Flexibility in Anaerobic Metabolism as Revealed in a Mutant of Chlamydomonas reinhardtii Lacking Hydrogenase Activity

被引:75
作者
Dubini, Alexandra [1 ,2 ]
Mus, Florence [4 ]
Seibert, Michael [1 ]
Grossman, Arthur R. [4 ]
Posewitz, Matthew C. [1 ,3 ]
机构
[1] Natl Renewable Energy Lab, Golden, CO 80401 USA
[2] Colorado Sch Mines, Environm Sci & Engn Div, Golden, CO 80401 USA
[3] Colorado Sch Mines, Dept Chem & Geochem, Golden, CO 80401 USA
[4] Carnegie Inst Sci, Dept Plant Biol, Stanford, CA 94305 USA
基金
美国国家科学基金会; 美国能源部;
关键词
PYRUVATE FORMATE-LYASE; GENE-EXPRESSION; SUCCINIC ACID; SULFATE RESPIRATION; H-2; PRODUCTION; ATP SYNTHESIS; GREEN-ALGAE; EVOLUTION; PATHWAYS; INSIGHTS;
D O I
10.1074/jbc.M803917200
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
The green alga Chlamydomonas reinhardtii has a network of fermentation pathways that become active when cells acclimate to anoxia. Hydrogenase activity is an important component of this metabolism, and we have compared metabolic and regulatory responses that accompany anaerobiosis in wild-type C. reinhardtii cells and a null mutant strain for the HYDEF gene (hydEF-1 mutant), which encodes an [FeFe] hydrogenase maturation protein. This mutant has no hydrogenase activity and exhibits elevated accumulation of succinate and diminished production of CO2 relative to the parental strain during dark, anaerobic metabolism. In the absence of hydrogenase activity, increased succinate accumulation suggests that the cells activate alternative pathways for pyruvate metabolism, which contribute to NAD(P)H reoxidation, and continued glycolysis and fermentation in the absence of O-2. Fermentative succinate production potentially proceeds via the formation of malate, and increases in the abundance of mRNAs encoding two malate-forming enzymes, pyruvate carboxylase and malic enzyme, are observed in the mutant relative to the parental strain following transfer of cells from oxic to anoxic conditions. Although C. reinhardtii has a single gene encoding pyruvate carboxylase, it has six genes encoding putative malic enzymes. Only one of the malic enzyme genes, MME4, shows a dramatic increase in expression (mRNA abundance) in the hydEF-1 mutant during anaerobiosis. Furthermore, there are marked increases in transcripts encoding fumarase and fumarate reductase, enzymes putatively required to convert malate to succinate. These results illustrate the marked metabolic flexibility of C. reinhardtii and contribute to the development of an informed model of anaerobic metabolism in this and potentially other algae.
引用
收藏
页码:7201 / 7213
页数:13
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