A proposed citramalate cycle for acetate assimilation in the purple non-sulfur bacterium Rhodospirillum rubrum

Abstract During phototrophic growth on acetate and CO2Rhodospirillum rubrum 2R contained malate synthase but lacked isocitrate lyase. Acetate assimilation by R. rubrum cells was stimulated by pyruvate, propionate glyoxylate, CO2 and H2. Acetate photoassimilation by R. rubrum cells in the presence of...

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Bibliographic Details
Published in:FEMS microbiology letters 1997-08, Vol.153 (2), p.399-404
Main Authors: Ivanovsky, Ruslan N, Krasilnikova, Elena N, Berg, Ivan A
Format: Article
Language:English
Subjects:
Acetate
Acetic acid
Assimilation
Bicarbonates
Carbon dioxide
Citramalate
Glyoxylate
Isocitrate lyase
Malate synthase
Microbiology
Oxidation
Propionic acid
Pyruvate synthase
Pyruvic acid
Rhodospirillum rubrum
Sulfur
Tricarboxylic acid cycle
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Summary:Abstract During phototrophic growth on acetate and CO2Rhodospirillum rubrum 2R contained malate synthase but lacked isocitrate lyase. Acetate assimilation by R. rubrum cells was stimulated by pyruvate, propionate glyoxylate, CO2 and H2. Acetate photoassimilation by R. rubrum cells in the presence of bicarbonate was accompanied by glyoxylate secretion, which increased after addition of fluoroacetate and decreased after addition of malonate. When acetyl-CoA was incubated with pyruvate in cell-free extracts, citramalate was formed. Citramalate was also formed from propionyl-CoA and glyoxylate. The existence in R. rubrum of a CO2-dependent cyclic pathway of acetate oxidation to glyoxylate with citramalate as an intermediate is proposed. Inhibitor analysis of acetate and bicarbonate assimilation indicated that pyruvate synthase is not involved in acetate assimilation in R. rubrum. The possible anaplerotic sequences employed by R. rubrum during phototrophic growth on acetate are discussed.
ISSN:0378-1097
1574-6968
DOI:10.1111/j.1574-6968.1997.tb12602.x