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Acetate Metabolism in the Purple Non-sulfur Bacterium Rhodobacter capsulatus

E. P. Petushkova and A. A. Tsygankov*

Institute of Basic Biological Problems, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia; E-mail: ttt-00@mail.ru

* To whom correspondence should be addressed.

Received July 14, 2016; Revision received December 30, 2016
The purple non-sulfur bacterium Rhodobacter capsulatus B10 can grow on acetate as the sole carbon source under photoheterotrophic conditions. It is known that the bacterium can use the glyoxylate cycle and, in addition to it, or alternatively to it, an unknown pathway for acetate assimilation. We analyzed the genetic potential for functioning of additional metabolic pathways of oxaloacetic acid (OAA) pool replenishment in R. capsulatus. Using published microarray data of more than 4000 transcripts of genes for R. capsulatus, the genes necessary for acetate assimilation were analyzed. The results of the analysis showed the presence of all genes necessary for functioning of the ethylmalonyl-CoA pathway, and also a combination of pathways of formation of pyruvic acid/phosphoenol pyruvate (PA/PEP) (from acetyl-CoA and formate, from acetyl-CoA and CO2, as well as from 3-phosphoglyceric acid formed in the Calvin–Benson cycle) with their subsequent carboxylation. Using expression analysis, we showed that OAA pool replenishment on acetate medium could be achieved via a combination of PA/PEP synthesis from Calvin–Benson cycle intermediates and their carboxylation (with participation of pyruvate carboxylase, two reversible malate dehydrogenases (decarboxylating) and PEP-carboxykinase) to tricarboxylic acid cycle intermediates, the glyoxylate cycle, and a modified ethylmalonyl-CoA pathway in R. capsulatus under these experimental conditions. It was found that analogs of ethylmalonyl-CoA pathway enzymes exist. These enzymes differ in their specificity for S-enantiomers.
KEY WORDS: Rhodobacter capsulatus, acetate assimilation, glyoxylate cycle, Calvin–Benson cycle, pyruvate oxidoreductase, ethylmalonyl-CoA pathway, methylcitrate cycle

DOI: 10.1134/S0006297917050078