[en] Background
Purple non-sulfur bacteria display a great metabolic versatility and are able to assimilate volatile fatty acids (VFAs) through photoheterotrophic metabolism. One of these bacteria, Rhodospirillum rubrum S1H, was subsequently selected by the European Space Agency for its ability to metabolize VFAs and to remove them in its bioregenerative life support system.
Objectives
Here we aim to offer a better view of the still misunderstood photoheterotrophic metabolism of butyrate.
Methods
A global understanding of butyrate photoassimilation in purple non-sulfur bacteria was obtained through a multidisciplinary approache including quantitative SWATH-MS proteomic analysis, activity assays, bacterial growth analysis and VFAs consumption monitoring.
Conclusions
Butyrate is partially converted into acetyl-coA. Because R. rubrum is an isocitrate lyase lacking organism, an alternative anaplerotic pathway to glyoxylate cycle should be used to replenish the TCA cycle with intermediates for biosynthesis. We suggest here that butyrate could be converted into propionyl-CoA and succinate through ethylmalonyl-CoA pathway and valine degradation pathway.
We also observed that butyrate assimilation occurs only if carbonate is supplied. In accordance with the observed upregulation of RuBisCO, CO2 fixation is most probably used as redox balancing reaction necessary to sustain butyrate assimilation.
Finally, we showed an inhibition of the butyrate assimilation by acetate when they are provided together at an equivalent net carbon concentration. This effect could be due to the observed downregulation of key enzymes of the butyrate assimilation pathway when acetate is used as carbon source.
Altogether our data allows better understanding of metabolic pathway involved in butyrate photoassimilation in R. rubrum.
