Glycine cleavage powers photoheterotrophic growth of Chloroflexus aurantiacus in the absence of H₂

Chloroflexus aurantiacus is an anoxygenic phototrophic bacterium. Its unique CO₂ fixation pathway and primitive light-harvesting antenna complexes have attracted extensive research attentions. In this work, we investigated the photoheterotrophic growth of C. aurantiacus J-10-fl using acetate [at 55°C and without H₂(g)]. The results indicate that glycine can promote anaerobic biomass production in a minimal medium by threefold to fivefold. Via ¹³C-metabolite analysis, we observed that glycine was involved in serine synthesis. Instead of being used as a major carbon source, glycine was degraded to produce C1 units and NAD(P)H. Tracer experiments also suggest that photoheterotrophic cultures growing with a exogenous glycine source exhibited capabilities of assimilating CO₂ via multiple routes (including the 3-hydroxypropionate pathway). Finally, glycylglycine, a commonly used culture buffer, also significantly enhanced photoheterotrophic growth of C. aurantiacus, probably due to its thermal or enzymatic breakdown to glycine.