Glycine Cleavage Powers Photoheterotrophic Growth of Chloroflexus aurantiacus in the Absence of H 2.

Lian He,Le You,Yinjie J Tang,Yaya Wang,Joseph K.-H Tang,Yadana Khin

doi:10.3389/fmicb.2015.01467

Abstract

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.

Highlights

Chloroflexus aurantiacus is a filamentous anoxygenic phototrophic bacterium isolated from hot springs (Hanada and Pierson, 2006)
Strain J-10-fl supplied with yeast extract reached an OD above 1.0 within 6 days during photoheterotrophic growth
The study indicated that glycine could participate in serine synthesis and contribute approximately half of the C1 units to biomass synthesis

Summary

Introduction

Chloroflexus aurantiacus is a filamentous anoxygenic phototrophic bacterium isolated from hot springs (Hanada and Pierson, 2006). It has specialized light-harvesting antenna machines and performs a cyclic photosynthetic electron transport via a type II reaction center (Tang and Blankenship, 2013). The genome of C. aurantiacus strain J-10-fl has been sequenced to facilitate our understanding of its physiology and cellular metabolism (Tang et al, 2011). C. aurantiacus switches to photoheterotrophic growth when supplied with acetate under anaerobic and light conditions. In the presence of H2/CO2, C. aurantiacus can perform a photoautotrophic growth by fixing CO2 via the 3-hydroxypropionate (3HOP) bi-cycle pathway (Eisenreich et al, 1993; Zarzycki et al, 2009)

Methods

Results

Conclusion