RESEARCH HIGHLIGHTS

ENVIRONMENTAL Disentangling syntrophy

Syntrophic interactions, in which direct electron transfer. These models intraspecies transfer rather two or more coop- were combined to provide an inte- than by DIET. Comparative analysis erate metabolically to metabolize grated genomic model of syntrophy, of the different modes of electron compounds that neither partner can introducing a shared metabolite pool transfer identified several factors that metabolize alone, are common in component to allow for the exchange influence which mode of transfer is environmental niches. Zengler and of metabolites both between preferred, including the local avail- colleagues present a ‘multi-omics’, and with the external environment. ability of protons. systems-based workflow to investigate The electron transfer flux constraint Finally, the authors investigated the details of a syntrophic relationship was defined, which enabled DIET the adaptations that occured dur- between two Geobacter species. to be modelled. Physiological and ing syntrophic growth and found Syntrophy that involves interspe- transcriptomic data were also added that adaptation involved genomic cies electron transfer is often found into the mix. and transcriptomic changes in the in methanogenic environments. The results confirmed that DIET dominant partner, G. sulfurreducens, Although this is mostly thought to was the main mode of electron whereas only transcriptomic changes involve interspecies hydrogen transfer, transfer from G. metallireducens to were observed in G. metallireducens. direct interspecies electron transfer G. sulfurreducens, and showed that This led the authors to suggest that, in (DIET) has been observed in some — in addition to oxidation syntrophic associations, the electron- methanogenic syntrophies. One and fumarate reduction — nitrogen accepting partner may undergo meta- such laboratory-evolved association fixation by G. sulfurreducens was also bolic streamlining to favour the most involves Geobacter metallireducens essential. Transcriptomic analysis of two efficient mode of electron transfer. and Geobacter sulfurreducens, mutant strains of G. metallireducens Sheilagh Molloy which can grow syntrophically revealed that optimal electron flux on ethanol and fumarate using via DIET required transfer. ORIGINAL RESEARCH PAPER Nagarajan, H. et al. DIET from G. metallireducens to To gain an insight into the factors Characterization and modelling of interspecies electron transfer mechanisms and microbial G. sulfurreducens. that determine whether interspe- community dynamics of a syntrophic association. The authors updated the genome- cies hydrogen transfer or DIET Nature Commun. http://dx.doi.org/10.1038/ ncomms3809 (2013) scale metabolic reconstructions that is preferred, the authors replaced FURTHER READING Zengler, K. & Palsson, B. O. are available for both partners, to G. metallireducens with Pelobacter A roadmap for the development of community account for the energy carbinolicus, which exchanges systems (CoSy) . Nature Rev. Microbiol. 10, 366–372 (2012) that is involved in extracellular and electrons with G. sulfurreducens by

NATURE REVIEWS | MICROBIOLOGY VOLUME 12 | JANUARY 2014

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