title: Synthetic photosynthetic consortia define interactions leading to robustness and photoproduction.
abstract: BACKGROUND
  Microbial consortia composed of autotrophic and heterotrophic species abound in nature, yet examples of synthetic communities with mixed metabolism are limited in the laboratory. We previously engineered a model cyanobacterium,Synechococcus elongatusPCC 7942, to secrete the bulk of the carbon it fixes as sucrose, a carbohydrate that can be utilized by many other microbes. Here, we tested the capability of sucrose-secreting cyanobacteria to act as a flexible platform for the construction of synthetic, light-driven consortia by pairing them with three disparate heterotrophs:Bacillus subtilis, Escherichia coli, orSaccharomyces cerevisiae. The comparison of these different co-culture dyads reveals general design principles for the construction of robust autotroph/heterotroph consortia.
  
  
  RESULTS
  We observed heterotrophic growth dependent upon cyanobacterial photosynthate in each co-culture pair. Furthermore, these synthetic consortia could be stabilized over the long-term (weeks to months) and both species could persist when challenged with specific perturbations. Stability and productivity of autotroph/heterotroph co-cultures was dependent on heterotroph sucrose utilization, as well as other species-independent interactions that we observed across all dyads. One destabilizing interaction we observed was that non-sucrose byproducts of oxygenic photosynthesis negatively impacted heterotroph growth. Conversely, inoculation of each heterotrophic species enhanced cyanobacterial growth in comparison to axenic cultures. Finally, these consortia can be flexibly programmed for photoproduction of target compounds and proteins; by changing the heterotroph in co-culture to specialized strains ofB. subtilisorE. coliwe demonstrate production of alpha-amylase and polyhydroxybutyrate,respectively.
  
  
  CONCLUSIONS
  Enabled by the unprecedented flexibility of this consortia design, we uncover species-independent design principles that influence cyanobacteria/heterotroph consortia robustness. The modular nature of these communities and their unusual robustness exhibits promise as a platform for highly-versatile photoproduction strategies that capitalize on multi-species interactions and could be utilized as a tool for the study of nascent symbioses. Further consortia improvements via engineered interventions beyond those we show here (i.e., increased efficiency growing on sucrose) could improve these communities as production platforms.
authors.affiliation: Department of Systems Biology, Harvard Medical School, Boston, MA USA.|Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA USA.
authors.forename: Stephanie G
authors.initials: SG
authors.lastname: Hays
authors.affiliation: MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, MI USA.|Department of Biology, Washington University in St. Louis, St. Louis, MO USA.
authors.forename: Leo L W
authors.initials: LLW
authors.lastname: Yan
authors.affiliation: Department of Systems Biology, Harvard Medical School, Boston, MA USA.|Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA USA.
authors.forename: Pamela A
authors.initials: PA
authors.lastname: Silver
authors.affiliation: MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, MI USA.|Department of Biochemistry & Molecular Biology, Michigan State University, East Lansing, MI USA.
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Ducat
keywords: Microbial communities; Photoproduction; Synthetic biology; Synthetic consortia