Abstract
BackgroundThe evolution of eukaryotic cells is widely agreed to have proceeded through a series of endosymbiotic events between larger cells and proteobacteria or cyanobacteria, leading to the formation of mitochondria or chloroplasts, respectively. Engineered endosymbiotic relationships between different species of cells are a valuable tool for synthetic biology, where engineered pathways based on two species could take advantage of the unique abilities of each mutualistic partner.ResultsWe explored the possibility of using the photosynthetic bacterium Synechococcus elongatus PCC 7942 as a platform for studying evolutionary dynamics and for designing two-species synthetic biological systems. We observed that the cyanobacteria were relatively harmless to eukaryotic host cells compared to Escherichia coli when injected into the embryos of zebrafish, Danio rerio, or taken up by mammalian macrophages. In addition, when engineered with invasin from Yersinia pestis and listeriolysin O from Listeria monocytogenes, S. elongatus was able to invade cultured mammalian cells and divide inside macrophages.ConclusionOur results show that it is possible to engineer photosynthetic bacteria to invade the cytoplasm of mammalian cells for further engineering and applications in synthetic biology. Engineered invasive but non-pathogenic or immunogenic photosynthetic bacteria have great potential as synthetic biological devices.
Highlights
While the evolution of cooperation and altruism are often seen as paradoxical events in the course of natural selection, endosymbiosis has been recognized as a driver of evolutionary change
Symbiosis is generally thought to refer to a mutualistic relationship where both partners benefit, but the term can be construed rather broadly; Lynn Margulis paraphrases de Bary’s 1879 definition of symbiosis as the ‘‘protracted physical associations among organisms of different species, without respect to outcome.’’ [18] We explored three paths for entry of photosynthetic bacteria into animal cells that would satisfy this broad definition of symbiosis—direct microinjection into zebrafish embryos to explore the in vivo dynamics in a whole animal model, engineering with invasin from Y. pestis and listeriolysin O from L. monocytogenes to allow invasion of mammalian endothelial cells, and endocytosis of inv and llo engineered strains by macrophages
Plasmids and DNA construction The invasin gene from Yersinia pestis was subcloned from the pAC-TetInv plasmid [16] provided by Chris Voigt (University of California, San Franscisco) and listeriolysin O was amplified from Listeria monocytogenes genomic DNA provided by Heather Kamp (Harvard Medical School, Boston MA)
Summary
While the evolution of cooperation and altruism are often seen as paradoxical events in the course of natural selection, endosymbiosis has been recognized as a driver of evolutionary change. Multicomponent synthetic-ecological systems have been developed for hydrogen production through metabolic engineering [9] and for the production of other useful metabolites [10]. Engineered communities have been useful as a generalized model of cooperation and competition in microbial populations [13,14] and two-species metabolic modeling has been used in the identification of cooperating variants of E. coli [15]. The evolution of eukaryotic cells is widely agreed to have proceeded through a series of endosymbiotic events between larger cells and proteobacteria or cyanobacteria, leading to the formation of mitochondria or chloroplasts, respectively. Engineered endosymbiotic relationships between different species of cells are a valuable tool for synthetic biology, where engineered pathways based on two species could take advantage of the unique abilities of each mutualistic partner
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