Abstract: “Plants and algae conduct photosynthesis through chloroplasts, organelles descended from ancient endosymbiotic cyanobacteria. Despite the fundamental importance of endosymbiosis to the evolution of the eukaryotic cell, we have little practical understanding of how a bacterium was converted into an organelle. I am investigating the early stages of this endosymbiotic event in a laboratory setting by engineering eukaryote/prokaryote chimeras. This can be done by fusing a genetically tractable cyanobacterium with a model yeast cell to generate an endosymbiotic cyanobacterium which can survive and divide within the yeast cytosol. In this system, an auxotrophic cyanobacterium is inserted into a respiration-deficient yeast cell where it provides ATP and/or assimilated carbon (e.g. glucose) generated by photosynthesis. In return, the yeast cytosol provides an essential metabolite to the cyanobacterium. We have observed that mutant cyanobacteria can survive within yeast for multiple generations and can be engineered to enhance growth and longevity of the chimeras. I envision that the existing model may be further optimized to perform many downstream functions, including i) secretion of photosynthetic end-products, ii) host/symbiont protein exchange and iii) genome minimization and evolutionary studies.”
Engineering a photosynthetic yeast through endosymbiosis – transcript
Nice talk! The model you are studying seems robust. Your future work proposed is to study endosymbiosis with gram positive bacteria- do you envision any problems due to the thick layer of peptidoglycans on their cell wall? If so, please explain.
Nice talk! How generalizable do you think this approach of replicating endosymbiosis is?
The project of endosymbiosis has been done before, with one case between E. Coli and yeast cells (citation 2 in presentation) and another case with S. elongatus and zebrafish mammalian cells (citation 3 in presentation). When it comes to general choices of eukaryotes and prokaryotes, size is definitely one of the deciding factor for viability. The prokaryote should not take up too much space surviving inside the eukaryote.
As I mentioned during the presentation, observing a true endosymbiotic relationship requires deleting key biosynthetic genes from both the host and the endosymbionts. Methods of gene targeting can vastly vary between different cells. When it comes to working with other possible cell candidates, we need to first learn how to modify its genomic DNA.
We chose yeast cell as our eukaryote for this project because we know a consistent way to remove its cell wall in order for S. elongatus to enter it. If any other eukaryotes are capable of surviving with its cell wall removed temporarily, that can potentially be viable as well.
Given what we have studied about S. elongatus and zebrafish mammalian cells from the article, it seems that S. elongatus is very well tolerated under endosymbiotic relationship, as it can propagate robustly.
So far there are works of E. Coli, a gram-negative bacteria, in endosymbiotic studies. In the future of this project, we would like to work with gram-positive bacteria and test its viability.
Notes:
Citation 2 in text:
Mehta, A. P.; Supekova, L.; Chen, J.-H.; Pestonjamasp, K.; Webster, P.; Ko, Y.; Henderson, S. C.; McDermott, G.; Supek, F.; Schultz, P. G. Engineering Yeast Endosymbionts as a Step toward the Evolution of Mitochondria.)
Citation 3 in text:
Agapakis, C. M.; Niederholtmeyer, H.; Noche, R. R.; Lieberman, T. D.; Megason, S. G.; Way, J. C.; Silver, P. A. Towards a Synthetic Chloroplast