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Synthetic Chloroplasts
Shannon Duffy
Origin of the Chloroplast
• The chloroplast was originally a photosynthetic
prokaryote
• A eukaryotic cell containing a mitochondria engulfed the
prokaryote, and an endosymbiotic relationship was
formed
• The prokaryote evolved to become the chloroplast
organelle
Palma A. Silver
• Leader of the team researching an endosymbiosis
between Synechococcus elongatus and zebrafish embryos
• Also experimented on the possibility of endosymbiosis
with E. coli
• Endosymbiosis:
o Symbiosis where one organism lives within the other
Synechococcus elongatus and
Zebrafish
• Synechococcus elongatus pcc 7942:
o Cyanobacteria that produces energy through photosynthesis and
naturally fluorescent
• Zebrafish embryos:
o Eukaryotes in the earliest stage of development
o Produce no pigment, allowing light to pass through
o Easy to microinject and well studied
Insertion into Zebrafish Embryos
• Three ways to insert the bacteria into an animal cell in a
lab
o Inject live into the animal cell
o Engineer the bacteria to be able to invade the animal cell
o Engineer the bacteria to be digested by the cell
Injection
• While the zebrafish were in the one-cell stage, they were
microinjected with live S. elongatus or E. coli
• The development of the embryos could be monitored with
a fluorescence dissecting microscope
Results
• Red fluorescent bacteria were found in cell throughout
the development with no appearance of affecting the
growth
• The S. elongatus survived for twelve days until the
experiment was terminated
• However, the E. coli killed the zebrafish within two hours
even when the E coli were killed prior to the experiment
with UV rays
Results
Invasion
• The Synechococcus elongatus were engineered with
invasin from Yersinia pestis, and Listeriolysin O from
Listeria monocytogenes
• Invasin: a protein that causes an uptake in bacterial cells
• Listeriolysin O: hemolysin that allows bacteria to enter
the cytoplasm after the uptake
Results
• 4.8% of the mammalian cells were positive for red
autofluorescence
• The cells were sorted based on their fluorescence, and it
was determined that there was approximately one bacteria
per cell
Phagocytosis
• Bacteria can also enter cells through phagocytosis, but for
symbiotic growth, the bacteria also needs to escape
digestion by the lysosome
• Plates were incubated with macrophages and either E.
coli or S. elongatus
Results
• Similar to the zebrafish embryos, the E. coli that were
engulfed quickly killed the macrophage, and those
expressing listeriolysin could kill the macrophage even
faster
• But, the S. elongatus could remain inside the macrophage
for up to two days with little effect
• After two days the macrophage died containing both
Synechococcus with an empty vector and those
expressing invasin and listeriolysin
Results
Additional Research
• Kwang W. Jeon researched creating an endosymbiotic
relationship between an amoeba and its infectant, a
naturally occurring parasitic bacteria
• Over time, some of the surviving amoebae became
dependent on the bacteria within their cells
• This is because the amoebae no longer produced a protein
that was required for survival, because the bacteria were
providing that protein
• So if the bacteria were removed, the amoebae’s nucleoli
were damaged, because the amoebae could no longer
produce the protein
Conclusion
• It was established by Jeon that an endosymbiotic
relationship can be created in a lab in only a few years
• Through her experiments, Silver took the first step in
making an endosymbiotic relationship, and with more
time, the zebrafish could become reliant on the
photosynthetic bacteria
• If the endosymbiotic theory is correct, then after the
zebrafish becomes dependent on the Synechococcus
elongatus, the bacteria could evolve into an organelle
with a similar function to chloroplast, and therefor a
synthetic chloroplast