Page 18 - Undergraduate Research Opportunities Program Proceedings 2017-18

School of Science
Division of Life Science

In living organisms such as bacteria, plasmids that carry antibiotic resistances can often be a selective advantage to help
these bacteria survive in harsh environments. However, when not necessary to survive, these plasmids simply become a
replicative burden for the bacteria. Through multiple generations, these plasmids are expected to be lost since
descendants without the plasmid will have a slight advantage in terms of economy over ones with the plasmid. This
report seeks to discuss what happens when the motile E.Coli strain AMB1655 is transformed with Chloramphenicol
resistance (with GFP marker) and Kanamycin resistance (with RFP marker), and allowed to grow in LB without any
selection pressure.

Genetic Identification of Negative Regulator of Bone Morphogenetic Protein Signaling Pathway Negative Regulator

Supervisor: CHOW King Lau / LIFS
Student: CHENG Muyang / SSCI Course: UROP1100, Summer

DBL-1/TGF-β is a signaling molecule that is the Caenorhabditis elegans ortholog for mammalian BMP. It is transduced
through the Sma/Mab pathway and regulates the organism’s body size. As the change in body size at different signaling
strength is often insignificant and inconsistent, it is difficult to monitor signal strength merely by the length of the
organism. Through Gibson assembly, a GFP reporter construct is created by inserting the promoter sequence of a known
DBL-1 responsive gene into a plasmid that drives the expression of GFP. The resulting signal can then be easily recorded
and quantified to represent the signal strength of DBL-1.

Implementation of a Genetic Kill Switch to Control Environmental Release of Genetically Modified Organisms
Supervisor: CHOW King Lau / LIFS
Student: CHEUNG Chun Wai / SSCI Course: UROP1100, Summer

Genetically modified organisms (GMOs) have important uses in industries and researches. Modified genes may spread
when GMOs enter the natural environment, and this could lead to detrimental impacts. To solve this problem, scientists
employed different methods to ensure they can only survive in designated conditions and will be automatically killed
outside contained environment. This project intends to implement a genetic kill switch with combined features of two
reported kill switches, “Deadman” and “Passcode”. The circuit preserves much design of ‘Deadman’ and uses the idea of
hybrid transcription factor (TF) in the ‘Passcode’ circuit to alter the survival environmental signal. Organisms with this
switch should only survive under the presence of N-acyl homoserine lactone (AHL), a quorum sensing molecule of
common gram-negative bacteria, instead of anhydrotetracycline (ATc) in the original ‘Deadman’ circuit.

Supervisor: CHOW King Lau / LIFS
Student: LAM Ka Chung / SSCI Course: UROP1100, Summer

Microbial kill switches have been developed by researchers for bacterial containment purposes. The ‘Passcode’ kill
switch published in 2015 controls cell survival by detecting the presence of a combination of environmental inputs,
enabling the generation of many ‘passcodes’. To develop the kill switch into a secure system, we introduced the concept
of permutation into the kill switch to increase the complexity of the input. In one proposed genetic circuit, two inducers
are the inputs to the kill switch. Using inducible transcriptional repression, antitermination, and a toxin/antitoxin system,
the circuit demonstrates how the kill switch allows cell survival only when the two inducers are inputted in a particular
order.

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