DNA is the programming within a cell.

Cells can be reprogrammed by humans to act as sensors or to complete more complex tasks.

Plasmids are small DNA messages that can be used by bacteria to alter their programming and behavior.

Bacterial biosensors are sensors that use genetically altered bacteria to detect the presence of chemicals.

Sensor

Bacterial Biosensor

Genetic Engineering

Plasmid

Intro to Bacterial Biosensors Virtual Worksheet

Can be done individually or as a jigsaw among a group of 3-4 students

1 hour

An understanding of the basics of cell biology is helpful, particularly the central dogma (DNA –> RNA –> Protein).

• Reinforce DNA as the cell’s program/instructions. Develop student’s understanding that by altering the cell’s genes, the cells gain new functions and behaviors.
• Introduce the concept of a biosensor, a cell that acts as a living sensor.
• Introduce to students the idea that cells can be engineered to solve problems.

Biosensors are living sensors that detect chemicals in the environment. A very simple example of a biosensor is a canary in a coal mine. The canary would die if certain toxic substances were in the air, but at significantly lower concentrations than would be deadly to humans. Many cellular biosensors are similar, used to detect toxic substances at concentrations far lower than humans can detect.  In this lesson, the sensor is made from e. coli bacteria. By altering and implanting plasmid DNA (a small loop of DNA commonly found in bacteria) into the e. coli bacteria, they can be converted into a biosensor that detects some chemical and responds by changing color (by turning on a gene that produce a pigment or a chemical compound that glows, like GFP).

Often the genes that are used to detect chemicals and change the color of the bacteria are genes already found in nature in some other species.  For example, there are bacteria that make their homes in toxic environments (like C. Metallidurans) that already have lead detecting genes.  And there are some organisms that glow (like A. Victoria, a fluorescent jellyfish).  When cellular engineers combine these two genes, they make sure that the glowing gene will only activate after the lead gene has activated (after the cell detects lead in the environment), thus ensuring that the new bacteria will only glow when lead is present. Thus, this biosensor would detect lead and glow as a result.

These bacterial biosensors can be used on their own (i.e. you can grow a bacterial biosensor in a petri dish or test tube, expose it to a water sample, wait, and use your eyes to detect any glow or change in color), but often cellular engineers will go a step beyond and create a device that surrounds the bacteria biosensor to make it easier, safer, and more accurate to use. For example, instead of growing the bacterial biosensor inside a petri dish, engineers have created small pill shaped containers for the biosensors so that they can be swallowed safely by patients, or small devices that attach directly to the water supply to be tested.  In either case, the bacteria are enclosed inside the device, but have access to the environment through a permeable membrane (that allows small chemical compounds through, but prevents the engineered bacteria from escaping the device).

Additionally, to automate the process, engineers might add a camera or other light sensor to automatically detect even small changes in bacteria color.  This camera could be connected to a wireless transmitter to allow collection of data even when the bacterial biosensor device is inaccessible (inside a patient or attached to plumbing).  But it’s important to remember that these technical additions are not the biosensor. The biosensor is the genetically altered bacteria. The container and/or cameras added around the bacterial biosensor just make the biosensor easier to use and read.

Introduction (10 mins):

Let students know that today they will be learning about bacterial biosensors. Ask students what they think a bacterial biosensor might be. Allow them to make predictions, either aloud or written. Likely, at least one student will predict that a bacterial biosensor detects bacteria.  Let them know that a bacterial biosensor is actually a sensor made of a bacteria (This is a common student misconception, and will likely pop up again! Make sure to check in with your students so that this assumption doesn’t confuse them).  Inside a bacterial biosensor, the genes of the bacteria have been altered to detect some “chemical” and respond by doing something.  Ask student for some examples of chemicals (lead, salt (NaCl), iron, water, etc.)

Activity (40 mins):

Let the student know they will be learning about three different bacterial biosensors that detect three different “chemicals”.  They will need to watch the videos and read the articles to find what each bacterial biosensor detects and how each bacterial biosensor responds to let the scientist know the “chemical” was found.  Have students partner with another student to share their answers and discuss what was surprising, or what questions they still have.

Many students get confused about what a bacterial biosensor is.  Because the articles and videos talk about the mechanical devices surrounding the bacteria, students often assume the sensor is the mechanical device around the bacteria and not the bacteria themselves.  Ask students if they know what part of the device is actually detecting the chemical for each example? (answer: the bacteria)  Is the device detecting bacteria (or chemicals made by a bacteria)? (answer: no) Would the devices work to detect the chemical without the bacteria? (answer: no)

The Bioethics (Portobello Colegio and the UCSF Biosensor) is a great extension after students have completed this activity.  While it doesn’t require extensive understanding of the science of a biosensor, student will benefit from having a firm foundational understanding of biosensors before engaging in the ethical case study that is the focus of the Bioethics lesson. 

ETS2 Links Among Engineering, Technology, Science, and Society

HS-LS1-1 From Molecules to Organisms: Structures and Processes

(The plasmid DNA determines the structure of the pigment or fluorescent protein, which allows bacteria to change color or glow.)

HS LS1.A Structure and Function

ETS2.A Interdependence of Science, Engineering, and Technology

(Science and engineering are linked and use similar tools to answer complex questions. In this example, the bacteria functions as a sensor to detect harmful chemicals. Engineers use the knowledge that scientists have generated about bacteria and how the function to create new bacteria that can be used as sensors.)

Practice 4. Analyzing and Interpreting Data

Practice 8. Obtaining, Evaluating, and Communicating Information

Cause and Effect

Structure and Function