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No matter how many times it is demonstrated, it’s still difficult to envision bacteria as social creatures with the ability to communicate. These simple, tiny, single-celled prokaryotes use a signaling system called ‘quorum sensing” to alter their behavior to suit the size of their population. What this means is that the bacteria actually ‘know” how many of them are present at that particular time. This “knowledge” is carried in small molecules that the lead bacteria release and the other bacteria then pick up by diffusion through their cell membrane. Previous research has shown that bacteria use quorum sensing in a number of different ways. Some bacteria use it to monitor population size in a host organism. Once they get to a certain number, they release disease-causing chemicals and overwhelm their hosts’ immune system.

The latest study involves using chemicals that mimic quorum sensing in order to control the growth of pathogenic bacteria such as salmonella or shingella. Many of these strains are resistant to most antibiotics, but when given the quorum sensing chemical mimics the bacteria stay “tame” and do not give off their pathogenic chemicals, thus allowing the body’s own immune system to wipe out the bacteria.

Use the results of the controlled experiment below, which shows the growth of shingella bacteria on agar plates with the growth of shingella bacteria on agar plates with various additives to the media (all plates have different components), as well as the information in the initial passage to answer questions 4-6 below.

Each plate is initially swabbed with 1000 colonies of shingella bacteria. All plates are incubated at 37 degrees Celsius.

Key to Data Table:

NA=Normal Agar

S=Shingella Antibiotic added to medium

Q=Quorum sensing mimic chemical added to medium

H=Human anti-shingella antibodies added to medium

$$ \text{Number of Colonies (in thousands)} $$

     Media Plate         0 Hours 6 Hours 12 Hours 18 Hours 24 Hours 48 Hours
1) $NA$ 1 5 25 75 100 350
2) $NA + S$ 1 2 7 15 35 100
3) $NA + Q$ 1 1.5 1.5 1.75 2 2
4) $NA + H$ 1 1.5 2.5 10 25 75
5) $NA + S + H$ 1 1 1.8 2.6 2.8 3.3
6) $NA + Q + H $ 1 1 1.5 .75 .01 .005

After the research is published, another scientist releases this statement:

“Quorum sensing chemicals have been discovered that direct soil bacteria that infect soybean roots to harvest more nitrogen from the atmosphere and improve crop yields.”

Based on this information, a possible new line of research that could be followed would be


the use of Shingella bacteria to increase nitrogen production in various plants.


design a controlled experiment that tests the new chemical’s effectiveness against pathogenic bacteria.


design a controlled experiment to test the possibility that quorum chemicals may be beneficial to the environment.


combine the new chemicals with human antibodies to derive a vaccine against Shingella bacteria

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