Blinking Bacteria As Biological Sensors

You’re probably aware that making lab organisms – or at least parts of them – glow a certain colour is relatively commonplace. Biologists frequently attach the gene for green fluorescent protein (GFP) or its differently coloured family members to a gene that they’re interested in, so whenever the gene of interest is activated GFP is produced and the relevant target fluoresces, a nice visible marker. 

In the last few years a group of researchers found a way of tying fluorescence to the cycle of bacteria’s biological clocks, producing rhythmic blinking. Last year they managed to coordinate this blinking in large groups of bacteria, which they compare to living neon signs. Now, they’ve shown that this system can be used as a living sensor for environmental pollutants.

From ScienceDaily:

Using the same method to create the flashing signs, the researchers engineered a simple bacterial sensor capable of detecting low levels of arsenic. In this biological sensor, decreases in the frequency of the oscillations of the cells’ blinking pattern indicate the presence and amount of the arsenic poison.

Because bacteria are sensitive to many kinds of environmental pollutants and organisms, the scientists believe this approach could also be used to design low cost bacterial biosensors capable of detecting an array of heavy metal pollutants and disease-causing organisms. And because the sensor is composed of living organisms, it can respond to changes in the presence or amount of the toxins over time unlike many chemical sensors.

“These kinds of living sensors are intriguing as they can serve to continuously monitor a given sample over long periods of time, whereas most detection kits are used for a one-time measurement,” said Jeff Hasty, a professor of biology and bioengineering at UC San Diego who headed the research team in the university’s Division of Biological Sciences and BioCircuits Institute. “Because the bacteria respond in different ways to different concentrations by varying the frequency of their blinking pattern, they can provide a continual update on how dangerous a toxin or pathogen is at any one time.”

They go on to explain that there are too many bacteria on their “microfluidic chips” (up to 60 million cells) for the bacteria to all coordinate in their usual way, which is called quorum sensing (roughly, relaying signaling molecules between them). They found, though, that colonies released gases that could be used to coordinate between them, while cells within colonies still coordinated by quorum sensing.

This is a pretty interesting idea. I trust biologists to be able to make bacteria sensitive to various molecules and react in various ways; I see no reason why bacteria wouldn’t be able to glow different colours based on the environment, for example. There may be more possibilities with living versus non-living sensors simply because of the incredible complexity of living things, which we can take advantage of without reconstructing from the ground up.


Life in the Mariana Trench

The Mariana Trench is the deepest part of the of the world’s oceans, at a maximum known depth of 10.9 kilometres. From Wikipedia: “If Mount Everest, the highest mountain on Earth at 8,850 metres (29,040 ft), was set in the deepest part of the Mariana Trench, there would be 2,060 metres (6,760 ft) of water left above it.” 

Most importantly, “At the bottom of the trench, where the plates meet, the water column above exerts a pressure of 1,086 bars (15,750 psi), over one thousand times the standard atmospheric pressure at sea level.” That, and the fact that light won’t reach that depth, means that life in the Trench (we’re buddies, I can call it “the Trench”) is very different from life as we know it near sea level, as well as difficult to observe. Yet observe it we have.

From LiveScience:

Gigantic amoebas have been found in the Mariana Trench, the deepest region on Earth.

During a July 2011 voyage to the Pacific Ocean chasm, researchers with Scripps Institution of Oceanography at UC San Diego and National Geographic engineers deployed untethered landers, called dropcams, equipped with digital video and lights to explore the largely mysterious region of the deep sea.

The team documented the deepest known existence of xenophyophores, single-celled animals exclusively found in deep-sea environments. Xenophyophores are noteworthy for their size, with individual cells often exceeding 4 inches (10 centimeters), their extreme abundance on the seafloor and their role as hosts for a variety of organisms.

For reference, the average human cell is about ~10 µm in diameter; that means these amoeba’s cells are 10,000 times the size of ours. That’s a big cell.

The researchers spotted the life forms at depths up to 6.6 miles (10,641 meters) within the Sirena Deep of the Mariana Trench…

Scientists say xenophyophores are the largest individual cells in existence. Recent studies indicate that by trapping particles from the water, xenophyophores can concentrate high levels of lead, uranium and mercury and are thus likely resistant to large doses of heavy metals. They also are well suited to a life of darkness, low temperature and high pressure in the deep sea…

The xenophyophores are just the tip of the deep-sea ecosystem iceberg. The expedition also found the deepest jellyfish observed to date, as well as other mysterious animals.

As I’ve said before, finding new species in novel environments like this is important – discoveries could have all kinds of applications. So little of the ocean has been explored that I’m sure there will be many, many discoveries to make in the future.

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