Astrosquid!

By Siouxsie Wiles 27/03/2013 4


What is the value of blue-skies research?

This is a question often asked by politicians and the public. Why should public money be spent funding science that seems to have no obvious benefit beyond generating scientific knowledge? The simple answer is that it can be almost impossible to predict what new avenues that scientific knowledge will open up. Take the Hawaiian bobtail squid, for example. What could studying this little nocturnal hunter possibly lead to? Take a guess. No ideas? Let me help you out.

It lead to the discovery that bacteria are able to communicate with each other, including how they sense when the time is right to turn on genes needed to cause disease. I’m not sure anyone could have seen that coming! Importantly, this research has provided scientists with another potential weapon with which to fight antibiotic resistant superbugs. In a world rapidly running out of antibiotics, we need all the weapons we can get.

This animation was produced with the support of a public engagement grant from the UK Society for Applied Microbiology, to engage the services of graphic artist Luke Harris and his team. Dr Siouxsie Wiles (@SiouxsieW) is a microbiologist and bioluminescence enthusiast who heads up the Bioluminescent Superbugs Group at the University of Auckland in New Zealand. She and her team make nasty bacteria glow in the dark to help understand and combat infectious diseases.

What we couldn’t fit into 3 minutes…

The Hawaiian bobtail squid, Euprymna scolopes, is just 3 cm in length and lives in the shallow moonlit waters off Hawaii. It spends its days sleeping buried in the sand, emerging at night in search of food. It has a very cunning trick to hide its shadow from fish looking for a meal, or from creatures like shrimp that it feeds on. It houses a colony of glowing bacteria (Vibrio fischeri) in a special organ on its underside. These bioluminescent bacteria shine their light down so that to any creatures looking up, the squid just looks like the moon. What is even more clever is that the squid uses its ink sac to match the intensity of moonlight hitting its back, dimming the light from the glowing bacteria as needed. This is important not just for cloudy nights but as the squid moves through different depths of water.

Baby squid are born without V. fischeri or a light organ. Instead they just have a small opening in their mantle (the bulbous bit of their body) that is bathed by sea water. What is incredible is that only V. fischeri can colonise this opening – once they do, the squid cells start to change and the light organ forms. The ability to glow is crucial though – scientists have made versions of V. fischeri which can’t glow and they aren’t able to colonise either.

Adult squid have an ingenious way of ensuring that there is plenty of V. fischeri floating around in the water to colonise baby squid. Each morning, before they settle down in the sand to sleep for the day, they expel 99.9% of the bacteria from their light organ into the sea. This serves another purpose too, ensuring the bacteria left behind in their light organ are constantly growing and have plenty of nutrients. Bacteria that run out of nutrients start to shut down to save energy. Producing light takes quite a bit of energy and the last thing the squid wants is a mantle full of lazy dim bacteria!

When scientists first identified V. fischeri and grew it in the lab they noticed something quite interesting. The bacteria only switch on their light when they have reached a critical population size. This makes perfect sense. There is no point going to all the trouble of making light if it isn’t bright enough to be seen. Each bacterium produces a chemical, called the autoinducer, that diffuses out of the bacterial cell. The more bacteria there are, the more autoinducer is produced. If those bacteria are growing in a confined space like a flask, or the light organ of the squid, the autoinducer will accumulate. Once it reaches a critical concentration, the autoinducer triggers the bacteria to switch on the genes for producing light*. This phenomenon is called quorum sensing.

Scientists then used the bioluminescence reaction to see if other species of bacteria produce autoinducers. Surprise, surprise, it turns out that lots of different bacteria use quorum sensing to signal to each other that they are in the right numbers or environment to do something, which is not worth doing otherwise. From the bacterial form of sex, to swimming, to switching on the genes needed to cause disease in plants, animals and humans. Now we just have to find a way of exploiting this to our advantage!

You can hear me chatting about the squid and quorum sensing on Radio New Zealand’s Nine to Noon programme with Kathryn Ryan here (13’12”):

*For those who really want to know, the autoinducer is the product of the luxI gene. When it reaches a critical concentration, it interacts with the product of the luxR gene, and together this complex binds to a region of DNA upstream of the genes under their control called the lux box which then triggers their transcription.


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