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Partying bacterial biofilms throw out streamers

By Tushna Commissariat at the APS March Meeting in Denver

The word “streamers” doesn’t normally bring bacteria to mind, but it’s all the rage with biophysicists studying the mechanics of bacterial biofilms that grow where there is fluid flowing. A biofilm is any group of microorganisms where cells stick to each other on a surface – either a living or non-living surface will do. A rather simple example of this is the slimy film that develops over our teeth each night.

Biophysicist Knut Drescher from Princeton University gave a fascinating talk at the APS March Meeting on Monday about his research into why biofilms that grow specifically in the presence of a flowing fluid – such as in channels in soil, filtration systems, as well as medical devices such as stents or urinary catheters – are rapidly clogged, causing a variety of problems and infections. Biofilms in such a case form 3D thread-like “streamers” that are responsible for the rapid clogging. It was initially thought that these streamers formed along the walls of the original film and then expanded inwards, but Drescher and colleagues found that it was actually the other way around – the fishing-line-like streamers grew from the middle and rapidly extended outwards, clogging a channel within minutes.

In fact, Dresher explained that the expansion is exponentially fast, meaning that the channel size does not really matter – once the streamer throws out its web, the clogging expansion is very quick. It might take the biofilm much longer to grow, but the streamers themselves are very quick to expand, catching up not only other bacterial cells in the vicinity, but also any other “sticky” cells – in a stent this could mean particles of cholesterol. You can see this in the time-lapse video above of such a biofilm (green) and its streamer (red) forming over a period of 56 hours.

Also a part of the same talk on bacterial physics was Ken Dill from Stony Brook University in New York. He is exploring the effects of physical properties – such as temperature, salt dependency and packing density – on bacterial evolution, rather than traits linked to individual genes. Dill’s work showed that temperature and osmotic pressure exerted on the cell – both things that could cause proteins in the cell to denature, destroying them – play a seemingly key role. In fact, he went one to give an example that seems truly amazing – a random mix of alligator eggs incubated at below 30° would yield 99% female births, while a similar sample incubated above 34° yields 99% males!

Another point that Dill made was regarding the food available to a cell versus its growth rate – the “growth law”. If the cell is provided with an unlimited food supply, it rapidly duplicates – but only up to a point. At that upper limit, the cell can’t efficiently consume the energy while still increasing its duplication rate, suggesting that it learns to optimize its processes.

Also speaking at the talk was Pankaj Mehta from the Boston University Center of Synthetic Biology. Mehta and colleagues look at how sophisticated biological circuits that naturally perform complex bio-computations could be adapted to designing circuits. The main area of the researchers’ work is to understand how cells seemingly learn about their environment and carry out computations. They also study the physical limitations of the thermodynamics of gene circuits – something that is once more determined by an exchange of information with the environment.

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