Lighthouses and signal fires may have been the first social media. Without the ability to share language, a distant light meant "humans here." A new study from the University of California, San Diego, finds that bacteria can also send out a universal sign to attract the attention of their own, and other bacterial species.
Like humans, bacteria are social creatures. While bacteria exist as individuals, some species prefer to live in communities called biofilms, which are like bacterial burgs or cell cities. Biofilms are cellular communities that can grow anywhere they can get a grip, and right now, you have one coating at least some of your teeth.
Biofilms happen when bacteria decide to settle down. But instead of putting down roots, they grab hold with hairlike pili and produce a sticky goo called extracellular matrix. This compound, composed of proteins and sugar, develops structure and connects and nurtures the microbial community.
Biofilms are essentially mats of microbial life that form on living and non-living things. Think of someplace in your house that is slimy—crud in your kitchen sink, slime around the shower, slippery stuff growing in your coffee machine—you get the idea. The next time you slip on a rock trying to cross a stream, think biofilm. Think of the scum on the inside of pipes, on pool equipment, or the outside of boats. The point is, biofilms can be anywhere conducive to bacterial growth.
Now while that may all sound gross, some biofilms are helpful. In addition to being a natural part of a healthy human body and the environment, biofilms currently have practical uses that include sewage treatment, bioremediation that percolates toxins out of contaminated water, and assistance extracting metals like copper during the mining process.
But biofilms also provide a living space for harmful bacteria. Over time, biofilms grow in layers and spread outward. Using chemical signals within the biofilm, bacteria take on different roles to sustain, maintain, and grow their community. When dangerous bacteria congregate in a biofilm inside the human body, or on medical equipment, the consequences can be dire, as these hearty ecosystems can be more difficult to kill than single bacterial communities.
Just as with human societies, biofilms find strength in numbers. By joining together, bacteria boost their chance of survival—oftentimes in hospital settings where they can infect seriously ill patients.
While the number of drug-resistant bacteria continue to increase, antibiotics are generally still effective against acute common infections. When infections become persistent, or chronic, such as those associated with diabetes, cystic fibrosis, or implanted medical devices, biofilms can prove deadly.
According to the Centers for Disease Control and Prevention, healthcare-acquired infections affect one in 25 hospitalized patients in the United States, and are often associated with non-healing infections caused by biofilms.
Just as a human community fights to survive and repel invaders, so do biofilms. Biofilms excrete a surface barrier that resists antibiotics. Because they live in layers, antibiotics have difficulty penetrating the film's layers, so they are effective only on the fast-growing edge. Slower growing and dormant pathogens within the biofilm remain alive to reactivate and regenerate if enough of the microbial community is damaged.
Against this backdrop, researchers from UC San Diego sought to better understand communication within and beyond biofilms. From their earlier work with biofilms, the research team already understood biofilms use chemical signals to resolve internal social conflicts like periodically slowing outer edge growth to ensure interior cells do not starve.
In recent research published in Cell, the team discovered that biofilms composed of Bacillus subtilis use potassium ions to electrically communicate with distant bacteria that are neither part of their community or even the same bacterial type. Think of it like a sort of like a marketing campaign to attract new community members.
By growing a B. subtilis biofilm within a specialized chamber, the research team was able to identify and document the process by which B. subtilis transmits long-range electrical signals to attract bacteria to the edge of the biofilm. The video below shows what it looks like (the red cells are new to the community).
Jacqueline Humphries, researcher and graduate student in the Division of Biological Sciences, said in a UC San Diego press release:
Our study shows that bacteria living in biofilm communities do something similar to sending electronic messages to friends. In fact, the mechanism we discovered is general. We found that bacteria from one species can send long-range electrical signals that will lead to the recruitment of new members from another species. As a result, we've identified a new mechanism and paradigm for inter-species signaling.
As other research teams work to develop biofilm-resistant surfaces, and chemicals and processes to penetrate the biofilm barrier, study lead Gürol Süel, of the Division of Biological Sciences at UCSD, San Diego Center for Systems Biology, and Howard Hughes Medical Institute, suggests:
[M]ixed species bacterial communities, such as our gut microbiome, could be regulated through electrical signaling. Our work may in the future even lead to new electrical-based biomedical approaches to control bacterial behavior and communities.
Within and around us, bacteria build and protect their communities, and apparently advertise available real estate to passerby. Whether you notice biofilm on your teeth, in your tub, or at the root of a devastating chronic infection—the signal is being sent, "bacteria here."