|from Anatomy & Physiology by Phil Schatz|
Enter Bacillus subtilis, a bacterium often used as a model organism for studying biofilms. A biofilm is a collection of bacteria that adhere to each other and, often, a surface. Biofilms are more resistant to antibiotic treatment than free-living bacteria, and can commonly be formed on medical devices, such as catheters. It has been known for many years that bacteria within a biofilm are able to communicate through a process known as quorum sensing, which involves the release of chemicals by the members of the biofilm to control the population density. Recently, a study found that in addition to quorum sensing, B. subtilis cells can communicate through the creation of and propagation of action potentials, similar to neuronal signaling.
It was observed that the entirety of the B. subtilis biofilm would undergo metabolic changes in response to glutamate and ammonium nutrient limitation affecting the cells in the center of the biofilm. In order for these widespread metabolic changes to occur, the cells in the interior of the biofilm must communicate with the cells of the periphery. It was found that an active propagation of a potassium ion signal through the use of potassium channels on the cells was responsible for this communication. As the potassium channels on the surface of the bacteria opened, potassium would rush into the cells from the surrounding environment, resulting in membrane depolarization. The membrane depolarization is linked to a decreased ability of the cells to take up glutamate and ammonium, allowing these nutrients to build up and replenish the supply to the interior cells.
Biofilms are notoriously difficult to treat when they form in patients. As many as 80% of chronic infections are caused by biofilm formation. Persistent staphylococcal infections are often caused by biofilms, as are Pseudomonas aeruginosa lung infections. It is typically the interior cells of the biofilm, which have a more dormant lifestyle, that are most responsible for antibiotic resistance. Learning more about how the biofilms communicate can facilitate improved treatment. If the action potential creation of these bacteria can be inhibited, the cells will be unable to communicate in times of nutrient depletion, leading the cell death at the interior of the biofilm. This could greatly improve the ability to treat these infections, leading to better outcomes for patients. Perhaps some day soon, we will have better tools for treatment to gain ground against these crafty biofilm bacteria.
Beyond the impact of these findings on patients, it is truly marvelous to see what these relatively simple organisms can accomplish. Bacterial cells are almost 1000 times simpler than mammalian cells when genome sizes are compared, yet they are capable of accomplishing signaling akin to the complexity of neuronal signaling. There seems to be no end to the surprises these timeless organisms have in store for us. Who knows what will come to light next.