How Do Bacteria Recognize Their Environment? The Role of a Histidine Kinase in Initiating a Biofilm Program

Many bacteria form complex multicellular communities known as biofilms. While biofilms are a common cause of human infections, they can also have productive roles in ecology and agricultural settings. In contrast to the importance of these communities, less is known about how bacteria interpret and respond to environmental cues to form a biofilm. To help understand how bacteria recognize chemical signals from their environment, we studied the soil-dwelling bacteria Bacillus subtilis, which is known to form beneficial biofilms on plant roots. We find extracts from many plant samples can stimulate B. subtilis biofilm formation. One protein that is likely important for the recognition of plant signals is a histidine kinase called KinD. KinD is known to have a role in biofilm formation and also to bind the molecule pyruvate. We find there are varying pyruvate concentrations in our different biofilm-stimulating plant samples. Using transcriptional reporters of biofilm genes, we show that the binding of pyruvate to KinD can initiate the primary biofilm pathway of B. subtilis. However, the addition of pyruvate to bacterial cultures is not sufficient to trigger a biofilm phenotype. This research suggests that the binding of pyruvate to KinD is one of several signals that initiate the formation of a robust biofilm.