Study describes the mechanisms that enable bacteria to adapt to varying viscosities in their environment
In a new study, published in the journal Nature Communications, researchers at Texas A&M University have found that the appendages controlling bacterial navigation, called the flagella, adjust to changes in the viscosity of fluids very precisely. This adaptation enables the bacterium to continue using its flagella to search for nutrients, sense surfaces and establish colonies in different habitats.
“There is a significant interest in the biomedical fields to understand how individual bacterial cells transition from a lonesome existence to a community lifestyle,” said Pushkar Lele, associate professor in the Artie McFerrin Department of Chemical Engineering. Recent evidence suggests that the flagellum plays a role in sensing changes in the cell’s mechanical environment — a process called mechanosensing. So, if the bacterium encounters an increase in resistance to the rotation of its flagella, it would be sensed as an increase in the viscosity of the environment. In response, the flagellar motor recruit extra stator units to compensate by developing more power. However, research has also shown that such an increase in the resistance prevents the flagellum from switching directions of rotation, potentially rendering the chemotaxis machinery defunct.
For their experiments, the researchers chose a strain of E. coli with a fluorescently-labeled chemotaxis protein, CheY-P, that binds to the flagellar motor to initiate flagellar switching. The researchers applied resistance to the motor and then observed the level of fluorescence using high-powered microscopes. They found that the fluorescence dropped below baseline when they removed the stator proteins using genetic techniques. In comparison, the fluorescence level remained at the baseline when the stators continually delivered torque to rotate the motor. This suggested that the presence of the stator units promoted CheY-P binding to the motor. Based on these observations, the team theorized that in high viscosity environments, the increase in mechanical torque provided by the extra stator units increases the binding of CheY-P to the motor, thereby maintaining homeostasis in the switching function of the flagellum. Lele points out this phenomenon of fine-tuning the internal state to adapt to changing mechanical loads bears a crude resemblance to proprioceptive adaptation, whereby organisms with a nervous system continuously intuit their position and velocity to make adaptive changes to achieve homeostasis or a stable physiological state. For example, insects’ muscular skeletal systems internally adapt and adjust to varying loads on their limbs to maintain their posture and grip when walking on the floor or the ceiling.
Source: Texas A&M University news release
