Load- and polysaccharide-dependent activation of the Na+-type MotPS stator in the Bacillus subtilis flagellar motor

Abstract

The flagellar motor of Bacillus subtilis possesses two distinct H+-type MotAB and Na+-type MotPS stators. In contrast to the MotAB motor, the MotPS motor functions efficiently at elevated viscosity in the presence of 200 mM NaCl. Here, we analyzed the torque-speed relationship of the Bacillus MotAB and MotPS motors over a wide range of external loads. The stall torque of the MotAB and MotPS motors at high load was about 2,200 pN nm and 220 pN nm, respectively. The number of active stators in the MotAB and MotPS motors was estimated to be about ten and one, respectively. However, the number of functional stators in the MotPS motor was increased up to ten with an increase in the concentration of a polysaccharide, Ficoll 400, as well as in the load. The maximum speeds of the MotAB and MotPS motors at low load were about 200 Hz and 50 Hz, respectively, indicating that the rate of the torque-generation cycle of the MotPS motor is 4-fold slower than that of the MotAB motor. Domain exchange experiments showed that the C-terminal periplasmic domain of MotS directly controls the assembly and disassembly dynamics of the MotPS stator in a load- and polysaccharide-dependent manner.

Autonomous control mechanism of stator assembly in the bacterial flagellar motor in response to changes in the environment

“…These results indicate that Ficoll 400 stabilizes the anchoring of MotS C-PGB to the rigid PG layer in a concentration-dependent manner (Terahara et al, 2017b). Interestingly, torque drastically dropped off by a slight decrease in external load even when the Ficoll 400 concentration is essentially the same, suggesting that the MotPS complex detects changes in both external load and polysaccharide concentration in the environment (Terahara et al, 2017b). The MotPS complex is involved in biofilm formation by B. subtilis cells (Ito et al, 2004).…”

“…This raises the possibility that the MotPS complex may also serve as a viscosity sensor. Rotation measurements of the MotPS-driven motor over a wide range of external load have shown that torque produced by the MotPS motor is much larger in the presence of Ficoll 400, which is a neutral, highly branched, hydrophilic polysaccharide, than in its absence even under the same load condition and that the number of active stator units in the MotPS-driven motor increases from one up to ten with an increase in the Ficoll 400 concentration (Terahara et al, 2017b). The MotPS complex dissociates from and associates with Fig.…”

“…The MotPS complex of B. subtilis acts not only as a Na + sensor but also as a viscosity sensor (Terahara et al, 2017a;2017b). The assembly of the MotPS complex into the motor proceeds through a Na + -induced folding transition of MotS C-PGB (Terahara et al, 2017a).…”

“…The assembly of the MotPS complex into the motor proceeds through a Na + -induced folding transition of MotS C-PGB (Terahara et al, 2017a). Polysaccharides also considerably stabilize the anchoring of MotS C-PGB to the PG layer in a load-dependent manner, thereby increasing the number of active MotPS stator units in the motor from one to ten (Terahara et al, 2017b). However, it remains unknown how MotS C-PGB senses Na + and polysaccharides, how Na + induces the folding transition of MotS C-PGB , and how polysaccharides stabilize the association of MotS C-PGB with the PG layer.…”

“…The ion channel complex dynamically assembles into and disassembles from the rotor during motor rotation (Leake et al ., ), indicating that the stator units are not permanently fixed in place around the rotor. Interestingly, the flagellar motor autonomously controls the assembly of stator units in the motor in response to changes in the environment (Fukuoka et al ., ; Lele et al ., ; Tipping et al ., ; Sowa et al ., ; Paulick et al ., ; Terahara et al ., ; ). Thus, the ion channel complex by itself also acts as a biosensor to detect changes in the environment.…”