Ford Katie M, Antani Jyot D, Nagarajan Aravindh, Johnson Madeline M, Lele Pushkar P
Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX, United States.
Front Microbiol. 2018 Sep 18;9:2197. doi: 10.3389/fmicb.2018.02197. eCollection 2018.
swarm on semi-solid surfaces with the aid of flagella. It has been hypothesized that swarmer cells overcome the increased viscous drag near surfaces by developing higher flagellar thrust and by promoting surface wetness with the aid of a flagellar switch. The switch enables reversals between clockwise (CW) and counterclockwise (CCW) directions of rotation of the flagellar motor. Here, we measured the behavior of flagellar motors in swarmer cells. Results indicated that although the torque was similar to that in planktonic cells, the tendency to rotate CCW was higher in swarmer cells. This suggested that swarmers likely have a smaller pool of phosphorylated CheY. Results further indicated that the upregulation of the flagellin gene was not critical for flagellar thrust or swarming. Consistent with earlier reports, moisture added to the swarm surface restored swarming in a CCW-only mutant, but not in a FliG mutant that rotated motors CW-only (FliG). Fluorescence assays revealed that FliG cells grown on agar surfaces carried fewer flagella than planktonic FliG cells. The surface-dependent reduction in flagella correlated with a reduction in the number of putative flagellar preassemblies. These results hint toward a possibility that the conformational dynamics of switch proteins play a role in the proper assembly of flagellar complexes and flagellar export, thereby aiding bacterial swarming.
借助鞭毛在半固体表面上群体游动。据推测，群体游动细胞通过产生更高的鞭毛推力以及借助鞭毛开关促进表面湿润来克服靠近表面时增加的粘性阻力。该开关能使鞭毛马达在顺时针（CW）和逆时针（CCW）旋转方向之间反转。在此，我们测量了群体游动细胞中鞭毛马达的行为。结果表明，尽管扭矩与浮游细胞中的相似，但群体游动细胞逆时针旋转的倾向更高。这表明群体游动细胞可能具有较少的磷酸化CheY池。结果还进一步表明，鞭毛蛋白基因的上调对鞭毛推力或群体游动并不关键。与早期报告一致，向群体表面添加水分可恢复仅逆时针旋转突变体的群体游动能力，但不能恢复仅使马达顺时针旋转的FliG突变体（FliG）的群体游动能力。荧光测定显示，在琼脂表面生长的FliG细胞比浮游FliG细胞携带的鞭毛更少。表面依赖性的鞭毛减少与假定的鞭毛预组装体数量的减少相关。这些结果暗示，开关蛋白的构象动力学可能在鞭毛复合物的正确组装和鞭毛输出中发挥作用，从而有助于细菌群体游动。
