Departments of Biochemistry, Stanford University School of Medicine, Stanford, California 94305, USA.
J Bacteriol. 2011 Nov;193(21):5898-904. doi: 10.1128/JB.00168-11. Epub 2011 Aug 19.
The principal social activity of Myxococcus xanthus is to organize a dynamic multicellular structure, known as a swarm. Although its cell density is high, the swarm can grow and expand rapidly. Within the swarm, the individual rod-shaped cells are constantly moving, transiently interacting with one another, and independently reversing their gliding direction. Periodic reversal is, in fact, essential for creating a swarm, and the reversal frequency controls the rate of swarm expansion. Chemotaxis toward nutrient has been thought to drive swarming, but here the nature of swarm growth and the impact of genetic deletions of members of the Frz family of proteins suggest otherwise. We find that three cytoplasmic Frz proteins, FrzCD, FrzF, and FrzE, constitute a cyclic pathway that sets the reversal frequency. Within each cell these three proteins appear to be connected in a negative-feedback loop that produces oscillations whose frequencies are finely tuned by methylation and by phosphorylation. This oscillator, in turn, drives MglAB, a small G-protein switch, to oscillate between its GTP- and GDP-bound states that ultimately determine when the cell moves forward or backward. The periodic reversal of interacting rod-shaped cells promotes their alignment. Swarm organization ensures that each cell can move without blocking the movement of others.
粘细菌的主要社会活动是组织一个动态的多细胞结构，称为群集。尽管其细胞密度很高，但群集可以快速生长和扩展。在群集中，个体杆状细胞不断移动，短暂地相互作用，并独立地反转它们的滑行方向。周期性反转实际上对于创建群集是必不可少的，反转频率控制着群集扩展的速度。趋化作用被认为是驱动群集的原因，但这里群集生长的性质和 Frz 家族蛋白成员的遗传缺失的影响表明并非如此。我们发现三种细胞质 Frz 蛋白（FrzCD、FrzF 和 FrzE）构成了一个循环途径，设定了反转频率。在每个细胞中，这三种蛋白质似乎连接在一个负反馈环中，产生的振荡频率由甲基化和磷酸化精细调节。这个振荡器反过来又驱动 MglAB，一种小 G 蛋白开关，在其 GTP 和 GDP 结合状态之间振荡，最终决定细胞向前还是向后移动。相互作用的杆状细胞的周期性反转促进了它们的对齐。群集组织确保每个细胞都可以移动而不会阻碍其他细胞的移动。
