Bacterial species have diverse cell shapes that enable motility, colonization and virulence. The cell wall defines bacterial shape and is primarily built by two cytoskeleton-guided synthesis machines, the elongasome and the divisome. However, the mechanisms producing complex shapes, like the curved-rod shape of Vibrio cholerae, are incompletely defined. Previous studies have reported that species-specific regulation of cytoskeleton-guided machines enables formation of complex bacterial shapes such as cell curvature and cellular appendages. In contrast, we report that CrvA and CrvB are sufficient to induce complex cell shape autonomously of the cytoskeleton in V. cholerae. The autonomy of the CrvAB module also enables it to induce curvature in the Gram-negative species Escherichia coli, Pseudomonas aeruginosa, Caulobacter crescentus and Agrobacterium tumefaciens. Using inducible gene expression, quantitative microscopy and biochemistry, we show that CrvA and CrvB circumvent the need for patterning via cytoskeletal elements by regulating each other to form an asymmetrically localized, periplasmic structure that binds directly to the cell wall. The assembly and disassembly of this periplasmic structure enables dynamic changes in cell shape. Bioinformatics indicate that CrvA and CrvB may have diverged from a single ancestral hybrid protein. Using fusion experiments in V. cholerae, we find that a synthetic CrvA/B hybrid protein is sufficient to induce curvature on its own, but that expression of two distinct proteins, CrvA and CrvB, promotes more rapid curvature induction. We conclude that morphological complexity can arise independently of cell-shape specification by the core cytoskeleton-guided synthesis machines.

细菌物种具有不同的细胞形状，可实现运动、定植和毒力。细胞壁定义了细菌的形状，主要由两个细胞骨架引导的合成机器构成，即细长体和分裂体。然而，产生复杂形状的机制，如霍乱弧菌的曲杆形状，尚未完全确定。以前的研究报告说，细胞骨架引导机器的物种特异性调节能够形成复杂的细菌形状，例如细胞曲率和细胞附属物。相比之下，我们报告说，CrvA 和 CrvB 足以在霍乱弧菌的细胞骨架中自主诱导复杂的细胞形状。CrvAB 模块的自主性还使其能够在革兰氏阴性菌中诱导弯曲大肠杆菌、铜绿假单胞菌、新月茎杆菌和根癌农杆菌。使用诱导基因表达、定量显微镜和生物化学，我们表明 CrvA 和 CrvB 通过相互调节形成不对称定位的周质结构，直接与细胞壁结合，从而规避了通过细胞骨架元件进行图案化的需要。这种周质结构的组装和拆卸使细胞形状发生动态变化。生物信息学表明，CrvA 和 CrvB 可能已经从一个单一的祖先杂交蛋白中分化出来。在霍乱弧菌中使用融合实验，我们发现合成的 CrvA/B 杂合蛋白本身就足以诱导曲率，但两种不同蛋白质 CrvA 和 CrvB 的表达促进了更快速的曲率诱导。我们得出结论，形态复杂性可以独立于核心细胞骨架引导合成机器的细胞形状规范而产生。