Department of Biology, Indiana University, Bloomington Indiana, USA.
Department of Biology, Indiana University, Bloomington Indiana, USA
J Bacteriol. 2021 Apr 21;203(10). doi: 10.1128/JB.00029-21.
Lytic enzymes play an essential role in the remodeling of bacterial peptidoglycan (PG), an extracellular mesh-like structure that retains the membrane in the context of high internal osmotic pressure. Peptidoglycan must be unfailingly stable to preserve cell integrity, but must also be dynamically remodeled for the cell to grow, divide, and insert macromolecular machines. The flagellum is one such macromolecular machine that transits the PG, and flagellar insertion is aided by localized activity of a dedicated PG lyase in Gram-negative bacteria. To date, there is no known dedicated lyase in Gram-positive bacteria for the insertion of flagella. Here, we take a reverse-genetic candidate-gene approach and find that cells mutated for the lytic transglycosylase CwlQ exhibit a severe defect in flagellum-dependent swarming motility. We further show that CwlQ is expressed by the motility sigma factor SigD and is secreted by the type III secretion system housed inside the flagellum. Nonetheless, cells with mutations of CwlQ remain proficient for flagellar biosynthesis even when mutated in combination with four other lyases related to motility (LytC, LytD, LytF, and CwlO). The PG lyase (or lyases) essential for flagellar synthesis in , if any, remains unknown. Bacteria are surrounded by a wall of peptidoglycan and early work in was the first to suggest that bacteria needed to enzymatically remodel the wall to permit insertion of the flagellum. No PG remodeling enzyme alone or in combination, however, has been found to be essential for flagellar assembly in Here, we take a reverse-genetic candidate-gene approach and find that the PG lytic transglycosylase CwlQ is required for swarming motility. Subsequent characterization determined that while CwlQ was coexpressed with motility genes and is secreted by the flagellar secretion apparatus, it was not required for flagellar synthesis. The PG lyase needed for flagellar assembly in remains unknown.
溶菌酶在细菌肽聚糖（PG）的重塑中起着至关重要的作用，肽聚糖是一种细胞外的网状结构，在高内部渗透压的情况下保持细胞膜的稳定。肽聚糖必须保持稳定以维持细胞完整性，但也必须进行动态重塑，以使细胞生长、分裂和插入大分子机器。鞭毛就是这样一种大分子机器，它穿过 PG，鞭毛的插入依赖于革兰氏阴性菌中一种专门的 PG 溶菌酶的局部活性。迄今为止，在革兰氏阳性菌中还没有发现专门用于插入鞭毛的溶菌酶。在这里，我们采用反向遗传候选基因方法，发现溶菌酶转糖基酶 CwlQ 突变的细胞在依赖于鞭毛的群集运动中表现出严重缺陷。我们进一步表明，CwlQ 由运动 sigma 因子 SigD 表达，并由鞭毛内的 III 型分泌系统分泌。尽管如此，即使在与其他四种与运动相关的溶菌酶（LytC、LytD、LytF 和 CwlO）突变组合时，CwlQ 突变的细胞仍然能够有效地合成鞭毛。在 中，对于鞭毛合成至关重要的 PG 溶菌酶（或溶菌酶）仍然未知。细菌被肽聚糖细胞壁包围，早期的 工作首次表明，细菌需要通过酶促重塑细胞壁来允许鞭毛插入。然而，还没有发现单独或组合使用任何 PG 重塑酶对于 中的鞭毛组装是必需的。在这里，我们采用反向遗传候选基因方法，发现 PG 溶菌酶转糖基酶 CwlQ 是群集运动所必需的。随后的表征确定，尽管 CwlQ 与运动基因共表达并由鞭毛分泌装置分泌，但它不是鞭毛合成所必需的。在 中，用于鞭毛组装的 PG 溶菌酶仍然未知。
