Kawai Yoshikazu, Errington Jeff
Centre for Bacterial Cell Biology, Biosciences Institute, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom.
Front Microbiol. 2023 Jun 2;14:1204979. doi: 10.3389/fmicb.2023.1204979. eCollection 2023.
Bacterial cells are surrounded by a peptidoglycan (PG) wall, which is a crucial target for antibiotics. It is well known that treatment with cell wall-active antibiotics occasionally converts bacteria to a non-walled "L-form" state that requires the loss of cell wall integrity. L-forms may have an important role in antibiotic resistance and recurrent infection. Recent work has revealed that inhibition of PG precursor synthesis efficiently induces the L-form conversion in a wide range of bacteria, but the molecular mechanisms remain poorly understood. Growth of walled bacteria requires the orderly expansion of the PG layer, which involves the concerted action not just of synthases but also degradative enzymes called autolysins. Most rod-shaped bacteria have two complementary systems for PG insertion, the Rod and aPBP systems. has two major autolysins, called LytE and CwlO, which are thought to have partially redundant functions. We have dissected the functions of autolysins, relative to the Rod and aPBP systems, during the switch to L-form state. Our results suggest that when PG precursor synthesis is inhibited, residual PG synthesis occurs specifically the aPBP pathway, and that this is required for continued autolytic activity by LytE/CwlO, resulting in cell bulging and efficient L-form emergence. The failure of L-form generation in cells lacking aPBPs was rescued by enhancing the Rod system and in this case, emergence specifically required LytE but was not associated with cell bulging. Our results suggest that two distinct pathways of L-form emergence exist depending on whether PG synthesis is being supported by the aPBP or RodA PG synthases. This work provides new insights into mechanisms of L-form generation, and specialisation in the roles of essential autolysins in relation to the recently recognised dual PG synthetic systems of bacteria.
细菌细胞被肽聚糖（PG）壁包围，肽聚糖壁是抗生素的关键作用靶点。众所周知，用细胞壁活性抗生素治疗有时会使细菌转变为无壁的“L型”状态，这需要细胞壁完整性的丧失。L型细菌可能在抗生素耐药性和复发性感染中起重要作用。最近的研究表明，抑制PG前体合成可有效诱导多种细菌发生L型转变，但其分子机制仍知之甚少。有壁细菌的生长需要PG层的有序扩展，这不仅涉及合成酶的协同作用，还涉及称为自溶素的降解酶的协同作用。大多数杆状细菌有两个互补的PG插入系统，即Rod和aPBP系统。有两种主要的自溶素，称为LytE和CwlO，它们被认为具有部分冗余功能。我们剖析了自溶素在转变为L型状态过程中相对于Rod和aPBP系统的功能。我们的结果表明，当PG前体合成受到抑制时，残余的PG合成特异性地发生在aPBP途径中，这是LytE/CwlO持续自溶活性所必需的，从而导致细胞膨胀和高效的L型出现。通过增强Rod系统挽救了缺乏aPBPs的细胞中L型生成的失败，在这种情况下，L型出现特别需要LytE，但与细胞膨胀无关。我们的结果表明，根据PG合成是由aPBP还是RodA PG合成酶支持，存在两种不同的L型出现途径。这项工作为L型生成机制以及必需自溶素在与最近认识到的细菌双PG合成系统相关的作用中的特化提供了新的见解。
