Department of Plant Pathology and MOA Key Laboratory of Pest Monitoring and Green Management, College of Plant Protection, Beijing Key Laboratory of Seed Disease Testing and Control, China Agricultural Universitygrid.22935.3f, Beijing, People's Republic of China.
Key Laboratory of Integrated Crop Pest Management of Anhui Province, Key Laboratory of Biology and Sustainable Management of Plant Diseases and Pests of Anhui Higher Education Institutes, School of Plant Protection, Anhui Agricultural Universitygrid.411389.6, Hefei, People's Republic of China.
Microbiol Spectr. 2022 Oct 26;10(5):e0181622. doi: 10.1128/spectrum.01816-22. Epub 2022 Aug 30.
The cell wall peptidoglycan of bacteria is essential for their survival and shape development. The penicillin-binding proteins (PBPs) are responsible for the terminal stage of peptidoglycan assembly. It has been shown that PBPC, a member of class A high-molecular-weight PBP, played an important role in morphology maintenance and stress response in Clavibacter michiganensis. Here, we reported the stress response strategies under viable but nonculturable (VBNC) state and revealed the regulation of peptidoglycan assembly by PBPC in C. michiganensis cells. Using atomic force microscopy imaging, we found that peptidoglycan of C. michiganensis cells displayed a relatively smooth and dense surface, whereas was characterized by a "ridge-and-groove" surface, which was more distinctive after Cu treatment. The peptidoglycan layer of wild type cells exhibited a significant increase in thickness and slight increase in cross-linkage following Cu treatment. Compared with wild type, the thickness and cross-linkage of peptidoglycan decreased during log phase in cells, but the peptidoglycan cross-linkage increased significantly under Cu stress, while the thickness did not change. It is noteworthy that the above changes in the peptidoglycan layer resulted in a significant increase in the accumulation of amylase and exopolysaccharide in . This study elucidates the role of PBPC in Gram-positive rod-shaped plant pathogenic bacterium in response to environmental stimuli by regulating the assembling of cell wall peptidoglycan, which is significant in understanding the survival of C. michiganensis under stress and the field epidemiology of tomato bacterial canker disease. Peptidoglycan of cell walls in bacteria is a cross-linked and meshlike scaffold that provides strength to withstand the external pressure. The increased cross-linkage in peptidoglycan and altered structure in VBNC cells endowed the cell wall more resistant to adversities. Here we systematically evaluated the stress response strategies in Gram-positive rod-shaped bacterium C. michiganensis log phase cells and revealed a significant increase of peptidoglycan thickness and slight increase of cross-linkage after Cu treatment. Most strikingly, knocking-out of PBPC leads to a significant increase in cross-linking of peptidoglycan in response to Cu treatment. Understanding the stress resistance mechanism and survival strategy of phytopathogenic bacteria is the basis of exploring bacterial physiology and disease epidemiology.
细菌细胞壁的肽聚糖对于它们的生存和形态发育至关重要。青霉素结合蛋白（PBPs）负责肽聚糖组装的终末阶段。已经表明，属于 A 类高分子量 PBP 的 PBPC 在 Clavibacter michiganensis 的形态维持和应激反应中发挥重要作用。在这里，我们报告了在存活但非可培养（VBNC）状态下的应激反应策略，并揭示了 PBPC 在 C. michiganensis 细胞中对肽聚糖组装的调节。使用原子力显微镜成像，我们发现 C. michiganensis 细胞的肽聚糖表面相对光滑且密集，而 则表现出“脊和槽”表面，经 Cu 处理后更为明显。与野生型相比，Cu 处理后野生型细胞的肽聚糖层厚度显著增加，交联度略有增加。与野生型相比，在 细胞的对数生长期，肽聚糖的厚度和交联度降低，但在 Cu 胁迫下，肽聚糖的交联度显著增加，而厚度没有变化。值得注意的是，肽聚糖层的上述变化导致 在 中的淀粉酶和胞外多糖积累显著增加。这项研究通过调节细胞壁肽聚糖的组装阐明了 PBPC 在革兰氏阳性杆状植物病原细菌应对环境刺激中的作用，这对于理解 C. michiganensis 在应激下的存活以及番茄细菌性溃疡病的田间流行病学具有重要意义。 细菌细胞壁的肽聚糖是一种交联的网格状支架，为细胞壁提供了承受外部压力的强度。VBNC 细胞中肽聚糖的交联增加和结构改变使细胞壁更能抵抗逆境。在这里，我们系统地评估了革兰氏阳性杆状细菌 C. michiganensis 对数生长期细胞的应激反应策略，并发现 Cu 处理后肽聚糖的厚度显著增加，交联度略有增加。最引人注目的是，敲除 PBPC 导致 Cu 处理时肽聚糖的交联显著增加。了解植物病原细菌的抗逆机制和生存策略是探索细菌生理学和疾病流行病学的基础。
