Schoof Marion, O'Callaghan Maureen, Hefer Charles, Glare Travis R, Paulson Amber R, Hurst Mark R H
AgResearch, Resilient Agriculture, Lincoln Research Centre, Lincoln, New Zealand.
Wine and Molecular Biosciences Dept, Faculty of Agriculture and Life Sciences, Lincoln University, Lincoln, New Zealand.
Microbiol Spectr. 2023 Mar 23;11(2):e0036423. doi: 10.1128/spectrum.00364-23.
Secretion of exoproteins is a key component of bacterial virulence, and is tightly regulated in response to environmental stimuli and host-dependent signals. The entomopathogenic bacterium Yersinia entomophaga MH96 produces a wide range of exoproteins including its main virulence factor, the 2.46 MDa insecticidal Yen-Tc toxin complex. Previously, a high-throughput transposon-based screening assay identified the region of exoprotein release (YeRER) as essential to exoprotein release in MH96. This study defines the role of the YeRER associated ambiguous holin/endolysin-based lysis cluster (ALC) and the novel RoeA regulator in the regulation and release of exoproteins in MH96. A mutation in the ambiguous lysis cassette (ALC) region abolished exoprotein release and caused cell elongation, a phenotype able to be restored through -complementation with an intact ALC region. Endogenous ALC did not impact cell growth of the wild type, while artificial expression of an optimized ALC caused cell lysis. Using HolA-sfGFP and Rz1-sfGFP reporters, Rz1 expression was observed in all cells while HolA expression was limited to a small proportion of cells, which increased over time. Transcriptomic assessments found expression of the genes encoding the prominent exoproteins, including the Yen-Tc, was reduced in the mutant and identified a 220 ncRNA of the YeRER intergenic region that, when complemented in the wildtype, abolished exoprotein release. A model for mediated exoprotein regulation and release is proposed. While theoretical models exist, there is not yet any empirical data that links ALC phage-like lysis cassettes with the release of large macro-molecular toxin complexes, such as Yen-Tc in Gram-negative bacteria. In this study, we demonstrate that the novel RoeA activates the production of exoproteins (including Yen-Tc) and the ALC at the transcriptional level. The translation of the ALC holin is confined to a subpopulation of cells that then lyse over time, indicative of a complex hierarchical regulatory network. The presence of an orthologous RoeA and a HolA like holin 5' of an eCIS Afp element in Pseudomonas chlororaphis, combined with the presented data, suggests a shared mechanism is required for the release of some large macromolecular protein assemblies, such as the Yen-Tc, and further supports classification of phage-like lysis clusters as type 10 secretion systems.
外蛋白的分泌是细菌毒力的关键组成部分,并且会根据环境刺激和宿主相关信号进行严格调控。昆虫病原菌嗜虫耶尔森氏菌MH96能产生多种外蛋白,包括其主要毒力因子——2.46 MDa的杀虫Yen-Tc毒素复合物。此前,一项基于高通量转座子的筛选试验确定了外蛋白释放区域(YeRER)对MH96中外蛋白的释放至关重要。本研究确定了与YeRER相关的基于模糊性噬菌体整合酶/内溶素的裂解簇(ALC)和新型RoeA调节因子在MH96外蛋白调控和释放中的作用。模糊裂解盒(ALC)区域的突变消除了外蛋白的释放并导致细胞伸长,这种表型可通过完整的ALC区域进行互补恢复。内源性ALC不影响野生型细胞的生长,而人工表达优化后的ALC则会导致细胞裂解。使用HolA-sfGFP和Rz1-sfGFP报告基因,在所有细胞中均观察到Rz1的表达,而HolA的表达仅限于一小部分细胞,且随时间增加。转录组评估发现,在突变体中,编码包括Yen-Tc在内的主要外蛋白的基因表达降低,并鉴定出YeRER基因间区域的一个220 ncRNA,当它在野生型中互补时,会消除外蛋白的释放。提出了一种介导外蛋白调控和释放的模型。虽然存在理论模型,但尚无任何经验数据将ALC类噬菌体裂解盒与革兰氏阴性菌中大分子毒素复合物(如Yen-Tc)的释放联系起来。在本研究中,我们证明新型RoeA在转录水平上激活外蛋白(包括Yen-Tc)和ALC的产生。ALC噬菌体整合酶的翻译局限于一部分细胞亚群,这些细胞随后会随时间裂解,这表明存在一个复杂的分级调控网络。在绿针假单胞菌中,eCIS Afp元件5'端存在直系同源RoeA和类似HolA的噬菌体整合酶,结合本文数据,表明释放某些大分子蛋白组装体(如Yen-Tc)需要一种共同机制,并进一步支持将类噬菌体裂解簇归类为10型分泌系统。