Secretion, mode of action and utilisation of a new anti-bacterial toxin

蛋白质分泌系统在细菌病原体的毒力、宿主相互作用和竞争性生存中起着核心作用。它们是一种专门的机器，用于将特定的蛋白质转移出细菌细胞，要么转移到环境中，要么直接注射到目标细胞中。VI型分泌系统(T6SS)是一个广泛存在且最近才被确认的例子。越来越明显的是，这种T6SS在各种革兰氏阴性菌的毒力和竞争力中发挥着关键作用，包括重要的人类、动物和植物病原体。病原体可以利用T6SS直接靶向真核生物，作为经典的毒力因子。或者，许多病原体可以使用T6SS来靶向其他细菌细胞，杀死或抑制竞争对手。因此，“抗菌”T6SS提供了一种竞争机制，允许病原体在多菌感染部位或环境宿主中繁殖，最终导致疾病。抗菌T6SS将有毒蛋白质输送到目标细菌细胞中，有效地杀死它们或抑制它们的生长。最近该领域的工作，包括我们实验室的工作，表明不同的T6SS分泌多种不同的新型抗菌毒素。虽然到目前为止已经有几个大类的功能特征，特别是附着在细菌细胞壁或细胞膜上的酶毒素，但许多其他毒素似乎与已知的蛋白质无关。我们已经确定了新的T6SS分泌的抗菌毒素，这些毒素不属于前面描述的任何类别。因此，它们在敏感细胞中的作用模式和细胞靶点尚不清楚。本博士项目的重点将是研究其中一种新毒素，以确定其毒性模式、分泌途径、敏感细胞中的细胞靶点以及目标细胞发挥其作用所需的任何细胞功能。此外，还将研究分泌细胞如何对毒素产生自身抵抗力或“免疫力”，以及相关毒素在不同生物体中的分布。发现新的抗细菌毒素的脆弱细胞靶点非常重要，因为它们可能揭示抗生素或其他药物设计的新靶点。这些毒素也可能是了解基本细菌生理学或具有生物技术实用价值的宝贵研究工具。

Protein secretion systems play a central role in the virulence, host interaction and competitive survival of bacterial pathogens. They are specialised machines used to translocate specific proteins out of the bacterial cell, either to the environment or injected directly into target cells. A widespread and relatively recently-identified example is the Type VI secretion system (T6SS). It is becoming increasingly apparent that this T6SS plays a key role in the virulence and competitiveness of diverse Gram-negative bacteria, including important human, animal and plant pathogens. Pathogens can use T6SSs to directly target eukaryotic organisms, as classical virulence factors. Alternatively, many pathogens can use T6SSs to target other bacterial cells, killing or inhibiting rivals. 'Anti-bacterial' T6SSs thus provide a competitive mechanism to allow pathogens to proliferate in polymicrobial infection sites or environmental reservoirs and ultimately cause disease. Anti-bacterial T6SSs deliver toxic proteins into target bacterial cells, efficiently killing them or inhibiting their growth. Recent work in the field, including from our lab, suggests that different T6SSs secrete multiple, diverse and novel anti-bacterial toxins. Whilst several broad classes have been functionally characterised to date, particularly enzymic toxins attaching the bacterial cell wall or cell membrane, many other toxins appear unrelated to known proteins. We have identified new T6SS-secreted anti-bacterial toxins which do not fall into any of the previously described classes. Therefore their mode of action and cellular target in susceptible cells is unknown. The focus of this PhD project will be to study one of these new toxins in order to determine its mode of toxicity, pathway of secretion, cellular target in susceptible cells and any cellular functions of the target cell which are required in order for the toxin to exert its effect. How self-resistance or 'immunity' to the toxin in the secreting cell is achieved will also be examined, as will the distribution of related toxins in different organisms. It is important to discover the vulnerable cellular targets of new anti-bacterial toxins since they may reveal new targets for antibiotic or other drug design. The toxins may also represent valuable research tools to understand basic bacterial physiology or have biotechnological utility.