Understanding the Role of Peptidoglycan Metabolism in Bacterial Predation

我们正在研究一种天然的、友好的细菌噬菌蛭弧菌（Bdellovibrio bacteriovorus）--大致翻译为“水蛭般的食菌者”--它能够杀死其他不那么友好的细菌。控制细菌种群在人类生存的许多领域都很重要-即在医疗保健中解决不需要的致病物种（例如超级细菌），作物瘟疫，食品安全，生物污垢和水质管理。存在使用i）从蛭弧菌研究中获得的知识，ii）蛋白质产品（酶制剂）或iii）以治疗方式的全细胞/培养物的潜力。与其他捕食性细菌不同，蛭弧菌从内部杀死目标-进入它们，分解它们，在内部繁殖，然后破裂它们释放子细胞，开始新的循环。蛭弧菌起源于非捕食性的祖先细菌，因此发展了特殊的工具，使其能够进入并杀死其他细菌。这些工具是蛋白酶-我们的目标是研究这些酶的形式和功能，以便我们更好地了解杀灭过程，甚至可能提高蛭弧菌作为抗菌剂的潜力。这些蛋白质可以非常有用，让我们靶向病原体细胞的入侵，并打破他们在一个可控的方式。我们的实验室先前的调查显示，这样的酶（Bd 3459）是针对猎物，并采取行动，以改变猎物的形状。我们发现，Bd 3459通过切割猎物壁的特定区域（称为肽聚糖）来实现这一点，导致壁部分塌陷，从而改变了它以前支持的细菌的形状-就像锯掉房子的支撑墙一样！形状的变化为蛭弧菌入侵猎物提供了最佳空间，这也向其他入侵者发出信号，表明这个特定的“家”已经被占领，进一步进入将是浪费。蛭弧菌还有更多的“特殊”酶，它们可以“切掉”细菌猎物的细胞壁--我们希望对这些酶进行研究，以更全面地了解蛭弧菌开始杀死猎物时发生的情况，并允许人们将这些酶用于生物技术。（被称为X射线晶体学），使用荧光版本的酶来跟踪它们发挥作用的位置（它们是“咀嚼”宿主还是防止不必要的自我破坏？），监测功能的精确性质（称为酶测定），并通过构建细菌的突变菌株（缺乏酶）来测试酶：位置：功能关系，以确认/消除所产生的假设。肽聚糖靶向酶的研究具有非常实际的应用-完整的壁对于大多数医学相关的细菌是必不可少的，并且形成了几种非常成功的抗生素（例如青霉素，万古霉素）的作用基础。我们的研究结果可能会为这一过程提供信息，并对微生物生理学（形式和功能）产生影响。

We are studying the natural, friendly bacterium Bdellovibrio bacteriovorus - roughly translated as "leech-like bacteria-eater" - which is able to kill other less-friendly bacteria. The control of bacterial populations is important in many areas of human existence - namely tackling undesirable pathogenic species in healthcare (e.g. superbugs), crop pestilence, food safety, biofouling and water quality management. The potential exists to use i)knowledge gained from Bdellovibrio study, ii)protein products (enzybiotics) or iii)whole cells/cultures in a therapeutic manner. Unlike other predatory bacteria, Bdellovibrio kills its targets from within - entering them, breaking them down, reproducing inside and then bursting them to release daughter cells and begin the cycle anew.Bdellovibrio arose from a non-predatory ancestor bacterium, and thus developed specialized tools that allow it to enter and kill other bacteria. These tools are protein enzymes - we aim to investigate the form and function of these so that we understand the killing process better, and perhaps even enhance the potential of Bdellovibrio as an antibacterial agent. Such proteins can be very useful to let us target the invasion of pathogen cells and break them in a controlled way.Prior investigation by our laboratories revealed that one such enzyme (Bd3459) was targeted to the prey, and acted to change prey shape. We showed that Bd3459 achieved this by cutting particular regions of the prey wall (known as peptidoglycan), causing the wall to partially collapse and so alter the shape of the bacterium that it previously supported - much like sawing away at the support walls of a house! The shape change serves to provide the optimal space for Bdellovibrio invasion of prey, which also signals to fellow invaders that this particular "home" is occupied and that further entry would be wasteful. There are more "special" Bdellovibrio enzymes that "chip away" at the cell walls of bacterial prey- we would like to work on these to develop a fuller picture of what goes on when Bdellovibrio starts to kill its prey and to allow people to use these for biotechnology.We will look at the enzymes themselves in atomic detail (known as x-ray crystallography), using fluorescent versions of the enzymes to track where they exert their effects (do they "chew up" the host or prevent unwanted destruction of self?), monitoring the precise nature of the function (known as enzyme assays), and also testing the enzyme:location:function relationship by constructing mutant strains of bacteria (lacking the enzymes) to confirm/dispel the hypotheses arising.The investigation of peptidoglycan-targeting enzymes has a very practical application - an intact wall is essential to most medically-relevant bacteria, and forms the basis of action of several very successful antibiotics (e.g. penicillin, vancomycin). Results from our study may inform on this process, and also have implications for microbial physiology (form and function) in general.