Understanding the Role of Peptidoglycan Metabolism in Bacterial Predation

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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.