Team:Grenoble-Alpes/phage lysis
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DNA EXTRACTION
The first main step in our system is the lysis of bacteria by bacteriophages. This step is decisive for all the rest of the system. In fact this step allows the release of DNA in the medium by lysing the specific bacteria. It is this specific DNA that will be extracted, digested and detected by our plasmid probes. So if the DNA released hybridize to the probes, it gives two essential information:
- Which bacterial species are present in the patient sample.
- What are the best bacteriophages capable of infecting this bacteria, and thus, treating the patient.
About bacteriophages
But to understand a little more this last point, let’s mention what is a bacteriophage and how it infects bacteria: Bacteriophages, also called phages, are bacteria-specific viruses: each bacteriophage is able to infect one or more bacterial strains from a single bacterial species. This specificity is characterized by differences in infection and replication efficiency. This last feature is proportional to the number of lysed bacteria and therefore to the amount of DNA released which will be able to hybridize with the probes. That is how, after the transformation step, we will be able to determine the lysis efficiency by following the fluorescence rate measured by our system. Then we will be able to choose the best bacterium killer bacteriophage.
However, be careful: some bacteriophages are not just able to lyse bacteria. Indeed, as you see in Figure 1, two types of infection cycles are distinguished:
1) Lytic cycle: the bacteriophage, once inside the bacterial host, uses the machinery of the infected cell to replicate, releasing a great number of new virions after a bacterial burst (in red in Figure 1).
2) Lysogenic cycle: the bacteriophage, once inside the bacterial host, integrates its DNA to the host DNA and becomes a prophage able to transmit itself to the descendants (in blue in Figure 1).
About bacteriophages
Lytic bacteriophages, as their name suggests, destroy the bacteria. They divert the bacterial machinery to their advantage to reproduce and multiply.
Indeed, bacteriophages, unable to reproduce by their own means, inject their genetic material into host bacteria (red 1. in Figure 1). Thanks to the enzymes and ribosomes of the host, the viral genome can be replicated and translated to form many copies (red 3. in Fig. 1). At the end of the process, the bacteria burst and dozens or even hundreds new bacteriophages - identical to the original - are released in the medium and therefore available to attack other bacteria of the same species (red 4. in the Fig. 1). True “professional killers”, lytic bacteriophages are the natural predators of bacteria. It is precisely these lytic bacteriophages that are used for therapeutic purposes to fight against bacterial infections (bacteriophage therapy). For example, in Russia, bacteriophages are used to treat foot infections in patients with type 2 diabetes, known as diabetic foot ulcers and may cause amputation ; as described in the scientific article Bacteriophage Treatment of Infected Diabetic Foot Ulcers by scientists of the Institute of Chemical Biology and Fundamental Medicine SB RAS, Laboratory of Molecular Microbiology, Novosibirsk, Russian Federation. Thereby, we also use lytic bacteriophages in our system.