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).
