Mycoplasmas are very simple bacteria. Mycoplasma agalactiae is one of the most important pathogenic mycoplasma species in sheep and goats. By specifically inactivating a certain area in the genome of this pathogen the scientists made an important step forward, especially due to the fact that mycoplasmas are generally difficult to manipulate genetically .
They were able to use these so-called knock-out mutants to explore for the first time those mechanisms used by the mycoplasmas to outsmart the immune defenses during an infection in a natural host organism. The mycoplasmas were found to be such clever "genomic strategists" that they could even compensate for the artificial gene inactivation.
Surface variation as a strategy against immune response
The genes are therefore subject to phase variation, which means that they can be spontaneously switched on and off at high frequency and replaced by other variants. Through this surface variation, the mycoplasmas are equipped with a sort of molecular stealth mechanism that can outsmart the immune system.
The scientists identified an important component of this mechanism, an enzyme called recombinase , and were able to deactivate it through genetic modification. The laboratory-produced mycoplasmas, called phase-locked mutants, were tested for the first time in vivo, namely in sheep, the natural host. Surprisingly, the mycoplasmas proved to be real survivors once they were back in their natural environment.
Even an artificially inactivated molecular stealth mechanism can not stop the mycoplasmas' survival abilities
Although the phase-locked mutants should not have been able to escape the immune defenses of the infected animals, there were no differences in the course of the disease with unaltered mycoplasmas. Even without an active recombinase, the mycoplasma mutants demonstrably varied their surface proteins by using a previous unknown alternative mechanism, which could only be discovered and deciphered by the in vivo experiments.
"The research findings regarding the effective infection of a natural host confirm that the switching of its surface protein antigens is absolutely necessary for the survival of Mycoplasma agalactiae during an infection," says Chopra-Dewasthaly. "That this was possible without the important recombination shows how cleverly mycoplasmas use their gene repertoire to resist the host's immune defense.
Rosengarten explains the difference between the laboratory and in vivo experiments by pointing to the different environmental conditions which the mycoplasmas are subjected to: "In the test tube, the mycoplasmas can propagate under ideal conditions and do not have to expect an immune response. means that there is no immediate need to respond to the inactivation of the phase variation . "
In an infected host organism, on the other hand, the mycoplasmas as pathogens must become active immediately once they are recognized and attacked by the immune system if they want to survive. The fact that pathogenic mycoplasmas can indeed compensate for the confirmed and perfectly reproducible inactivation of the phase variation in their natural environment in a host organism and how this is done can only be detected and analyzed in a living animal.