How shaved bacteria escape their host
Credits: Magda Atilano, ITQB/Univ. Oxford
Oeiras, 02.04.2014
Most bacteria maintain their shape through a network of peptidoglycan molecules. While essential, they are also the Achilles’ heel of these bacteria: peptidoglycan is both the target of many currently used antibiotics and the signal the hosts perceive as danger, activating the inflammatory response to eliminate the bacteria. Researchers from the Bacterial Cell Surfaces and Pathogenesis Lab and the Bacterial Cell Biology Lab have uncovered how some bacteria become unrecognizable by the host, resorting to an enzyme that trims exposed peptidoglycan. Results are published this week on eLife, a new open-access journal supported by the Howard Hughes Medical Institute, the Max Planck Society and the Wellcome Trust.
Understanding how bacteria escape detection helps us to fight them, something particularly important when dealing with antibiotic resistant Staphylococcus aureus or Streptococcus pneumoniae, used in this study. Besides uncovering a new mechanism, researchers believe they have identified a new therapeutic target in bacteria, which could help decrease bacterial virulence and at the same time help the immune system by making bacterial recognition easier.
“It seems that bacteria shave their surface not to be recognised by the immune system” explains Sérgio Filipe who coordinated the study. “In an earlier study, also in Staphylococcus aureus, we found that bacteria have a protective layer that keeps the peptidoglycan hidden. Now we have uncovered another cover-up mechanism to remove any visible peptidoglycan above this layer”. Till now, scientists believed that the host receptors were able to recognize peptidoglycan fragments released during cell division but, instead, it’s the bacteria’s ability to trim the exposed ends of peptidoglycan molecules (which in turn releases some fragments) that makes bacteria invisible.
In this project, researchers used a peptidoglycan receptor from the fruit fly to check under what circumstances bacteria were recognized by the immune system of this insect. The receptor was able to bind to the bacteria as long as they did not produce autolysin, an enzyme typically used by bacteria during cell division, precisely to cut peptidoglycan. Removing autolysin from bacteria made recognition easier, and therefore helped infected flies to activate an effective immune response and survive the infection. Researchers concluded that bacteria produce autolysins to become invisible to the host.
Original Article
Bacterial autolysins trim cell surface peptidoglycan to prevent detection by the Drosophila innate immune system
Magda Luciana Atilano, Pedro Matos Pereira, Filipa Vaz, Maria João Catalão, Patricia Reed, Inês Ramos Grilo, Rita Gonçalves Sobral, Petros Ligoxygakis, Mariana Gomes Pinho, Sérgio Raposo Filipe
