Bacteriocins of Streptococcus pneumoniae and its response to challenges by antimicrobial peptides

PhD ceremony: Ms. A Majchrzykiewicz, 16.15 uur, Academiegebouw, Broerstraat 5, Groningen

Title: Bacteriocins of Streptococcus pneumoniae and its response to challenges by antimicrobial peptides

Promotor(s): prof. O.P. Kuipers

Faculty: Mathematics and Natural Sciences

The findings of Joanna Majchrzykiewicz extend the understanding of defense mechanisms of the important human pathogen, S. pneumoniae, against antimicrobial compounds. They open up exciting possibilities to produce and engineer novel bacteriocins in vivo, which might be recognized by pharmaceutical companies as potential therapeutic alternatives to antibiotics in order to treat infectious diseases. The human pathogen Streptococcus pneumoniae is one of the bacteria that are able to produce antimicrobial substances (AMPs) called bacteriocins. Bacteriocins are small proteins that inhibit the growth or kill microorganisms in the vicinity of the producing organism. A large variability of known bacteriocins is relatively well studied among bacteria, however little is known about bacteriocins of S. pneumoniae. The thesis of Joanna Majchrzykiewicz describes nine different bacteriocin-like clusters in S. pneumoniae strains. Importantly, it shows that one of the clusters can only be produced by use of a production machinery of another, not related, bacteriocin. Furthermore, it has been suggested by Majchrzykiewicz that the function of another putative bacteriocin-like clusters is related to the general nitrogen metabolism of this bacterium. In addition she identified two novel clusters for which similar function was proposed. Notably she showed that all three clusters likely form a novel regulon in S. pneumoniae. Besides that, she investigated the transcriptional response of S. pneumoniae to three AMPs, bacitracin, nisin and LL-37. It turned out that resistance to these and other AMPs in S. pneumoniae is mediated by several putative transporters, some of which have not been associated with antimicrobial resistance in this organism before.