Abstract:
Every surface of the human body is colonised by bacteria, viruses, fungi, and other members of the microbiome. The diversity and fluctuation of the microbiome in distinct niches like the gut, or the nares plays a crucial role in health and disease of every individual. During colonisation, bacteria have to overcome eliminating factors like the human innate immune system as well as the pre-existing microbiome. Hence, many bacteria have evolved various strategies to overcome this limitation. For instance, the production and uptake of secondary metabolites, which are not necessary for normal growth and division of bacterial cells. Amongst them are for example molecules with a high-affinity for distinct transition metals, like siderophores for iron uptake, or the production of antimicrobial compounds to inhibit competing cells in close vicinity to the producer. Recent studies have shown that in various staphylococci, such secondary metabolites are not only used for competition between different species but are also shared, not only as molecules but also on a DNA level as biosynthetic gene clusters. However, the regulation of many biosynthetic gene clusters of such, often metabolically costly, secondary metabolites remain often unknown. Here, we describe the regulation of the lugdunin biosynthetic gene cluster of Staphylococcus lugdunensis as well as the expression of transporters for self-immunity. We furthermore elucidate the product of another undescribed biosynthetic gene cluster of S. lugdunensis and show that the previously described ulbactin F is synthesized. Thirdly, we report that micrococcin P1 can be shared in communities at a high metabolic cost impairing bacterial fitness and found, that the reduced fitness can be omitted by adaptive mutations of the receiving strain.
We demonstrate, that the production of lugdunin and the expression of the transporters LugEF and LugGH are dependent on a positive feedback regulation. Both regulators, LugR and LugJ, interact with distinct promoter sequences and hence repress transcription initiation. Bioinformatic analysis reveals that both regulators belong to different families, however, upon binding of lugdunin to either regulator, transcription is initiated.
Furthermore, we show that S. lugdunensis produces another previously unidentified secondary metabolite. We demonstrate that the produced compound is ulbactin F. Our study shows that in S. lugdunensis ulbactin F does not exhibit an iron-binding affinity even though its regulation is iron-dependent. Preliminary results strongly support a copper-binding affinity, identifying it as a chalkophore.
Additionally, we investigate the metabolic burden of micrococcin P1 production after horizontal transfer into the lab strain Staphylococcus aureus RN4220, leading to a growth deficiency and disturbance in metabolic activity. Fitness disadvantages however could be identified to be reversible by adaptive mutation in the citZ gene encoding for the citrate synthase, leading to an evolutionary advantage.
Our studies further elucidate the impact of bacterial secondary metabolites produced by Staphylococcus spp. on various microbe-microbe interactions.
