Modulating streptococcal phenotypes using signal peptide analogues

Emerging advances in biosensor technologies for quorum sensing signal molecules

Quorum sensing is a physiological phenomenon of microbial cell-to-cell information exchange, which relies on the quorum sensing signal molecules (QSSMs) to communicate and coordinate collective processes. Quorum sensing enables bacteria to alter their behavior as the population density and species composition of the bacterial community change. Effective detection of QSSMs is paramount for regulating microbial community behavior. However, traditional detection methods face the shortcomings of complex operation, high costs, and lack of portability. By combining the advantage of biosensing and nanomaterials, the biosensors play a pivotal significance in QSSM detection. In this review, we first briefly describe the QSSM classification and common detection techniques. Then, we provide a comprehensive summary of research progress in biosensor-based QSSM detection according to the transduction mechanism. Finally, challenges and development trends of biosensors for QSSM detection are discussed. We believe it offers valuable insights into this burgeoning research area.

Development of urea-bridged cyclic dominant negative pneumococcus competence-stimulating peptide analogs

Cyclization is a widely used approach to exert conformational restraint on linear peptide sequences. Herein, urea bridge chemistry was deployed to achieve side chain-to-side chain peptide cyclization on the Streptococcus pneumoniae CSP1-E1A peptide scaffold. To determine the effects of ring size and bridge position on the overall peptide conformation and find the ideal area within the CSP sequence for cyclization, we performed biological evaluation as well as secondary structure analysis on all the cyclic analogs. Biological evaluation results exhibited that even minor modifications to cyclic analogs for each of the cyclization positions could significantly alter the interaction between the peptide and its target receptor, ComD. Furthermore, structural analysis using circular dichroism (CD) and Trapped Ion Mobility Spectrometry (TIMS) emphasized the significance of incorporating the bridge position as a parameter to be modified, in addition to the traditional ring position and ring size parameters. Overall, our results showcase the importance of comprehensive conformational screening in fine-tuning the secondary structure of cyclic peptide analogs. This knowledge could be very useful for future studies aimed at optimizing peptide : protein interactions.

Developing multispecies quorum-sensing modulators based on the Streptococcus mitis competence-stimulating peptide

Bacteria utilize quorum sensing (QS) to coordinate many group behaviors. As such, QS has attracted significant attention as a potential mean to attenuate bacterial infectivity without introducing selective pressure for resistance development. Streptococcus mitis, a human commensal, acts as a genetic diversity reservoir for Streptococcus pneumoniae, a prevalent human pathogen. S. mitis possesses a typical comABCDE competence regulon QS circuitry; however, the competence-stimulating peptide (CSP) responsible for QS activation and the regulatory role of the competence regulon QS circuitry in S. mitis are yet to be explored. We set out to delineate the competence regulon QS circuitry in S. mitis, including confirming the identity of the native CSP signal, evaluating the molecular mechanism that governs CSP interactions with histidine kinase receptor ComD leading to ComD activation, and defining the regulatory roles of the competence regulon QS circuitry in initiating various S. mitis phenotypes. Our analysis revealed important structure-activity relationship insights of the CSP signal and facilitated the development of novel CSP-based QS modulators. Our analysis also revealed the involvement of the competence regulon in modulating competence development and biofilm formation. Furthermore, our analysis revealed that the native S. mitis CSP signal can modulate QS response in S. pneumoniae. Capitalizing on this crosstalk, we developed a multispecies QS modulator that activates both the pneumococcus ComD receptors and the S. mitis ComD-2 receptor with high potencies. The novel scaffolds identified herein can be utilized to evaluate the effects temporal QS modulation has on S. mitis as it inhabits its natural niche.

Prodigiosin as an antibiofilm agent against multidrug-resistant Staphylococcus aureus

Staphylococcus aureus is known for forming bacterial biofilms that confer increased antimicrobial resistance. Combining antibiotics with antibiofilm agents is an alternative approach, but the antibiofilm ability of prodigiosin (PG), a potential antibiotic synergist, against antimicrobial-resistant (AMR) S. aureus remains to be understood. The antibiofilm activity of PG against 29 clinical AMR S. aureus strains was evaluated using crystal violet staining, and its synergistic effects with vancomycin (VAN) was confirmed using the checkerboard test. The viability and metabolic activity of biofilms and planktonic cells were also assessed. The results revealed that PG exhibited promising inhibitory activity against biofilm formation and synergistic activity with VAN. It effectively reduced the metabolic activity of biofilms and suppressed the production of exopolysaccharides, which might be attributed to the downregulation of biofilm-related genes such as sarA, agrA, and icaA. These findings suggest that PG could be used as a preventive coating or adjuvant against biofilms in clinical settings.

Investigating the Streptococcus sinensis competence regulon through a combination of transcriptome analysis and phenotypic evaluation

Streptococcus sinensis is a recently identified member of the Mitis group of streptococci. This species has been associated with infective endocarditis; however its mechanisms of pathogenesis and virulence are not fully understood. This study aimed to investigate the influence of the competence-stimulating peptide (CSP) and the competence regulon quorum-sensing circuitry (ComABCDE) on subsequent gene transcription and expression, as well as resultant phenotypes. In this study we confirmed the native CSP identity, ascertained when endogenous CSP was produced and completed a transcriptome-wide analysis of all genes following CSP exposure. RNA sequencing analysis revealed the upregulation of genes known to be associated with competence, biofilm formation and virulence. As such, a variety of phenotypic assays were utilized to assess the correlation between increased mRNA expression and potential phenotype response, ultimately gaining insight into the effects of CSP on both gene expression and developed phenotypes. The results indicated that the addition of exogenous CSP aided in competence development and successful transformation, yielding an average transformation efficiency comparable to that of other Mitis group streptococci. Additional studies are needed to further delineate the effects of CSP exposure on biofilm formation and virulence. Overall, this study provides novel information regarding S. sinensis and provides a substantial foundation on which this species and its role in disease pathogenesis can be further investigated.