Synthetic genetic oscillators demonstrate the functional importance of phenotypic variation in pneumococcal-host interactions

Programming CRISPRi to control the lifecycle of bacteriophage T7

Clustered Regularly Interspaced Short Palindromic Repeats interference (CRISPRi), based on catalytically dead Cas9 nuclease of Streptococcus pyogenes, is a programmable and highly flexible tool to investigate gene function and essentiality in bacteria due to its ability to block transcription elongation at nearly any desired DNA target. In this study, I assess how CRISPRi can be programmed to control the life cycle and infectivity of Escherichia coli bacteriophage T7, a highly virulent and obligatory lytic phage. This is achieved by blocking the expression of critical host-dependent promoters and genes that are required for T7 genome translocation and lifecycle progression. Specifically, I focus on the promoters within the non-coding internalisation signal region and the E. coli-recognised promoter C controlling T7 RNA polymerase (T7 RNAP) expression. Fluorescent reporter assays reveal that CRISPRi targeting of promoters in the internalisation signal is only moderately effective, whereas the downregulation of the phage's own T7 RNAP occurs very efficiently. Effects on the time to lysis were strongest when the left-most promoter on the leading end of the T7 genome or T7 RNAP was targeted. The stringency of the CRISPRi approach further improved when using multiplex sgRNAs to target multiple phage regions simultaneously, resulting in a 25% increase in the time to lysis and up to an 8-fold reduction in plaque size. Overall, this study expands dCas9-dependent CRISPRi as a flexible tool to non-invasively manipulate and probe the lifecycle and infectivity of otherwise native T7 phage.

Non-invasive Streptococcus pneumoniae infections are associated with different serotypes than invasive infections, Belgium, 2020 to 2023

BackgroundDespite widely implemented pneumococcal vaccination programmes, Streptococcus pneumoniae remains a global risk for human health. Streptococcus pneumoniae can cause invasive (IPD) or non-invasive pneumococcal disease (NIPD). Surveillance is mainly focusing on IPD, assessing the full impact of pneumococcal vaccination programmes on pneumococcal disease is challenging.AimWe aimed to prospectively investigate serotype distribution and antimicrobial resistance (AMR) of S. pneumoniae isolates from patients with NIPD and compare with data on IPD isolates and with a 2007-2008 dataset on NIPD.MethodsBetween September 2020 and April 2023, we collected isolates and patient data from patients with NIPD from 23 clinical laboratories in Belgium. Capsular typing was performed by a validated Fourier-Transform Infrared spectroscopic method, and AMR was assessed with broth microdilution, using the European Committee on Antimicrobial Susceptibility Testing (EUCAST) clinical breakpoints.ResultsWe received S. pneumoniae isolates from 1,008 patients with lower respiratory tract infections (n = 760), otitis media (n = 190) and sinusitis (n = 58). Serotype 3 was the most prevalent serotype among the NIPD isolates. Serotypes not included in the 20-valent pneumococcal conjugate vaccine (PCV20) were significantly more common among the NIPD than among the IPD isolates. Antimicrobial resistance levels were significantly higher among the NIPD isolates (n = 539; 2020-2022) compared with the IPD isolates (n = 2,344; 2021-2022). Resistance to several β-lactam antimicrobials had increased significantly compared with 15 years before.ConclusionsThe NIPD isolates were strongly associated with non-vaccine serotypes and with increased AMR levels. This underlines the importance of continued NIPD surveillance for informed policy making on vaccination programmes.

Development of an inducer-free, virulence gene promoter-controlled, and fluorescent reporter-labeled CRISPR interference system in Staphylococcus aureus

The dCas9-based Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) interference (CRISPRi) gene regulation technique requires two components: a catalytically inactive Cas9 protein (dCas9) and a single-guide RNA that targets the gene of interest. This system is commonly activated by expressing dCas9 through an inducible gene promoter, but these inducers may affect cellular physiology, and accessibility and permeability of the inducer are limited in relevant model systems. Here, we have developed an alternative approach for CRISPRi activation in the clinical isolate Staphylococcus aureus USA300 LAC, where dCas9 was expressed through endogenous virulence gene promoters (vgp); coagulase, autolysin, or fibronectin-binding protein A. Additionally, we integrated a fluorescent reporter gene into the vgp-CRISPRi system to monitor the activity of the dcas9-controlling promoter. Testing the efficacy of vgp-CRISPRi by inducing growth arrest (when targeting penicillin-binding protein 1), downregulating target gene expression, or blocking coagulase-dependent coagulation of blood plasma, we provide a proof-of-concept demonstration that the virulence gene promoter-driven CRISPRi system is functional in S. aureus.IMPORTANCEThe presented inducer-free, endogenous virulence gene promoter-induced, dCas9-based Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) interference (CRISPRi system addresses several shortcomings related to the use of inducer-dependent systems such as effects on cell physiology or limitations in permeability, and it avoids the high, putatively toxic levels of dCas9 in CRISPRi systems controlled by strong, constitutive promoters.

From resonance to chaos by modulating spatiotemporal patterns through a synthetic optogenetic oscillator

Oscillations are a recurrent phenomenon in biological systems across scales, but deciphering their fundamental principles is very challenging. Here, we tackle this challenge by redesigning the wellcharacterised synthetic oscillator known as "repressilator" in Escherichia coli and controlling it using optogenetics, creating the "optoscillator". Bacterial colonies manifest oscillations as spatial ring patterns. When we apply periodic light pulses, the optoscillator behaves as a forced oscillator and we systematically investigate the properties of the rings under various light conditions. Combining experiments with mathematical modeling, we demonstrate that this simple oscillatory circuit can generate complex dynamics that are transformed into distinct spatial patterns. We report the observation of synchronisation, resonance, subharmonic resonance and period doubling. Furthermore, we present evidence of a chaotic regime. This work highlights the intricate spatiotemporal patterns accessible by synthetic oscillators and underscores the potential of our approach in revealing fundamental principles of biological oscillations.

An efficient in vivo-inducible CRISPR interference system for group A Streptococcus genetic analysis and pathogenesis studies

While genome-wide transposon mutagenesis screens have identified numerous essential genes in the significant human pathogen Streptococcus pyogenes (group A Streptococcus or GAS), many of their functions remain elusive. This knowledge gap is attributed in part to the limited molecular toolbox for controlling GAS gene expression and the bacterium's poor genetic transformability. CRISPR interference (CRISPRi), using catalytically inactive GAS Cas9 (dCas9), is a powerful approach to specifically repress gene expression in both bacteria and eukaryotes, but ironically, it has never been harnessed for controlled gene expression in GAS. In this study, we present a highly transformable and fully virulent serotype M1T1 GAS strain and introduce a doxycycline-inducible CRISPRi system for efficient repression of bacterial gene expression. We demonstrate highly efficient, oligo-based single guide RNA cloning directly to GAS, enabling the construction of a gene knockdown strain in just 2 days, in contrast to the several weeks typically required. The system is shown to be titratable and functional both in vitro and in vivo using a murine model of GAS infection. Furthermore, we provide direct in vivo evidence that the expression of the conserved cell division gene ftsZ is essential for GAS virulence, highlighting its promise as a target for emerging FtsZ inhibitors. Finally, we introduce SpyBrowse (https://veeninglab.com/SpyBrowse), a comprehensive and user-friendly online resource for visually inspecting and exploring GAS genetic features. The tools and methodologies described in this work are poised to facilitate fundamental research in GAS, contribute to vaccine development, and aid in the discovery of antibiotic targets.

IMPORTANCE

While group A Streptococcus (GAS) remains a predominant cause of bacterial infections worldwide, there are limited genetic tools available to study its basic cell biology. Here, we bridge this gap by creating a highly transformable, fully virulent M1T1 GAS strain. In addition, we established a tight and titratable doxycycline-inducible system and developed CRISPR interference (CRISPRi) for controlled gene expression in GAS. We show that CRISPRi is functional in vivo in a mouse infection model. Additionally, we present SpyBrowse, an intuitive and accessible genome browser (https://veeninglab.com/SpyBrowse). Overall, this work overcomes significant technical challenges of working with GAS and, together with SpyBrowse, represents a valuable resource for researchers in the GAS field.

Meeting report 'Microbiology 2023: from single cell to microbiome and host', an international interacademy conference in Würzburg

On September 20-22 September 2023, the international conference 'Microbiology 2023: from single cell to microbiome and host' convened microbiologists from across the globe for a very successful symposium, showcasing cutting-edge research in the field. Invited lecturers delivered exceptional presentations covering a wide range of topics, with a major emphasis on phages and microbiomes, on the relevant bacteria within these ecosystems, and their multifaceted roles in diverse environments. Discussions also spanned the intricate analysis of fundamental bacterial processes, such as cell division, stress resistance, and interactions with phages. Organized by four renowned Academies, the German Leopoldina, the French Académie des sciences, the Royal Society UK, and the Royal Swedish Academy of Sciences, the symposium provided a dynamic platform for experts to share insights and discoveries, leaving participants inspired and eager to integrate new knowledge into their respective projects. The success of Microbiology 2023 prompted the decision to host the next quadrennial academic meeting in Sweden. This choice underscores the commitment to fostering international collaboration and advancing the frontiers of microbiological knowledge. The transition to Sweden promises to be an exciting step in the ongoing global dialogue and specific collaborations on microbiology, a field where researchers will continue to push the boundaries of knowledge, understanding, and innovation not only in health and disease but also in ecology.