Biology subjects

Gazioglu, O.

Publications and source records attributed to Gazioglu, O..

6 recordsLinked to original sources

bioRxiv2026

Large scale antibiotic-phage synergy studies reveal key combinations for urinary tract infection and urosepsis treatments

The growing problem of AMR infections in healthcare has prompted the search for alternative treatments, with increasing interest in bacteriophages. However, most bacteriophage-antibiotic interactions are incompletely understood, and the benefits of combining them remains context dependent. In this study, we screened thousands of phage-antibiotic combinations to assess interaction outcomes in clinical E. coli and K. pneumoniae isolates. By integrating bacteriophages into an existing, scalable clinical MIC determination platform, we identified shifts in antibiotic MIC and susceptibility, revealing patterns of additivity and antagonism. Overall, interactions showed a species-specific profile; additive interactions predominated, particularly for E. coli. Hierarchical clustering highlighted frequent positive interactions between {beta}-lactams and Tequatroviruses. Notably, closely related phages sometimes displayed divergent phenotypes, indicating that interaction outcomes cannot be inferred solely from taxonomic relatedness or genomic similarity. Taken together, these results establish a foundation for rational, evidence-based development of phage-antibiotic therapies to restore and broaden treatment options against multidrug-resistant infections.

microbiology↗

bioRxiv2025

Coexistence of two divergent TprA/PhrA cell-cell communication systems in Streptococcus mitis coordinate bacteriocin production, competence, oxidative stress responses, and interspecies competition with S. pneumoniae

Cell-cell communication (CCC) systems are key regulators of bacterial behaviors and adaptation. The human upper respiratory tract is co-colonized by commensal and pathogenic streptococci, but how CCC systems mediate their interactions remains unclear. Here, we investigated the TprA/PhrA quorum-sensing system, composed of the transcription factor TprA and its cognate signaling peptide PhrA, across Streptococcus mitis and S. pneumoniae. Comparative genomics showed that this system is broadly distributed across both species, with most strains sharing identical phrA alleles that enable interspecies signaling. In both species, the tprA/phrA module is commonly linked to the streptococcin E (sce) locus, encoding a putative bacteriocin. We show that activation of the sce operon enhances the competitive fitness of S. mitis in biofilm and infection models. In S. mitis strain C22, two diverse copies of tprA/phrA are present and differentially regulated, coordinating expression of tprA/phrA and the downstream sce locus through both shared and independent pathways. Transcriptomic analyses revealed redundancy, additivity, and cross-regulation between the two systems, linking them to the control of bacteriocin production, competence, and oxidative stress responses. Distinct promoter architectures and TprA-binding motifs underlie the functional divergence of these paralogues, highlighting how regulatory diversification can expand quorum-sensing outputs. Together, our findings show that S. mitis has evolved a flexible and layered communication network that integrates population sensing with antimicrobial and competence responses, providing a molecular basis for its competitive interactions with S. pneumoniae during colonization of the human respiratory tract.

microbiology↗

bioRxiv2025

Network rewiring of a pneumococcal communication system promotes stress adaptation in a globally successful lineage

Cell-cell communication (CCC) systems regulate bacterial behaviors and shape social interactions within microbial communities. In Streptococcus pneumoniae, several CCC systems coordinate intra- and inter-strain signaling, yet the genetic plasticity of their components and regulons remains underexplored. Here, we investigate a divergent allelic variant of the TprA/PhrA CCC system, a regulator-pheromone pair widely conserved in S. pneumoniae. We characterize PhrA1.2, the second most prevalent PhrA pheromone, as a non-signaling variant found in the globally distributed GPSC6 lineage, with presence in isolates dating back to the 1960s. In GPSC6, PhrA1.2 co-occurs with TprA1.2, a truncated transcriptional regulator carrying premature stop codons that eliminate the predicted pheromone-binding domain. Functional assays show that PhrA1.2 is non-functional, both when paired with the truncated TprA1.2 and when paired with the canonical regulator allele TprA1.1. Unexpectedly, despite its truncation, TprA1.2 activates genes involved in oxidative stress responses, including those related to iron-sulfur cluster formation and redox homeostasis. Loss of tprA1.2 impairs growth and increases hydrogen peroxide sensitivity, while in vivo experiments reveal a fitness defect during nasopharyngeal colonization. Together, our findings show that the TprA1.2 allele represents a regulator that has lost its communication component while modifying its regulon. This variant promotes adaptation to oxidative stress and contributes to colonization, demonstrating circuit rewiring of a peptide-regulator CCC system in an epidemiologically relevant S. pneumoniae lineage.

microbiology↗

bioRxiv2025

Streptolancidin D mediates intra-species competition in Streptococcus pneumoniae through the Rgg144/SHP144 quorum-sensing system

Streptococcus pneumoniae is a major colonizer of the human nasopharynx, where inter- and intra-strain competition plays a critical role in shaping population structure and influencing vaccine outcomes. Bacteriocins are key mediators of intra-species competition, yet many of their functions and regulatory mechanisms remain poorly understood. Here, we identify and characterize streptolancidin D, a previously uncharacterized bacteriocin encoded by the sldA-T locus and demonstrate its contribution to pneumococcal competition. Using isogenic streptolancidin-producing and non-producing variants of a naturally colonizing strain, we show that sldA-T contributes to inhibition of competitor strains in in vitro biofilms and during murine co-colonization. Importantly, streptolancidin D also inhibited a subset of genetically diverse pneumococcal isolates representing multiple serotypes, whereas non-producing variants showed no activity. This indicates that its effect is broad and not restricted to isogenic interactions. Genomic analysis of over 7,500 pneumococcal genomes revealed that sldA-T is present in [~]12% of isolates, with lineage-associated distribution patterns, and is consistently encoded downstream of the Rgg144/SHP144 quorum sensing system. We further demonstrate that sldA-T is regulated by this system, with sldA-T promoter activity abolished in a SHP-deficient background and partially restored by exogenous peptide stimulation. Finally, we show that streptolancidin D acts in concert with other bacteriocin systems and competence-mediated fratricide, highlighting a multifactorial antimicrobial strategy that enhances pneumococcal competitiveness. Overall, our findings identify a quorum sensing-regulated bacteriocin that contributes to pneumococcal competition and helps shape population dynamics. IMPORTANCEBacteriocins are central to bacterial competition and niche occupation, particularly in structured environments like the human nasopharynx. While several pneumococcal bacteriocins have been characterized, the functions of many remain unknown, limiting our understanding of how these systems shape strain fitness and population dynamics. We characterize streptolancidin D, a bacteriocin that enhances intraspecies competitiveness in vitro and in vivo and contributes to inhibition of genetically diverse pneumococcal strains. We demonstrate that its expression is tightly regulated by the conserved Rgg144/SHP144 quorum sensing system and that the locus is distributed and shows synteny across multiple pneumococcal lineages. Our findings reveal that streptolancidin D operates within a broader network of bacteriocins and competence-associated mechanisms that collectively shape competitive interactions. By integrating genomic, functional, and regulatory analyses, this work expands the known repertoire of pneumococcal antimicrobial systems and provides new insights into the mechanisms underpinning competition and population structure in S. pneumoniae.

microbiology↗

bioRxiv2025

Simple Sequence Repeats Mediate Phase Variation of the Mucoid Phenotype in Hypervirulent Klebsiella pneumoniae

Hypervirulent Klebsiella pneumoniae (HVKp) express a thick mucoid capsular polysaccharide which is essential for virulence and survival in the bloodstream but inhibits epithelial adhesion and invasion. The molecular mechanisms regulating capsule expression to rapidly adapt to these distinct niches are unknown. Here, we show that high frequency mutations in a poly-G repeat in the regulator of mucoid phenotype gene, rmpA, mediates reversible ON/OFF phase variation of the mucoid phenotype. We find that these mutations generate subpopulations of bacteria with reduced capsule expression and mucoidy. In vitro and in vivo infection models reveal that phase variation to the OFF state facilitates epithelial cell infection while ON switching enhances resistance to the bactericidal activity of human serum and systemic spread to the liver and spleen in a murine infection model. Genomic analysis reveals that the phase variation mechanism is a conserved feature of all HVKp and that additional novel DNA repeats in rmpD and rmpC drive different combinations of capsule mucoidy and hyperexpression phenotypes. These findings establish a mechanistic basis for how HVKp occupy such a diverse array of niches during infection, with important implications for the design and implementation of Kp-specific vaccines and therapies.

microbiology↗

bioRxiv2019

Pneumococcal attachment to epithelial cells is enhanced by the secreted peptide VP1 via its control of hyaluronic acid processing

The Gram-positive bacterium Streptococcus pneumoniae (pneumococcus) is an important human pathogen. It can either asymptomatically colonize the nasopharynx or spread to other tissues to cause mild to severe diseases. Nasopharyngeal colonization is a prerequisite for all pneumococcal diseases. We describe a molecular pathway utilized by pneumococcus to adhere to host cells and promote colonization. We demonstrate that the secreted peptide VP1 enhances pneumococcal attachment to epithelial cells. Transcriptional studies reveal that VP1 triggers the expression of operons involved in the transport and metabolism of hyaluronic acid (HA), a glycosaminoglycan present in the host extracellular matrix. Genetic experiments in the pneumococcus reveal that HA processing locus (HAL) promotes attachment. Further, overexpression of HAL genes in the {Delta}vp1 background, reveal that the influence of VP1 on attachment is mediated via its effect on HA. In addition, VP1 also enhances degradation of the HA polymer, in a process that depends on the HAL genes. siRNA experiments to knockdown host HA synthesis support this conclusion. In these knockdown cells, attachment of wild-type pneumococci is decreased, and VP1 and HAL genes no longer contribute to the attachment. Finally, experiments in a murine model of colonization reveal that VP1 and HAL genes are significant contributors to colonization. Our working model, which combines our previous and current work, is that changes in nutrient availability that influence CodY and Rgg144 lead to changes in the levels of VP1. In turn, VP1 controls the expression of a genomic region involved in the transport and metabolism of HA, and these HAL genes promote adherence in an HA-dependent manner. VP1 is encoded by a core gene, which is highly induced in vivo and is a major contributor to host adhesion, biofilm development, colonization, and virulence. In conclusion, the VP1 peptide plays a central role in a pathway that connects nutrient availability, population-level signaling, adhesion, biofilm formation, colonization, and virulence.\n\nAUTHOR SUMMARYStreptococcus pneumoniae (the pneumococcus) is a major human pathogen. This bacterium asymptomatically colonizes the human upper respiratory tract from where it can disseminate to other tissues causing mild to severe disease. Colonization is a prerequisite for dissemination and disease, such that the molecules that control colonization are high-value candidates for therapeutic interventions. Pneumococcal colonization is a population-level response, which requires attachment to host cells and biofilm development. VP1 is a signaling peptide, highly induced in the presence of host cells and in vivo, promotes biofilm development, and serves as a potent virulence determinant. In this study, we build on the molecular mechanism of VP1 function to reveal novel bacterial and host molecules that enhance adherence and colonization. Our findings suggest that host hyaluronic acid serves as an anchor for pneumococcal cells, and that genes involved in the transport and metabolism of HA promote adherence. These genes are triggered by VP1, which in turn, is controlled by regulators that respond to nutrient status of the host. Finally, our results are strongly supported by studies in a murine model of colonization. We propose that VP1 serves as a marker for colonization and a target for drug design.

microbiology↗