Biology subjects

Gogos, A.

Publications and source records attributed to Gogos, A..

7 recordsLinked to original sources

bioRxiv2026

Discovery and characterization of a pigment produced by Streptococcus pyogenes

Streptococcus pyogenes is a major human-restricted pathogen capable of both localized and systemic diseases, as well as causing post-infectious acute and chronic rheumatological conditions. Despite its well-documented clinical importance and over a century of extensive research, gaps persist in understanding this pathogen. We report the discovery of a novel pigment produced by S. pyogenes when cultured in a replete, chemically defined medium. Color development accumulates during growth, requires exposure to oxygen, and remains associated with the bacterial cell. Though only 20% of a small strain collection produced the pigment (8 of 40), positive cultures were overrepresented by M1 and M89 serotypes. Given that pigments are critical virulence and fitness determinants in pathogens like Staphylococcus aureus and Streptococcus agalactiae, here we describe initial attempts to characterize S. pyogenes pigment biosynthesis, regulation, and potential benefits to the organism. 20,405 transposon mutants were screened for pigment loss in liquid culture, and we identified 94 independent hits enriched in pathways associated with isoprenoid biosynthesis, purine biosynthesis, guanosine transport, and mixed acid fermentation. Although color development requires oxygen, the extracted pigment did not provide antioxidative activity as compared to non-pigmented extracts. Pigment production was inhibited when the Rgg2/Rgg3 quorum-sensing system was active, though by unknown means. Treatment of RAW-Blue macrophages with the extracted pigment significantly reduced NF{kappa}B activation, suggesting a potential anti-inflammatory effect. Overall, this study describes a previously uncharacterized pigment produced by Streptococcus pyogenes and provides insights into its oxygen-dependent production and associated metabolic pathways. SIGNIFICANCEStreptococcus pyogenes is a ubiquitous pathogen responsible for [~]1.8 million severe infections and 500,000 deaths annually. This organism has not been recognized as a pigment-producing bacterium, but here we identify and characterize the production of a previously unreported colorful compound generated when cultured in a chemically defined medium. This finding reveals an underexplored aspect of S. pyogenes biology and raises the question of its contribution to pathogenesis. Given the established roles of microbial pigments in virulence and immune modulation in other pathogens, this work provides a foundation for future investigations into its functional significance and potential as a target for therapeutic or vaccine development.

microbiology↗

bioRxiv2026

3D Reconstruction of Nanoparticle Distribution in Tumor Spheroids with Volume Electron Microscopy

AO_SCPLOWBSTRACTC_SCPLOWSpatially resolved characterization of nanomaterial (NM) distribution within cellular ultrastructure is essential for understanding NM fate and activity in biological systems. Volume electron microscopy (vEM) is uniquely positioned to address this challenge, yet fully documented quantitative pipelines that simultaneously segment NMs and cellular structures remain scarce. Here, an end-to-end analytical pipeline is presented based on the example of serial block-face scanning electron microscopy (SBF-SEM) data of tumor spheroids containing nanoparticles (NPs). A hybrid segmentation strategy is adopted: a fine-tuned Cellpose-SAM model for cells and nuclei, and an empirical Bayes approach for AuNPs. The fine-tuned model outperforms both the pre-trained baseline and benchmark experiments in Amira, and shows good generalization to 2D EM datasets of varying sample types, suggesting potential as a general-purpose segmentation model for electron microscopy. Full 3D reconstruction of NP distributions reveals preferential clustering in the perinuclear region, with a median nucleus-to-NP distance of 2.57 {micro}m and NM uptake spanning several orders of magnitude across cells. Furthermore, morphological analysis of segmented cells and nuclei using 3D shape descriptors and local curvature metrics provides quantitative access to features inaccessible from single sections. Together, these results establish a reproducible, open framework for the joint quantitative analysis of NM distribution and cellular morphology in vEM data.

bioinformatics↗

bioRxiv2025

Nanoparticle Metal Mass Uptake Governs Radiosensitizing Efficacy Across 2D, 3D, and In Vivo Models

Despite extensive efforts to develop nanoparticle-based radioenhancers, clinical translation remains limited, partly due to the lack of physiologically relevant in vitro models. To address this gap, we developed a 3D spheroid model of head and neck cancer using FaDu cells and compared it directly to a corresponding in vivo model in a radiotherapy setting. The spheroids exhibited key tumor-like features, including the formation of a hypoxic core and growth kinetics comparable to in vivo tumors. Importantly, the model allowed for long-term monitoring of tumor growth and radiation response. Upon X-ray irradiation, dose-response behavior in spheroids mirrored that observed in vivo. Furthermore, TiO2, HfO2, and Au nanoparticles demonstrated consistent radiosensitization effects in both systems when matched for uptake mass. In contrast, conventional 2D clonogenic assays failed to predict in vivo performance, likely due to their lower radioresistance and unrealistic nanoparticle exposure conditions. This study introduces a robust, scalable, and clinically compatible 3D in vitro platform for preclinical screening of nanoparticle radioenhancers. The system may offer streamlining of development pipelines and support the 3R principles of reduction, replacement, and refinement in radiation oncology research.

cancer biology↗

bioRxiv2025

Understanding the kinetics of macrophage uptake and the metabolic fate of iron-carbohydrate complexes used for iron deficiency anemia treatment

Iron-carbohydrate complexes (ICCs) are widely used nanomedicines to treat iron deficiency anemia, yet their intracellular fate and the mechanisms of action underlying their differences in treatment outcomes remain poorly understood. Here, we thus performed a comprehensive dynamic characterization of two structurally distinct ICCs - iron sucrose (IS) and ferric carboxymaltose (FCM) - in primary human macrophages, key cells to the iron metabolism. By employing innovative correlative microscopy techniques, elemental analysis, and in vitro pharmacokinetic profiling, we demonstrate that the uptake, intracellular trafficking, and biodegradation of ICCs depend on their physicochemical properties. Specifically, IS is rapidly internalized and processed within endolysosomes, resulting in fast iron release and transient cytotoxicity. Conversely, FCM is sequestered in enlarged endosomes for an extended time before its biodegradation, a phenomenon we term the Hamster Effect, which leads to slower, more sustainable iron release. These results provide unprecedented insights into the metabolic fate of ICCs, enhancing our understanding of their different pharmacokinetic and pharmacodynamic profiles in vivo.

pharmacology and toxicology↗

bioRxiv2024

Cathodoluminescent and Characteristic X-ray-emissive Rare-Earth-doped Core/Shell Immunolabels for Spectromicroscopic Analysis of Cell Surface Receptors

Understanding the localization and the interactions of biomolecules at the nanoscale and in the cellular context remains challenging. Electron microscopy (EM) as a non-Abbe limited technique gives access to the cellular ultra-structure yet results in grey-scale images and averts unambiguous (co-)localization of biomolecules. Multimodal nanoparticle-based immunolabels for correlative cathodoluminescence electron microscopy (CCLEM) and energy-dispersive X-ray spectromicroscopy (EDX-SM) are presented. The single-particle STEM-cathodoluminescence (CL) and characteristic X-ray emissivity of sub-20 nm lanthanide-doped nanoparticles were exploited as unique spectral fingerprints for precise localization and label identification. To maximize the nanoparticle brightness, lanthanides were incorporated in a low-phonon host lattice and separated from the environment using a passivating shell. The core/shell nanoparticles were then functionalized with either folic (terbium-doped) or caffeic acid (europium-doped). Their potential for immunolabeling was successfully demonstrated using HeLa cells expressing different surface receptors that bind to folic or caffeic acid, respectively. Both particle populations showed single-particle CL emission along with a distinctive energy-dispersive X-ray signal, with the latter enabling colour-based localization of receptors within swift imaging times well below 2 mins per {micro}m2 while offering high resolution with a pixel size of 2.78 nm. Taken together, these results open a route to color immunolabelling based on electron spectromicroscopy. Table of Contents O_FIG O_LINKSMALLFIG WIDTH=184 HEIGHT=200 SRC="FIGDIR/small/585848v1_ufig1.gif" ALT="Figure 1"> View larger version (74K): org.highwire.dtl.DTLVardef@1f7c2d3org.highwire.dtl.DTLVardef@117be1eorg.highwire.dtl.DTLVardef@1c2bab2org.highwire.dtl.DTLVardef@16f3677_HPS_FORMAT_FIGEXP M_FIG Small (sub-20 nm) lanthanide-doped nanoparticles were successfully utilized in electron microscopy to label biological structures and contextualize them in the cells ultrastructure. Leveraging unique energy-dispersive X-ray signatures, the nanoparticles location and doping-identity was easily and fast retrieved, demonstrating the methods potential to (co)-localize labels while supplying a holistic impression of the underlying processes, as entire cells could be mapped. C_FIG

bioengineering↗

bioRxiv2021

PplD is a de-N-acetylase of the cell wall linkage unit of streptococcal rhamnopolysaccharides

The cell wall of the human bacterial pathogen Group A Streptococcus (GAS) consists of peptidoglycan decorated with the Lancefield group A carbohydrate (GAC). GAC is a promising target for the development of GAS vaccines. In this study, employing chemical, compositional, and NMR methods, we show that GAC is attached to peptidoglycan via glucosamine 1-phosphate. This structural feature makes the GAC-peptidoglycan linkage highly sensitive to cleavage by nitrous acid and resistant to mild acid conditions. Using this characteristic of the GAS cell wall, we identify PplD as a protein required for deacetylation of linkage N-acetylglucosamine (GlcNAc). X-ray structural analysis indicates that PplD performs catalysis via a modified acid/base mechanism. Genetic surveys in silico together with functional analysis indicate that PplD homologs deacetylate the polysaccharide linkage in many streptococcal species. We further demonstrate that introduction of positive charges to the cell wall by GlcNAc deacetylation protects GAS against host cationic antimicrobial proteins.

microbiology↗

bioRxiv2020

Colonization of the murine oropharynx by Streptococcus pyogenes is governed by the Rgg2/3 quorum sensing system

Streptococcus pyogenes is a human-restricted pathogen most often found in the human nasopharynx. Multiple bacterial factors are known to contribute to persistent colonization of this niche, and many are important in mucosal immunity and vaccine development. In this work, mice were infected intranasally with transcriptional regulator mutants of the Rgg2/3 quorum sensing (QS) system--a peptide-based signaling system conserved in sequenced isolates of S. pyogenes. Deletion of the QS systems transcriptional activator ({Delta}rgg2) dramatically diminished the percentage of colonized mice while deletion of the transcriptional repressor ({Delta}rgg3) increased the percentage of colonized mice compared to wild type. Stimulation of the QS system using synthetic pheromones prior to inoculation did not significantly increase the percentage of animals colonized, indicating that QS-dependent colonization is responsive to the intrinsic conditions within the host upper respiratory tract. Bacterial RNA extracted directly from oropharyngeal swabs and evaluated by quantitative RT-PCR subsequently confirmed QS upregulation within one hour of inoculation. In the nasal-associated lymphoid tissue (NALT), a muted inflammatory response to the {Delta}rgg2 bacteria suggests that their rapid elimination failed to elicit the previously characterized response to intranasal inoculation of GAS. This work identifies a new transcriptional regulatory system governing the ability of S. pyogenes to colonize the nasopharynx and provides knowledge that could help lead to decolonization therapeutics. Author SummaryStreptococcus pyogenes is responsible for a wide spectrum of diseases ranging from common pharyngitis to infrequent invasive infections like necrotizing fasciitis. The ability of this microorganism to persist in the human oropharynx predisposes colonized individuals to a variety of superficial and invasive diseases which lead to significant morbidities and mortality. Identification of the regulatory systems that augment the bacterias ability to colonize the oropharynx provides potential targets against which molecular therapeutics can be designed. Here we show that the Rgg2/3 quorum sensing system, an interbacterial communication system, governs the ability of S. pyogenes to colonize the murine oropharynx. Disruption of the systems transcriptional activator reduced colonization dramatically, eliminated the transcription of two sets of genes known to be activated by the Rgg2/3 system, and tempered the innate immune response seen when S. pyogenes is intranasally infected into the mouse.

microbiology↗