Biology subjects

Carlyon, J. A.

Publications and source records attributed to Carlyon, J. A..

4 recordsLinked to original sources

bioRxiv2026

Transformation and allelic exchange in Orientia tsutsugamushi

Orientia tsutsugamushi is a mite-transmitted obligate intracellular bacterium that causes the potentially deadly zoonosis, scrub typhus. The absence of genetic tools for Orientia have limited studies of the microbe-host interactions that underlie scrub typhus. To address this gap, we developed a protocol for transforming and achieving allelic exchange in O. tsutsugamushi str. Ikeda. From evaluating multiple cell lines and antibiotics, we found that contact-inhibited EA.hy926 human endothelial-like cells best supported Orientia replication and that chloramphenicol was an effective selection marker. We engineered a homologous recombination cassette encoding a codon-modified version of the O. tsutsugamushi ank13 gene (OTT_RS04140) (CMank13) and its promoter alongside genes for mScarlet-I and chloramphenicol acetyltransferase under control of the O. tsutsugamushi tsa22-up and tsa56-down promoters, respectively. A PCR product encompassing the cassette and chromosomal flanking regions was transformed into O. tsutsugamushi via electroporation or CaCl2, the latter of which better preserved bacterial and host cell viability. EA.hy926 cells inoculated with transformed O. tsutsugamushi were grown in glass-bottom plates in the presence of chloramphenicol and imaged by live-cell microscopy to identify cultures containing mScarlet-I positive bacteria, which could be maintained in perpetuity. Chromosomal integration of the CMank13 cassette and loss of wild-type ank13 were verified by PCR and nanopore sequencing. This report establishes platforms for genetically manipulating O. tsutsugamushi and building additional genetic tools to investigate this globally significant pathogen. IMPORTANCEOrientia tsutsugamushi causes scrub typhus, a globally emerging rickettsiosis that can have a high mortality rate and has been a known human disease since the fourth century. Of the genera of obligate intracellular bacterial pathogens that cause human disease, Orientia is the only one for which genetic tools have not been developed. This has limited understanding of O. tsutsugamushi-host dynamics that drive the bacteriums pathobiology and hindered development of novel treatment or protection strategies against scrub typhus. Here, we successfully transformed and achieved allelic exchange in O. tsutsugamushi. Transgenic bacteria were selected via antibiotic resistance, validated by PCR and nanopore sequencing, and visualized by immunofluorescence and live-cell fluorescence imaging. Our report includes detailed descriptions of empirically determined host cell cultivation, multiplicity of infection, transformation, and selection conditions to provide a foundation on which other researchers can build. Overall, this work begins to establish a genetic toolbox for O. tsutsugamushi.

genetics↗

bioRxiv2026

Small-molecule inhibition of the Orientia tsutsugamushi deubiquitylating enzyme OtDUB impairs bacterial reproduction

Scrub typhus is a potentially fatal infectious disease caused by the obligate intracellular bacterium Orientia tsutsugamushi. While antibiotic treatment is generally effective, it requires extended treatment, and drug resistance and treatment failures have emerged. O. tsutsugamushi encodes a deubiquitylating enzyme, OtDUB, which interferes with host ubiquitin-dependent pathways. OtDUB cleaves ubiquitin from various substrates, but whether this activity can be selectively targeted by small molecules is unknown. Here we have screened a chemically diverse small-molecule library using a fluorescence-based deubiquitylation assay to identify potential inhibitors of OtDUB. Two compounds, gentisic acid and amiloride hydrochloride, inhibited OtDUB activity at low dosage, with little effect on the related Wolbachia CidB or yeast Ulp1 enzymes. Computational docking predicted the compounds engage regions near the OtDUB catalytic pocket, suggesting a competitive mode of inhibition; this was supported by enzyme kinetic analyses. Neither compound caused detectable cytotoxicity in mammalian cells. Amiloride hydrochloride treatment reduced both total cellular deubiquitylating activity and the O. tsutsugamushi bacterial load in infected cells. While the identified compounds are not optimized inhibitors, they establish that bacterial pathogen-encoded deubiquitylating enzymes can be targeted by small molecules. Overall, our results provide a framework for using selective inhibitors as tools to study DUB function in genetically intractable intracellular bacteria and as potential treatments for scrub typhus.

biochemistry↗

bioRxiv2025

Obligate intracellular Orientia tsutsugamushi impedes TP53 expression to inhibit DNA damage-induced apoptosis

Infections by intracellular pathogens often cause insult to host cell DNA, which stimulates responses that ultimately eliminate the damaged cell and hence the microbial niche. p53 is an innate immunity mediator that responds to DNA damage and intracellular infection by transcriptionally activating pathways that arrest the cell cycle, repair DNA, and elicit apoptosis. How pathogens counter p53 are incompletely understood. Here, we demonstrate that the endotheliotropic obligate intracellular bacterium Orientia tsutsugamushi blocks expression of TP53 by targeting its upstream region to nearly deplete p53 levels. Contrary to the unrestricted proliferation expected based on the transcriptome of p53-deficient infected cells, Orientia arrests the cell cycle at S phase to promote bacterial replication. It protects host endothelial cells from DNA damage even if induced by etoposide and delays genotoxic-dependent apoptosis until late in infection once a high bacterial load has been achieved. TP53 downregulation, protection against genotoxicity, and inhibition of DNA damage-dependent apoptosis are executed by the Orientia nucleomodulatory effector, Ank13. Therefore, O. tsutsugamushi inhibits TP53 expression and genotoxicity to reconfigure the intracellular environment of its host cell into one that favors bacterial replication.

microbiology↗

bioRxiv2023

Orientia tsutsugamushi Ank5 directs ubiquitination and proteasomal degradation of NLRC5 to inhibit major histocompatibility complex class I expression

How intracellular bacteria subvert the major histocompatibility complex (MHC) class I pathway is poorly understood. Here, we show that the obligate intracellular bacterium Orientia tsutsugamushi uses its effector protein, Ank5, to orchestrate proteasomal degradation of the MHC class I gene transactivator, NLRC5. Ank5 uses a tyrosine in its fourth ankyrin repeat to bind the NLRC5 N-terminus while its F-box directs host SCF complex ubiquitination of K1194 in the leucine-rich repeat region that dictates NLRC5 susceptibility to Orientia- and Ank5-mediated degradation. The ability of O. tsutsugamushi strains to degrade NLRC5 correlates with ank5 genomic carriage. Ectopically expressed Ank5 that can bind but not degrade NLRC5 protects the transactivator during Orientia infection. Thus, Ank5 is an immunoevasin that uses its bipartite architecture to rid host cells of NLRC5 and MHC class I molecules. This study offers insight into how intracellular pathogens can impair MHC class I expression to benefit their survival.

microbiology↗