Biology subjects

Omsland, A.

Publications and source records attributed to Omsland, A..

6 recordsLinked to original sources

bioRxiv2026

Euo is Essential for Transcriptional Priming of Chlamydia trachomatis Elementary Bodies to Facilitate Secondary Infection.

The phylum Chlamydiota comprises obligate intracellular bacteria characterized by a highly conserved, biphasic developmental cycle. This cycle involves the transition between the infectious, metabolically quiescent elementary body (EB) and the non-infectious, replicative reticulate body (RB). While the morphological transitions of the developmental cycle are well-documented, the regulatory mechanisms governing these phenotypic shifts remain poorly understood. A primary candidate for this regulation is Euo, a conserved, phylum-specific helix-loop-helix transcription factor hypothesized to repress late-cycle genes and prevent premature differentiation. In this study, we employed CRISPR interference (CRISPRi) to knockdown euo expression in Chlamydia trachomatis to further elucidate its role in developmental regulation. Unexpectedly, euo knockdown did not significantly disrupt the primary developmental cycle; progression through RB replication, the formation of intermediate bodies (IBs), and the kinetics of late-gene expression remained largely comparable to wild-type. However, we observed a significant reduction in the production of infectious progeny. Detailed analysis revealed that while EBs were still produced and capable of entering host cells after knock down of euo, these EBs exhibited dysregulated gene expression during the germination phase of a new infection cycle. Consequently, these bacteria failed to establish a productive secondary infection. These results suggest that rather than acting as a developmental switch for differentiation during the initial infection, Euo is essential for the proper programming of EBs, ensuring transcriptional competence upon re-infection of a host cell.

microbiology↗

bioRxiv2024

The chlamydial transcriptional regulator Euo is a key switch in cell form developmental progression but is not involved in the committed step to the formation of the infectious form.

Bacteria in the genus Chlamydia are a significant health burden world wide. They infect a wide range of vertebrate animals including humans and domesticated animals. In humans, C. psittaci can cause zoonotic pneumonia while C. pneumoniae causes a variety of respiratory infections. Infections with C. trachomatis cause ocular or genital infections. All chlamydial species are obligate intracellular parasites of eukaryotic cells and are dependent on a complex infection cycle that depends on transitions between specific cell forms. This cycle consists of cell forms specialized for host cell invasion, the Elementary Body (EB), and a form specialized for intracellular replication, the Reticulate Body (RB). In addition to the EB and RB there is a transitionary cell form that mediates the transformation between the RB and the EB, the Intermediate Body (IB). In this study we ectopically expressed the regulatory protein Euo and showed that high levels of expression resulted in reversible arrest of the development cycle. The arrested chlamydial cells were trapped phenotypically at an early IB stage of the cycle. These cells had exited the cell cycle but had not shifted gene expression from RB-like to IB/EB-like. This arrested state was dependent on continued expression of Euo. When ectopic expression was reversed, Euo levels dropped in the arrested cells which led to the repression of native Euo expression and the resumption of the developmental cycle. Our data are consistent with a model where Euo expression levels impact IB maturation to the infectious EB but not the production of the IB form. ImportanceBacterial species in the Chlamydiales order infect a variety of vertebrate animals and are a global health concern. They cause various diseases in humans, including genitital and respiratory infections. The bacteria are obligate intracellular parasites that rely on a complex infectious cycle involving multiple cell forms. All species share the same life cycle, transitioning through different states to form the infectious elementary body (EB) to spread infections to new hosts. The Euo gene, encoding a DNA binding protein, is involved in regulating this cycle. This study showed that ectopic expression of Euo halted the cycle at an early stage. This arrest depended on continued Euo expression. When Euo expression was reversed, the developmental cycle resumed. Additionally, this study suggests that high levels of Euo expression affects the formation of the infectious EB, but not the production of the cell form committed to EB formation.

microbiology↗

bioRxiv2024

The T3SS structural and effector genes of Chlamydia trachomatis are expressed in distinct phenotypic cell forms.

Bacteria in the chlamydiales order are obligate intracellular parasites of eukaryotic cells. Within this order, the genus Chlamydia contains the causative agents of a number of clinically important infections of humans. Biovars of C. trachomatis are the causative agents of trachoma, the leading cause of preventable blindness worldwide, as well as sexually transmitted infections with the potential to cause pelvic inflammatory disease and infertility. Irrespective of the resulting disease, all chlamydial species share the same obligate intracellular life cycle and developmental cell forms. They are reliant on an infectious cycle consisting of at least three phenotypically distinct cell forms termed the reticulate body (RB), the intermediate body (IB) and the elementary body (EB). The EB is infectious but does not replicate. The RB replicates in the host cell but is non-infectious, while the IB is an intermediate form that transitions to the EB form. In this study, we ectopically expressed the transcriptional repressor Euo, the two nucleoid-associated proteins HctA and HctB, and the two component sensor kinase CtcB in the RB. Transcriptional analysis using RNA-seq, differential expression clustering and fluorescence in situ hybridization analysis show that the chlamydial developmental cycle is driven by three distinct regulons corresponding to the RB, IB or EB cell forms. Moreover, we show that the genes for the T3SS were cell type restricted, suggesting defined functional roles for the T3SS in specific cell forms. ImportanceChlamydia trachomatis, a sexually transmitted bacterial infection, poses a significant global health threat, causing over 100 million infections annually and leading to complications like ectopic pregnancy and infertility. This study investigates the gene expression patterns of Chlamydia trachomatis during its unique life cycle within human cells. As an obligate intracellular parasite, C. trachomatis transitions through distinct developmental stages - one for infection and dissemination, another for replication, and a third for transitioning back to the infectious form. By analyzing gene expression profiles at each stage, we identified key genes involved in these processes. Interestingly, our research also reveals the presence of two separate T3SS (Type III Secretion System) translocons expressed in distinct stages, suggesting their crucial roles in specific functions during the infection cycle.

microbiology↗

bioRxiv2022

Evaluating UV-C sensitivity of Coxiella burnetii in Skim Milk using a Bench-Scale Collimated Beam System and Comparative Study with High-Temperature Short-Time Pasteurization

Coxiella burnetii is a zoonotic Gram-negative obligate intracellular bacterial pathogen and the causative agent of Query (Q) fever in humans. Contamination of milk by C. burnetii as a consequence of livestock infection is a significant public health concern. Effective methods to inactivate C. burnetii in milk is a critical aspect of food safety. In this study, we measured optical light attenuation factors; absorption, scattering, and reflection of skim milk (SM) and considered for evaluation of delivered UV dose under stirred conditions. The accuracy of the method followed for the estimation of delivered UV dose in SM was verified by comparative studies of Escherichia coli ATCC 25922 inactivation in phosphate buffer (transparent fluid), and humic acid (opaque fluid). Absorption, scattering coefficient, and the reflectance of SM at 254 nm was measured as 19 {+/-} 0.3/cm. 26 {+/-} 0.5/cm and 10.6 %, respectively. SM inoculated with C. burnetii was irradiated using a collimated beam device equipped with a low-pressure UV-C254 nm lamp at doses from 0 - 12 mJ{middle dot}cm-2. Results showed a log-linear inactivation of C. burnetii in SM with UV-C sensitivity (D10) value of 4.1 {+/-} 0.04 mJ{middle dot}cm-2. Similar inactivation kinetics was observed with Salmonella enterica serovar Muenchen ATCC BAA 1674 in SM and thereby suggested as a suitable surrogate to C. burnetii for pilot scale UV-C processing studies of SM.

microbiology↗

bioRxiv2020

Natural Genetic Variation in Drosophila melanogaster Reveals Genes Associated with Coxiella burnetii Infection

The gram-negative bacterium Coxiella burnetii is the causative agent of Query (Q) fever in humans and coxiellosis in livestock. Association between host genetic background and Coxiella burnetii pathogenesis has been demonstrated both in humans and animals; however, specific genes associated with severity of infection remain unknown. We employed the Drosophila Genetics Reference Panel to perform a genome-wide association study and identify host genetic variants that affect Coxiella burnetii infection outcome. The analysis resulted in 64 genome-wide suggestive (P < 10-5) single nucleotide polymorphisms or gene variants in 25 unique genes. We examined the role of each gene in Coxiella burnetii infection using flies carrying a null mutation or RNAi knockdown of each gene and monitoring survival. Of the 25 candidate genes, 15 validated using at least one method. For many, this is the first report establishing involvement of these genes or their homologs with Coxiella burnetii susceptibility in any system. Among the validated genes, FER and tara play roles in the JAK-STAT, JNK, and decapentaplegic/TGF-{beta} signaling pathways that are associated with the innate immune response to Coxiella burnetii infection. Two other two validated genes, CG42673 and DIP-{varepsilon}, play roles in bacterial infection and synaptic signaling but no previous association with Coxiella burnetii pathogenesis. Furthermore, since the mammalian ortholog of CG13404 (PLGRKT) is an important regulator of macrophage function, CG13404 could play a role in Coxiella burnetii susceptibility through hemocyte regulation. These insights provide a foundation for further investigation of genetics of Coxiella burnetii susceptibility across a wide variety of hosts.

genetics↗

bioRxiv2020

Cell Type Development in Chlamydia trachomatis Follows a Program Intrinsic to the Reticulate Body.

The obligate intracellular bacterial pathogen Chlamydia trachomatis (Ctr) is reliant on an unusual developmental cycle consisting of two cell forms termed the elementary body (EB) and the reticulate body (RB). The EB is infectious and utilizes a type III secretion system and preformed effector proteins during invasion, but does not replicate. The RB replicates in the host cell but is non-infectious. This developmental cycle is central to chlamydial pathogenesis. In this study we developed mathematical models of the chlamydial developmental cycle that account for potential factors influencing the timing of RB to EB cell type switching during infection. Our models predicted that two broad categories of regulatory signals for RB to EB development could be differentiated experimentally; an "intrinsic" cell autonomous program inherent to each RB or an "extrinsic" environmental signal to which RBs respond. To experimentally differentiate between these hypotheses, we tracked the expression of Ctr developmental specific promoters using fluorescent reporters and live cell imaging. These experiments indicated that EB production was not influenced by increased MOI or by superinfection, suggesting the cycle follows an intrinsic program that is not influenced by environmental factors. Additionally, live cell imaging of these promoter constructs revealed that EB development is a multistep process linked to RB growth rate and cell division. The formation of EBs followed a cell type gene expression progression with the promoters for euo and ihtA active in RBs, while the promoter for hctA was active in early EBs/intermediate cells and finally the promoters for the true late genes, hctB, scc2, and tarp active in the maturing EB. ImportanceChlamydia trachomatis is an obligate intracellular bacteria that can cause trachoma, cervicitis, urethritis, salpingitis, and pelvic inflammatory disease. To establish infection in host cells Chlamydia must complete a multi cell type developmental cycle. The developmental cycle consists of two specialized cells; the EB which mediates infection of new cells and the RB which replicates and eventually produces more EB cells to mediate the next round of infection. By developing and testing mathematical models to discriminate between two competing hypotheses for the nature of the signal controlling RB to EB cell type switching. We demonstrate that RB to EB development follows a cell autonomous program that does not respond to environmental cues. Additionally, we show that RB to EB development is a function of cell growth and cell division. This study serves to further our understanding of the chlamydial developmental cycle that is central to the bacteriums pathogenesis.

microbiology↗