Biology subjects

Hall, R. A.

Publications and source records attributed to Hall, R. A..

10 recordsLinked to original sources

bioRxiv2026

Sequence Homology and Tissue Tropism Determine Superinfection Exclusion of Zika virus in Aedes aegypti Mediated by an insect-specific Binjari-Zika Virus Chimera

Arboviruses such as dengue, Zika, and chikungunya viruses cause widespread disease and continue to expand their geographical range due to climate change and vector spread. Insect-specific flaviviruses (ISFs) are promising biocontrol candidates of arboviruses, due to recent studies showing that prior infection with an ISF can reduce arbovirus replication in mosquitoes through superinfection exclusion (SIE). However, the route of infection, tissue tropism, pathogenesis and the mechanisms underlying SIE of ISFs in mosquitoes remain unclear. RNA interference (RNAi) is a potent antiviral response in insects, therefore it is expected that sequence homology between the ISF and the arbovirus will strengthen SIE. Here, we used ISF Binjari virus and a chimera containing the Zika virus structural proteins prME (BinJ-ZIKV) as a model system. Intrathoracic injection of BinJ-ZIKV in Aedes aegypti led to rapid systemic infection that excluded the midgut, subsequently blocking ZIKV dissemination from the midgut. SIE was strongest in tissues where primary-virus replication was highest. This spatial component of SIE was stronger when there was sequence homology between the ISF and arbovirus and displayed a strong 21nt siRNA response, suggesting RNAi contributed to the observed SIE. Upon oral inoculation, BinJ-ZIKV replicated efficiently in mosquitoes, was detected across multiple tissues, and saliva. BinJ-ZIKV also had higher infection establishment than BinJV at lower oral titres. SIE was observed for BinJ-ZIKV infection after oral exposure interfered with subsequent ZIKV midgut infection. Together, these findings support engineered ISF-chimeras as valuable experimental tools to dissect viral determinants of SIE and to optimize mosquito-based arbovirus interference strategies. ImportanceAnnually, over 400 million people are infected with mosquito-transmitted viruses. Insect-specific flaviviruses (ISFs) can interfere with the transmission of clinically important viruses through a phenomenon termed superinfection exclusion (SIE). However, the mechanisms of SIE remain poorly understood. Using a Binjari virus chimera expressing Zika virus (ZIKV) structural proteins, we show that SIE is highly tissue-specific, with exclusion of ZIKV only occurring at sites where the chimera actively replicates and induces the mosquito antiviral RNA interference pathway. We further demonstrate that incorporation of Zika virus prM and E proteins into the ISF backbone enhances infection of the mosquito midgut following oral exposure, which enables direct inhibition of ZIKV infection after a subsequent infectious blood meal. Together, these findings define a replication-dependent, tissue-specific mechanism of ISF-mediated protection and provide a framework for reducing mosquito-borne virus transmission through SIE.

microbiology↗

bioRxiv2025

Characterisation and phylogenetic analysis of Murray Valley encephalitis virus (MVEV) from the Ralph Doherty collection.

Murray Valley encephalitis virus (MVEV) is a zoonotic flavivirus endemic to Australia and Papua New Guinea. A recent outbreak of MVEV has prompted renewed concerns regarding the potential for MVEV to generate disease outbreaks. Currently, nine full length sequences of MVEV are publicly available, divided into four genotypes (G1-G4). Herein, we sequenced MVEV isolates from the Ralph Doherty Virus Collection, a virus bank with Australian field isolates dating between the 1950s-1980s, and determined their phylogenetic relationship with existing isolates to provide insights into virus evolution and genetic diversity. Additionally, we characterised isolates from different genotypes both in vitro using human neuronal cells, and in vivo using C57BL/6J mice, to provide additional insight into MVEV pathogenicity and establish models of MVEV disease that recapitulate MVEV human disease. We found 15 new full length sequences of MVEV, which primarily clustered into the dominant genotype, G1. Additionally, we show MVEV can be lethal and neuroinvasive in C57BL/6J mice, recapitulating histological lesions identified in human infection. Overall, our study contributes significant genomic sequences to the current MVEV database and establishes mouse models of disease and infection which can be used for mechanistic studies and evaluation of new interventions.

microbiology↗

bioRxiv2025

Local Adaptation of Life-History Traits in a Seasonal Environment

Populations are often spread across a spatially heterogeneous landscape, connected by migration. Consequently, the question arises whether divergent selective forces created by spatial heterogeneity can overcome the homogenising force of migration and loss of diversity through genetic drift to favour different traits across space. Such spatial heterogeneity in the population due to divergent selection is known as local adaptation. While local adaptation has been studied in a variety of settings, it remains unclear whether local adaptation of certain life-history traits can arise. Life-history traits, such as those determining an organisms fecundity (the parameter r) and ability to compete for resources (the parameter K) demonstrate unique eco-evolutionary feedback loops due to their direct relationship to individual fitness. Classic theory holds that in a constant environment, evolution maximises the populations competitive ability. Divergent selective pressures on life-history traits requires complex environmental differences, such as heterogeneous patterns of seasonality. We consider life-history evolution in a Lotka-Volterra model with three types of seasonal perturbations: repeated, sudden crashes in population size, fluctuating death rates, and fluctuating resource levels. We show that fluctuating resources cannot change the evolutionary outcome, but that sufficiently harsh population crashes or fluctuating death rates favour increased fecundity over competitive ability. Finally, we apply deterministic and stochastic modelling to study local adaptation of an island population to periodic population crashes in an island-mainland model. We find that local adaptation favouring r-selected individuals again arises when conditions are sufficiently harsh, but not so harsh that the island population cannot be sustained in the absence of migration.

evolutionary biology↗

bioRxiv2024

Vancomycin impairs macrophage fungal killing by disrupting mitochondrial morphology and function

Vancomycin is a widely prescribed antibiotic used in the treatment of Gram-positive bacterial infections. We recently showed that this antibiotic disrupted protective anti-fungal immune responses via microbiome dysbiosis, enhancing susceptibility to invasive candidiasis. Antibiotics are an independent risk factor for developing this life-threatening fungal infection, but whether microbiota-independent mechanisms also drive this association is not clear. Here, we show that vancomycin directly impairs macrophage responses to Candida albicans, the main causative agent of invasive candidiasis. Vancomycin-treated macrophages were less able to kill C. albicans despite normal phagocytosis rates and were hyper-inflammatory and more likely to die during infection. We found that vancomycin bound to macrophage mitochondria, leading to depolarisation, reduced respiratory capacity and a hyper-fragmented morphology associated with increased ROS production. Taken together, this work demonstrates direct effects of vancomycin on mammalian immune cells, helping us to understand pro-inflammatory effects of this drug and how it promotes susceptibility to life-threatening fungal infection.

immunology↗

bioRxiv2024

Gpr37 modulates the severity of inflammation-induced GI dysmotility by regulating enteric reactive gliosis.

The enteric nervous system (ENS) is contained within two layers of the gut wall and is made up of neurons, immune cells, and enteric glia cells (EGCs) that regulate gastrointestinal (GI) function. EGCs in both inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS) change in response to inflammation, referred to as reactive gliosis. Whether EGCs restricted to a specific layer or region within the GI tract alone can influence intestinal immune response is unknown. Using bulk RNA-sequencing and in situ hybridization, we identify G-protein coupled receptor Gpr37, as a gene expressed only in EGCs of the myenteric plexus, one of the two layers of the ENS. We show that Gpr37 contributes to key components of LPS-induced reactive gliosis including activation of NF-kB and IFN-y signaling and response genes, lymphocyte recruitment, and inflammation-induced GI dysmotility. Targeting Gpr37 in EGCs presents a potential avenue for modifying inflammatory processes in the ENS.

neuroscience↗

bioRxiv2024

Application of chimeric antigens to paper-based diagnostics for detection of West Nile virus infections of Crocodylus porosus: a novel animal test case

Laboratory-based diagnostics like plaque reduction neutralization tests (PRNT) and ELISA are commonly used to detect seroconversion to flavivirus infections. However, faster, qualitative screening methods are needed for quicker diagnosis and better patient outcomes. Lateral flow assays (LFAs) can provide rapid results (5-15 mins) at the point-of-care, yet few commercial flavivirus antibody detection LFAs are available. We developed an LFA using novel chimeric viral antigens produced by genetically modifying the mosquito restricted Binjari virus (BinJV) to display the outer virion proteins of pathogenic viruses such as West Nile virus (WNV). The BinJV chimeric platform offers various advantages for diagnostic assay development, including rapid construction of new chimeras in response to emerging viral variants, safe, scalable antigen manufacturing, and structural indistinguishability to the wild-type pathogenic virion. As a demonstration of feasibility, we applied chimeric WNV (BinJV/WNV) antigen to LFA as the capture/test line reagent for detection of seroconversion of crocodilians to WNV - a virus affecting crocodilians on multiple continents. We verified the antigenic conservation of the chimera when applied to the LFA detection surface using monoclonal antibodies. Using well-characterised sera (n=60) from WNV seropositive or flavivirus naive Australian saltwater crocodiles (Crocodylus porosus), we illustrated 100% sensitivity and specificity, with results achieved in less than 15 minutes. The LFA further accurately detected seroconversion in animals experimentally infected with WNV. This qualitative screening method can be performed both inside and outside of a laboratory, and the assay design will guide the optimization of similar tests for vector borne virus infection detection in both humans and other animals.

biochemistry↗

bioRxiv2022

Pseudomonas aeruginosa increases the susceptibility of Candida albicans to amphotericin B in dual species biofilms

Biofilms are the leading cause of nosocomial infections, and are hard to eradicate due to their inherent antimicrobial resistance. Candida albicans is the leading cause of nosocomial fungal infections, and is frequently co-isolated with the bacterium Pseudomonas aeruginosa from biofilms in the Cystic Fibrosis lung and severe burn wounds. The presence of C. albicans in multi-species biofilms is associated with enhanced antibacterial resistance, which is largely mediated through fungal extracellular carbohydrates sequestering the antibiotics. However, significantly less is known regarding the impact of polymicrobial biofilms on antifungal resistance. Here we show that, in dual species biofilms, P. aeruginosa enhances the sensitivity of C. albicans to amphotericin B, an effect that was biofilm specific. Transcriptional analysis combined with gene ontology enrichment analysis identified several C. albicans processes associated with oxidative stress to be differentially regulated in dual species biofilms, suggesting that P. aeruginosa exerts oxidative stress on C. albicans, likely through the actions of secreted phenazines. However, the mitochondrial superoxide dismutase SOD2 was significantly downregulated in the presence of P. aeruginosa. Monospecies biofilms of the sod2{Delta} mutant were more susceptible to amphotericin B, and the susceptibility of these biofilms was further enhanced by the addition of exogenous phenazines. Therefore, we propose that in dual species biofilms, P. aeruginosa simultaneously induces mitochondrial oxidative stress, whilst downregulating key detoxification enzymes, which prevent C. albicans mounting an appropriate oxidative stress response to amphotericin B, leading to fungal cell death. This work highlights the importance of understanding the impact of polymicrobial interactions on antimicrobial susceptibility. ImportanceBiofilms are aggregates of cells encased in an extracellular matrix, and are responsible for the majority of infections in hospitals. The Gram-negative bacterium Pseudomonas aeruginosa, and the fungal pathogen Candida albicans are frequently co-isolated from biofilms in the Cystic Fibrosis lung, and in burn wounds. Here we show that in these biofilms, P. aeruginosa secreted phenazines induce mitochondrial reactive oxygen species stress, which enhances the sensitivity of C. albicans to the antifungal amphotericin B. This work highlights the importance of understanding the impact of polymicrobial interactions on antimicrobial susceptibility.

microbiology↗

bioRxiv2021

Structural analysis of 3'UTRs in insect flaviviruses reveals novel determinant of sfRNA biogenesis and provides new insights into flavivirus evolution

Insect-specific flaviviruses (ISFs) circulate in nature due to vertical transmission in mosquitoes and do not infect vertebrates. ISFs include two distinct lineages - classical ISFs (cISFs) that evolved independently and dual host associated ISFs (dISFs) that are proposed to diverge from mosquito-borne flaviviruses (MBFs). Compared to pathogenic flaviviruses, ISFs are relatively poorly studied, and their molecular biology remains largely unexplored. In this study we focused on the characterisation of ISF 3UTRs and their ability to produce subgenomic flaviviral RNAs - noncoding viral RNAs that are known as important determinants of transmission and replication of pathogenetic flaviviruses. We demonstrated that cISFs and dISFs produce sfRNAs by employing a highly conserved mechanism of resistance to degradation by the cellular 5-3 exoribonuclease XRN1. We determined the secondary structures of complete 3UTRs and experimentally identified structured RNA elements that resist degradation by XRN1 (xrRNAs) in divergent representatives of cISF and dISF clades. We discovered a novel class of xrRNAs in dISFs and identified structurally divergent xrRNA in Anopheles-associated cISFs. Phylogenetic analyses based on sequences and secondary structures of xrRNAs and complete 3UTRs reveal that xrRNAs of cISFs and MBFs/dISFs evolved from a common xrRNA ancestor similar to the xrRNA of Anopheles-associated cISFs. Additionally, we found that duplications of xrRNAs occurred independently in ISF and MBF clades. Using ISF mutants deficient in the production of sfRNAs, we found that individual sfRNAs of ISFs have redundant functions. We conclude that duplicated xrRNAs were selected in the evolution of flaviviruses to ensure that sfRNA is produced if one of the xrRNAs lose XRN1 resistance due to mutations or misfolding.

microbiology↗

bioRxiv2020

Oestrogen promotes innate immune evasion of Candida albicans through inactivation of the alternative complement system

Gender is a risk factor for several infections that, for many pathogens, has been linked to sex hormones impacting host immunity and directly affecting microbial virulence. Candida albicans is a commensal of the urogenital tract and the predominant cause of vulvovaginal candidiasis (VVC). Factors that increase circulatory oestrogen levels like pregnancy, the use of oral contraceptives, and hormone replacement therapy predispose women to VVC, but the reasons for this are largely unknown. Here, we investigate how adaptation of C. albicans to oestrogen impacts the fungal host-pathogen interaction. Physiologically relevant concentrations of oestrogen promoted fungal virulence by enabling C. albicans to avoid the actions of the innate immune system. Oestrogen-induced innate immune evasion was mediated via inhibition of opsonophagocytosis through enhanced acquisition of the human complement regulatory protein, Factor H, on the fungal cell surface. Oestrogen induced accumulation of Factor H was dependent on the fungal cell surface protein Gpd2, with oestrogen dependent derepression of GPD2 being mediated via a non-canonical signalling pathway involving Ebp1 and Bcr1. Therefore, we propose that, in addition to affecting the antifungal potential of vaginal epithelial cells, elevated oestrogen levels predispose women to VVC by directly enhancing fungal pathogenicity through the inactivation of complement. The discovery of this new hormone sensing pathway might pave the way in explaining gender biases associated with fungal infections and may provide an alternative approach to improving womens health.

microbiology↗

bioRxiv2018

Pseudomonas aeruginosa inhibits Rhizopus microsporus germination through sequestration of free environmental iron

Rhizopus spp are the most common etiological agents of mucormycosis, causing over 90% mortality in disseminated infection. Key to pathogenesis is the ability of fungal spores to swell, germinate, and penetrate surrounding tissues. Antibiotic treatment in at-risk patients increases the probability of the patient developing mucormycosis, suggesting that bacteria have the potential to control the growth of the fungus. However, research into polymicrobial relationships involving Rhizopus spp has not been extensively explored. Here we show that co-culturing Rhizopus microsporus and Pseudomonas aeruginosa results in the inhibition of spore germination. This inhibition was mediated via the secretion of bacterial siderophores, confirming the essential role of iron for fungal growth. Addition of P. aeruginosa siderophores to R. microsporus spores in the zebrafish larval model of infection resulted in inhibition of fungal germination and reduced host mortality. Therefore, during infection antibacterial treatment may relieve bacterial imposed nutrient restriction resulting in secondary fungal infections.

microbiology↗