Biology subjects

Pitt, M. E.

Publications and source records attributed to Pitt, M. E..

9 recordsLinked to original sources

bioRxiv2026

Viruses, Proviruses and Satellites from Asgard Archaea Enrichments Reveal Complex Microbial Interactions

Asgard archaea are the closest known relatives of eukaryotes and are central to models of eukaryogenesis involving archaeal bacterial symbiosis, yet the contribution of viruses remains unexplored. Here, for the first time, we visualised unique viruses associated with Asgard archaeal cells. Additionally, we identified the first putative Asgard-archaeal virus satellite, which exhibited genomic interactions involving a bacterium, Stromatodesulfovibrio nilemahensis, providing evidence of a virus-mediated interaction between an Asgard archaeon and a bacterium. Additionally, novel proviruses of S. nilemahensis displayed distinct genomic features where predictions of alternate recombination sites suggested the acquisition of horizontally acquired genes associated with biofilm formation. Further, we comprehensively characterise (pro)viruses associated with this co-culture using high resolution cryo-electron tomography, proximity ligation (Hi-C), and metagenomics. Together, these findings expand the known diversity of Asgard archaeal viruses and establish a foundation for investigating the role of viruses in microbial symbiosis relevant to the emergence of eukaryotic life.

microbiology↗

bioRxiv2026

Interrogating the Escherichia coli epitranscriptome via CRISPR interference and Nanopore native RNA sequencing

Epitranscriptomics has recently gained significant momentum due to technological advances and translational applications, however, studies on bacterial RNA modifications remain limited. Bacterial RNA remains notoriously prone to degradation and methodologies to investigate the epitranscriptome are challenging. Prior research has shown RNA modifications modulate antimicrobial resistance, virulence and pathogenicity. This research employed CRISPR interference to knock down five known Escherichia coli rRNA modification genes (rlmF, rlmJ, rluD, rsmF and rsmG) in three E. coli strains. These isolates underwent growth curves, proteome analysis and native RNA sequencing CRISPRi adequately silenced the majority of RNA modification genes in E. coli (>80% reduction). Significant growth delays were associated with rlmF, rsmF and rsmG repression. Unique protein pathways corresponding with RNA modification loss were found for rlmJ (TreB, XylF), rluD (CysH, HycB, PutP, TrpB), rsmF (EvgA) and rsmG (OppC). Known rRNA modification sites for rluD ({Psi}) and rsmG (m7G) were detected from analysis of nanopore electrical signal, however, only a weak signal was apparent for m6A (rlmF, rlmJ) and m5C (rsmF) modifications. The inhibition of rRNA modifications resulted in mRNA modification changes including for genes ompC, cspC, dbhA, dbhB and secY. Our work provides an approach for unravelling the epitranscriptome of E. coli and gain insight into its functional role.

microbiology↗

bioRxiv2025

Profiling of Burkholderia pseudomallei variants derived from Queensland clinical isolates

Burkholderia pseudomallei (Bp), an environmental bacterium and opportunistic pathogen endemic to tropical regions, is highly adaptive and thrives in diverse environments, from soil to human hosts. Bacterial adaptation is critical for survival, virulence modulation, and persistence during infection and can manifest as colony morphotype variation (CMV). While Bp adaptation has been well studied, CMV remains poorly understood. Here, we characterized five clinical Bp isolates exhibiting heterogeneous populations with rough and smooth colony morphologies. We used phenotypic assays, whole-genome sequencing, and proteomics to investigate the molecular pathways impacted by CMV - by comparing smooth and rough morphotypes. While phenotypic differences in protease activity, haemolysis, mucoid, iron uptake and antibiotic sensitivity --including to antimicrobial agents commonly used to treat infections--were rare, these traits alone could not distinguish morphotypes or group of isolates. Genomic comparisons revealed either no differences or limited isolate-specific mutations, which does not explain the overall difference in phenotypes. In contrast, proteomic analysis uncovered consistent shifts in protein abundance related to virulence, including quorum sensing, DNA methylation, and secretion systems. Rough variants showed higher expression of EPS-associated proteins, the BpsI3/R3 quorum sensing system, and the global regulator ScmR, whereas smooth variants upregulated type III/VI secretion and siderophore biosynthesis pathways. These findings suggest that CMV is driven by phase variation and regulatory mechanisms rather than punctual genomic modifications. Our study underscores the limitations of phenotype or genome-based classification alone in the context of CMV and highlights the value of integrated multi-omics approaches to uncover CMV-associated biomarkers, with potential applications in diagnostics and the development of targeted therapies against persistent and drug-resistant Bp infections.

microbiology↗

bioRxiv2025

Customizable host and viral transcript enrichment using CRISPR-Cas9 long-read sequencing for isoform discovery and validation

Long-read RNA sequencing has been broadly utilized to examine the diversity of transcriptomes, understand differential expression and discover novel transcript isoforms. One of the major limitations of whole transcriptome sequencing is the difficulty in obtaining sufficient depth for low abundant transcripts. Methods which address this are either difficult to scale or customize: long- range PCR is customizable but difficult to scale beyond a few targets; probe hybridization panels are suited for scaling but require substantial investment to customize. In this study, we adopted RNA-guided CRISPR-Cas9 nuclease-based enrichment to target specific human and SARS-CoV-2 transcripts followed by long-read sequencing, utilizing minimal number of guide RNAs per target isoform. Our findings demonstrate that the CRISPR-Cas system is a highly effective method for customizable long-read sequencing of target transcripts while maintaining the accuracy of relative gene expression levels. The results highlight a valuable method for future research on transcript enrichment for isoform identification and low abundance transcript detection in infectious disease diagnosis.

genomics↗

bioRxiv2024

Characterisation of in vitro resistance selection against second-/last-line antibiotics in methicillin-resistant Staphylococcus aureus

SYNOPSISO_ST_ABSBackgroundC_ST_ABSThe increasing occurrence of MRSA clinical isolates harbouring reduced susceptibility to mainstay antibiotics has escalated the use of second and last line antibiotics. Hence, it is critical to evaluate the likelihood of MRSA developing clinical resistance to these antibiotics. ObjectivesOur study sought to identify the rate in which MRSA develop resistance to vancomycin, daptomycin and linezolid in vitro and further determine the mechanisms underpinning resistance. MethodsMRSA was exposed to increasing concentrations of vancomycin, daptomycin, and linezolid for 20 days, with eight replicates for each antibiotic conducted in parallel. The resulting day 20 (D20) isolates were subjected to antimicrobial susceptibility testing, whole genome sequencing, autolysis assays, and growth curves to determine bacterial fitness. ResultsExposure to vancomycin or linezolid for 20 days resulted in a subtle two-fold increase in the MIC, whereas daptomycin exposure yielded daptomycin-nonsusceptible isolates with up to 16-fold MIC increase. The MIC increase was accompanied by variable changes in relative fitness and reduced resistance to autolysis in some isolates. D20 isolates harboured mutations in genes commonly associated with resistance to the respective antibiotics (e.g. walK for vancomycin, mprF and rpoB for daptomycin, rplC for linezolid), along with several previously unreported variants. Introduction of key mutations to these identified genes in the parental strain via allelic exchange confirmed their role in the development of resistance. ConclusionsIn vitro selection against vancomycin, daptomycin, or linezolid resulted in the acquisition of mutations similar to those correlated with clinical resistance, including the associated phenotypic alterations.

microbiology↗

bioRxiv2023

MERITS: a web-based integrated MycobacterialPE/PPE protein database

MotivationPE/PPE proteins, highly abundant in the Mycobacterium genome, play a vital role in virulence and immune modulation. Understanding their functions is key to comprehending the internal mechanisms of Mycobacterium. However, a lack of dedicated resources has limited research into PE/PPE proteins. ResultsAddressing this gap, we introduce MERITS, a comprehensive 3D structure database specifically designed for PE/PPE proteins. MERITS hosts 22,353 non-redundant PE/PPE proteins, encompassing details like physicochemical properties, subcellular localisation, post-translational modification sites, protein functions, and measures of antigenicity, toxicity, and allergenicity. MERITS also includes data on their secondary and tertiary structure, along with other relevant biological information. MERITS is designed to be user-friendly, offering interactive search and data browsing Features to aid researchers in exploring the potential functions of PE/PPE proteins. MERITS is expected to become a crucial resource in the field, aiding in developing new diagnostics and vaccines by elucidating the sequence-structure-functional relationships of PE/PPE proteins. Availability and implementationMERITS is freely accessible at http://merits.unimelb-biotools.cloud.edu.au/.

bioinformatics↗

bioRxiv2023

Uncovering strain- and age- dependent differences in innate immune response to SARS-CoV-2 infection in nasal epithelia using combined short and long-read scRNA-seq

Assessing the impact of SARS-CoV-2 variants on the host is crucial with continuous emergence of new variants. We employed single-cell sequencing to investigate host transcriptomic response to ancestral and Alpha-strain SARS-CoV-2 infections within air-liquid-interface human nasal epithelial cells from adults and adolescents. Strong innate immune responses were observed across lowly-infected and bystander cell-types, and heightened in Alpha-infection. Contrastingly, the innate immune response of highly-infected cells was like mock-control cells. Alpha highly-infected cells showed increased expression of protein refolding genes compared with ancestral-strain-infected adolescent cells. Oxidative phosphorylation- and translation-related genes were down-regulated in bystander cells versus infected and mock-control cells, suggesting that the down-regulation is protective and up-regulation supports viral activity. Infected adult cells revealed up-regulation of these pathways compared with infected adolescents, implying enhanced pro-viral states in infected adults. Overall, this highlights the complexity of cell-type-, age- and viral-strain-dependent host epithelial responses to SARS-CoV-2 and the value of air-liquid-interface cultures.

immunology↗

bioRxiv2021

Long-read RNA sequencing identifies polyadenylation elongation and differential transcript usage of host transcripts during SARS-CoV-2 in vitro infection

Better methods to interrogate host-pathogen interactions during Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infections are imperative to help understand and prevent this disease. Here we implemented RNA-sequencing (RNA-seq) combined with the Oxford Nanopore Technologies (ONT) long-reads to measure differential host gene expression, transcript polyadenylation and isoform usage within various epithelial cell lines permissive and non-permissive for SARS-CoV-2 infection. SARS-CoV-2-infected and mock-infected Vero (African green monkey kidney epithelial cells), Calu-3 (human lung adenocarcinoma epithelial cells), Caco-2 (human colorectal adenocarcinoma epithelial cells) and A549 (human lung carcinoma epithelial cells) were analysed over time (0, 2, 24, 48 hours). Differential polyadenylation was found to occur in both infected Calu-3 and Vero cells during a late time point (48 hpi), with Gene Ontology (GO) terms such as viral transcription and translation shown to be significantly enriched in Calu-3 data. Poly(A) tails showed increased lengths in the majority of the differentially polyadenylated transcripts in Calu-3 and Vero cell lines (up to ~136 nt in mean poly(A) length, padj = 0.029). Of these genes, ribosomal protein genes such as RPS4X and RPS6 also showed downregulation in expression levels, suggesting the importance of ribosomal protein genes during infection. Furthermore, differential transcript usage was identified in Caco-2, Calu-3 and Vero cells, including transcripts of genes such as GSDMB and KPNA2, which have previously been implicated in SARS-CoV-2 infections. Overall, these results highlight the potential role of differential polyadenylation and transcript usage in host immune response or viral manipulation of host mechanisms during infection, and therefore, showcase the value of long-read sequencing in identifying less-explored host responses to disease.

immunology↗

bioRxiv2020

Transcriptional and epi-transcriptional dynamics of SARS-CoV-2 during cellular infection

SARS-CoV-2 uses subgenomic (sg)RNA to produce viral proteins for replication and immune evasion. We applied long-read RNA and cDNA sequencing to in vitro human and primate infection models to study transcriptional dynamics. Transcription-regulating sequence (TRS)-dependent sgRNA was upregulated earlier in infection than TRS-independent sgRNA. An abundant class of TRS-independent sgRNA consisting of a portion of ORF1ab containing nsp1 joined to ORF10 and 3UTR was upregulated at 48 hours post infection in human cell lines. We identified double-junction sgRNA containing both TRS-dependent and independent junctions. We found multiple sites at which the SARS-CoV-2 genome is consistently more modified than sgRNA, and that sgRNA modifications are stable across transcript clusters, host cells and time since infection. Our work highlights the dynamic nature of the SARS-CoV-2 transcriptome during its replication cycle. Our results are available via an interactive web-app at http://coinlab.mdhs.unimelb.edu.au/.

microbiology↗