Biology subjects

Roberts, R. J.

Publications and source records attributed to Roberts, R. J..

13 recordsLinked to original sources

bioRxiv2026

A virion protein of an archaeal virus inhibits a Type V BREX defense system in Haloarcula hispanica

Bacteriophage Exclusion (BREX) systems are a diverse family of bacterial and archaeal defense mechanisms defined by two conserved genes encoding a putative alkaline phosphatase BrxZ (PglZ) and an ATPase BrxC (PglY). Here, we characterize a Type V BREX system from the archaeon Haloarcula hispanica. Similar to bacterial Type I BREX systems, host-virus discrimination relies on methylation of specific non-palindromic DNA motifs. Notably, the H. hispanica BREX locus encodes two methyltransferases, BrxX1 and BrxX2, which independently target distinct motifs (GTAYCCG and GACCCC). The system protects H. hispanica against three of seven tested archaeal viruses. However, two related viruses, SH1 and HHIV-2, despite encoding multiple BREX target sites, escape BREX-mediated defense. We demonstrate that a large virion protein, VP1, encoded by these viruses inhibits the BREX system, as mutant viruses carrying partial deletions of VP1 lose resistance to the host defense. Together, these findings provide the first characterization of a Type V BREX system and demonstrate that archaeal viruses can counteract BREX through virion-associated anti-defense proteins.

molecular biology↗

bioRxiv2026

Genetic engineering of Staphylococcus haemolyticus: Overcoming Restriction-Modification Barriers and Targeting Virulence Genes

Staphylococcus haemolyticus is an emerging multidrug-resistant nosocomial pathogen noted for robust biofilm formation and complex restriction-modification (RM) systems that hinder genetic manipulation. These barriers have severely limited mechanistic studies into its pathogenesis and immune evasion. Here, we report the development of a molecular toolbox that enables precise genomic engineering of clinical S. haemolyticus isolates. Using PacBio Single Molecule Real Time (SMRT) and bisulfite sequencing, we defined the complete genomes and methylomes of nine isolates, generating a functional readout of the active RM defences present in each strain. Among the RM systems identified, a Type II (PDLC03279) and a Type III (PDL3649/PDLC03643) system were significantly overrepresented in clinical isolates, suggesting a potential role in adaptation to host or hospital-associated environments. To bypass these RM barriers, we implemented a dual strategy: first, applying SyngenicDNA-based approaches to eliminate RM target motifs from genetic tools; and second, engineering a surrogate E. coli strain (JMC4) to mimic conserved S. haemolyticus methylation patterns. These tools significantly enhanced transformation efficiency and enabled targeted knockout of four putative virulence genes (sraP, secA2, capA, and capI), as well as allelic exchange of the native capsule operon with the corresponding region from a non-encapsulated isolate. To our knowledge, this is the first report of precise genomic modifications in S. haemolyticus. The establishment of robust molecular tools for transformation and genome editing lays a foundation for future functional studies of virulence and host adaptation in this resilient opportunistic pathogen. Data summaryAll genomic data were deposited in the European Nucleotide Archive and are available in NCBI under the project accession number PRJEB2705. Supporting data are provided in supplementary data files. Accession numbers are given in Table 1. O_TBL View this table: org.highwire.dtl.DTLVardef@1706c82org.highwire.dtl.DTLVardef@1e40917org.highwire.dtl.DTLVardef@10e7d3org.highwire.dtl.DTLVardef@1e3e64corg.highwire.dtl.DTLVardef@1249b03_HPS_FORMAT_FIGEXP M_TBL O_FLOATNOTable 1.C_FLOATNO O_TABLECAPTIONS. haemolyticus isolates used in this study. C_TABLECAPTION C_TBL Impact statementStaphylococcus haemolyticus is a multidrug-resistant opportunistic pathogen which causes disease in vulnerable patients. Previously, genetic modification of this pathogen was prevented due to the prevalence of strain-specific restriction modification systems, which use DNA methylation to identify and foreign DNA (including plasmids) when it enters the cells, and then destroy it using restriction enzymes. We analysed the methylomes of a selection of S. haemolyticus strains and used this data to tailor molecular tools to evade the RM systems. This enabled us to improve transformation efficiency and perform genome editing, including large-scale chromosomal modifications and targeted deletion of suspected virulence genes (a first for S. haemolyticus). Beyond its immediate relevance to researchers studying this pathogen, the tools and approaches developed here have broader utility for genetic engineering of other coagulase-negative staphylococci and bacteria with similar RM barriers. Additionally, we found that two RM systems were enriched in clinical strains, suggesting they may have a function in virulence, in addition to their roles as bacterial phage defence systems.

molecular biology↗

bioRxiv2025

Distributed control circuits across a brain-and-cord connectome

Just as genomes revolutionized molecular genetics, connectomes (maps of neurons and synapses) are transforming neuroscience. To date, the only species with complete connectomes are worms1-3 and sea squirts4 (103-104 synapses). By contrast, the fruit fly is more complex (108 synaptic connections), with a brain that supports learning and spatial memory5,6 and an intricate ventral nerve cord analogous to the vertebrate spinal cord7-11. Here we report the first densely reconstructed adult fly connectome that unites the brain and ventral nerve cord, and we leverage this resource to investigate principles of neural control. We show that effector neurons (motor neurons, endocrine cells and efferent neurons targeting the viscera) are primarily influenced by sensory neurons in the same body part, forming local feedback loops. These local loops are linked by long-range circuits involving ascending and descending neurons organized into behavior-centric modules. Single ascending and descending neurons are often positioned to influence the voluntary movements of multiple body parts, together with the endocrine cells or visceral organs that support those movements. Brain regions involved in learning and navigation supervise these circuits. These results reveal an architecture that is distributed, parallelized and embodied, reminiscent of distributed control architectures in engineered systems12,13.

neuroscience↗

bioRxiv2024

Proxi-RIMS-seq2 applied to native microbiomes uncovers hundreds of known and novel m5C methyltransferase specificities.

Methylation patterns in bacteria can be used to study Restriction-Modification (RM) or other defense systems with novel properties. While m4C and m6A methylation is well characterized mainly through PacBio sequencing, the landscape of m5C methylation is under-characterized. To bridge this gap, we performed RIMS-seq2 on microbiomes composed of resolved assemblies of distinct genomes through proximity ligation. This high-throughput approach enables the identification of m5C methylated motifs and links them to cognate methyltransferases directly on native microbiomes without the need to isolate bacterial strains. Methylation patterns can also be identified on viral DNA and compared to host DNA, strengthening evidence for virus-host interaction. Applied to three different microbiomes, the method unveils over 1900 motifs that were deposited in REBASE. The motifs include a novel 8-base recognition site (CATm5CGATG) that was experimentally validated by characterizing its cognate methyltransferase. Our findings suggest that microbiomes harbor arrays of untapped m5C methyltransferase specificities, providing insights to bacterial biology and biotechnological applications.

genomics↗

bioRxiv2024

Domainator, a flexible software suite for domain-based annotation and neighborhood analysis, identifies proteins involved in antiviral systems

The availability of large databases of biological sequences presents an opportunity for in-depth exploration of gene diversity and function. Bacterial defense systems are a rich source of diverse, but difficult to annotate genes with biotechnological applications. In this work, we present Domainator, a flexible and modular software suite for domain-based gene neighborhood and protein search, extraction, and clustering. We demonstrate the utility of Domainator through three examples related to bacterial defense systems. First, we cluster CRISPR-associated Rossman fold (CARF) containing proteins with difficult to annotate effector domains, classifying most of them as likely transcriptional regulators and a subset as likely RNAses. Second, we extract and cluster P4-like phage satellite defense hotspots and identify an abundant system related to Lamassu phage defense systems. Third, we integrate a protein language model into Domainator and use it to identify restriction enzymes with low homology to known reference sequences, validating the activity of one example in-vitro. Domainator is made available as an open-source package with detailed documentation and usage examples.

bioinformatics↗

bioRxiv2024

Genetic elements and defense systems drive diversification and evolution in Asgard archaea

Asgard Archaea are of great interest as the progenitors of Eukaryotes, but little is known about the mobile genetic elements (MGEs) that may shape their ongoing evolution. Here, we describe MGEs that replicate in Atabeyarchaeia, wetland Asgard archaea phylum represented by two complete genomes. We used soil depth-resolved population metagenomic datasets to track 18 MGEs for which genome structures were defined and precise chromosome integration sites could be identified for confident host linkage. Additionally, we identified a complete 20.67 kilobase pair (kbp) circular plasmid (the first reported for Asgard archaea) and two groups of viruses linked to Atabeyarchaeia, via CRISPR spacer targeting. Closely related 40 kbp viruses possess a hypervariable genomic region encoding combinations of specific genes for small cysteine-rich proteins structurally similar to restriction-homing endonucleases. One 10.9 kbp circularizable plasmid-like MGE integrates genomically into an Atabeyarchaeia chromosome and has a 2.5 kbp circularizable element integrated within it. The 10.9 kbp MGE encodes a highly expressed methylase with a sequence specificity matching an active methylation motif identified by PacBio sequencing. Restriction-modification of Atabeyarchaeia differs from that of another coexisting Asgard archaea Freyarchaeia which has few identified MGEs but possesses diverse defense mechanisms, including DISARM and Hachiman not found in Atabeyarchaeia. Overall, defense systems and methylation mechanisms of Asgard archaea likely modulate their interactions with MGEs, and integration/excision and copy number variation of MGEs in turn enable host genetic versatility.

microbiology↗

bioRxiv2024

Matching Excellence: ONT's Rise to Parity with PacBio in Genome Reconstruction of Non-Model Bacterium with High GC Content

Reconstruction of complete bacterial genomes is a vital aspect of microbial research, as it provides complex information about genetic content, gene ontology, and regulation. It has become a domain of 3rd generation, long-read sequencing platforms, as short-read technologies can deliver mainly fragmented genomes. PacBio platform can provide high-quality complete genomes, yet remains one of the most expensive sequencing strategies. Oxford Nanopore Technology (ONT) offers the advantage of producing the longest reads, being at the same time the most cost-effective option in terms of platform costs, as well as library preparation, and sequencing. However, ONTs error rate, although significantly reduced lately, still holds a certain level of distrust in the scientific community. In recent years, hybrid assembly of Nanopore and Illumina data has been used to solve ONTs issue with error rate and has yielded the best results in terms of genome completeness, quality, and price. However, the latest advancements in Nanopore technology, including new flow cells (R10.4.1), new library preparation chemistry (V14) and duplex-mode, updated basecallers (Dorado v0.4.1), and the realization that sequencing in dark mode results in significantly increased throughput, have had a significant impact on the quality of generated data and, thus, the recovery of complete genomes by ONT sequencing alone. In this study, we compared the data generated by ONT using three sequencing strategies (Native barcoding, RAPID barcoding, and custom-developed: BARSEQ) against PacBio and Illumina (NextSeq) as well as Illumina-ONT hybrid data. For this purpose, we employed three strains of the actinobacteria Propionibacterium freudenreichii, whose genomes have been proven difficult to reconstruct due to high GC content, regions of repeated sequences and massive genome rearrangements. Our data indicate that DNA libraries prepared with the native barcoding kit, sequenced with V14 chemistry on R10.4.1 flow cell, and assembled with Flye resulted in the reconstruction of complete genomes of overall quality highly similar to that of genomes reconstructed with PacBio. The highest level of quality can be achieved by hybrid assembly of data from the Native barcoding kit complemented with data from custom-developed BARSEQ, both sequenced on R10.4.1 flow cell. In conclusion, our results demonstrate that ONT can be used as a cost-effective sequencing strategy, without the need for complementing with other sequencing technologies, for the reconstruction of complete genomes of the highest quality.

genomics↗

bioRxiv2021

Genomic Stability and Genetic Defense Systems in Dolosigranulum pigrum a Candidate Beneficial Bacterium from the Human Microbiome

Dolosigranulum pigrum is positively associated with indicators of health in multiple epidemiological studies of human nasal microbiota. Knowledge of the basic biology of D. pigrum is a prerequisite for evaluating its potential for future therapeutic use; however, such data are very limited. To gain insight into D. pigrums chromosomal structure, pangenome and genomic stability, we compared the genomes of 28 D. pigrum strains that were collected across 20 years. Phylogenomic analysis showed closely related strains circulating over this period and closure of 19 genomes revealed highly conserved chromosomal synteny. Gene clusters involved in the mobilome and in defense against mobile genetic elements (MGEs) were enriched in the accessory genome versus the core genome. A systematic analysis for MGEs identified the first candidate D. pigrum prophage and insertion sequence. A systematic analysis for genetic elements that limit the spread of MGEs, including restriction modification (RM), CRISPR-Cas, and deity-named defense systems, revealed strain-level diversity in host defense systems that localized to specific genomic sites including one RM system hotspot. Analysis of CRISPR spacers pointed to a wealth of MGEs against which D. pigrum defends itself. These results reveal a role for horizontal gene transfer and mobile genetic elements in strain diversification while highlighting that in D. pigrum this occurs within the context of a highly stable chromosomal organization protected by a variety of defense mechanisms. IMPORTANCEDolosigranulum pigrum is a candidate beneficial bacterium with potential for future therapeutic use. This is based on its positive associations with characteristics of health in multiple studies of human nasal microbiota across the span of human life. For example, high levels of D. pigrum nasal colonization in adults predicts the absence of Staphylococcus aureus nasal colonization. Also, D. pigrum nasal colonization in young children is associated with healthy control groups in studies of middle ear infections. Our analysis of 28 genomes revealed a remarkable stability of D. pigrum strains colonizing people in the U.S. across a 20-year span. We subsequently identified factors that can influence this stability, including genomic stability, phage predators, the role of MGEs in strain-level variation and defenses against MGEs. Finally, these D. pigrum strains also lacked predicted virulence factors. Overall, these findings add additional support to the potential for D. pigrum as a therapeutic bacterium.

microbiology↗

bioRxiv2021

Rapid Identification of Methylase Specificity (RIMS-seq) jointly identifies methylated motifs and generates shotgun sequencing of bacterial genomes

DNA methylation is widespread amongst eukaryotes and prokaryotes to modulate gene expression and confer viral resistance. 5-methylcytosine (m5C) methylation has been described in genomes of a large fraction of bacterial species as part of restriction-modification systems, each composed of a methyltransferase and cognate restriction enzyme. Methylases are site-specific and target sequences vary across organisms. High-throughput methods, such as bisulfite-sequencing can identify m5C at base resolution but require specialized library preparations and Single Molecule, Real-Time (SMRT) Sequencing usually misses m5C. Here, we present a new method called RIMS-seq (Rapid Identification of Methylase Specificity) to simultaneously sequence bacterial genomes and determine m5C methylase specificities using a simple experimental protocol that closely resembles the DNA-seq protocol for Illumina. Importantly, the resulting sequencing quality is identical to DNA-seq, enabling RIMS-seq to substitute standard sequencing of bacterial genomes. Applied to bacteria and synthetic mixed communities, RIMS-seq reveals new methylase specificities, supporting routine study of m5C methylation while sequencing new genomes.

genomics↗

bioRxiv2021

Genome-Wide Identification of 5-Methylcytosine Sites in Bacterial Genomes By High-Throughput Sequencing of MspJI Restriction Fragments

Single-molecule Real-Time (SMRT) sequencing can easily identify sites of N6-methyladenine and N4-methylcytosine within DNA sequences, but similar identification of 5-methylcytosine sites is not as straightforward. In prokaryotic DNA, methylation typically occurs within specific sequence contexts, or motifs, that are a property of the methyltransferases that "write" these epigenetic marks. We present here a straightforward, cost-effective alternative to both SMRT and bisulfite sequencing for the determination of prokaryotic 5-methylcytosine methylation motifs. The method, called MFRE-Seq, relies on excision and isolation of fully methylated fragments of predictable size using MspJI-Family Restriction Enzymes (MFREs), which depend on the presence of 5-methylcytosine for cleavage. We demonstrate that MFRE-Seq is compatible with both Illumina and Ion Torrent sequencing platforms and requires only a digestion step and simple column purification of size-selected digest fragments prior to standard library preparation procedures. We applied MFRE-Seq to numerous bacterial and archaeal genomic DNA preparations and successfully confirmed known motifs and identified novel ones. This method should be a useful complement to existing methodologies for studying prokaryotic methylomes and characterizing the contributing methyltransferases.

genomics↗

bioRxiv2021

Metagenomic methylation patterns resolve complex microbial genomes

The plasticity of bacterial and archaeal genomes makes examining their ecological and evolutionary dynamics both exciting and challenging. The same mechanisms that enable rapid genomic change and adaptation confound current approaches for recovering complete genomes from metagenomes. Here, we use strain-specific patterns of DNA methylation to resolve complex bacterial genomes from the long-read metagenome of a marine microbial consortia, the "pink berries" of the Sippewissett Marsh. Unique combinations of restriction-modification (RM) systems encoded by the bacteria produced distinctive methylation profiles that accurately binned and classified metagenomic sequences. We linked the methylation patterns of each metagenome-assembled genome with encoded DNA methyltransferases and discovered new restriction modification (RM) defense systems, including novel associations of RM systems with RNase toxins. Using this approach, we finished the largest and most complex circularized bacterial genome ever recovered from a metagenome (7.9 Mb with >600 IS elements), the finished genome of Thiohalocapsa sp. PB-PSB1 the dominant bacteria in the consortia. From these methylation-binned genomes, we identified instances of lateral gene transfer between sulfur-cycling symbionts (Thiohalocapsa sp. PB-PSB1 and Desulfofustis sp. PB-SRB1), phage infection, and strain-level structural variation.

microbiology↗

bioRxiv2018

Epigenomic landscape of the human pathogen Clostridium difficile

Clostridioides difficile is a leading cause of health care-associated infections. Although significant progress has been made in the understanding of its genome, the epigenome of C. difficile and its functional impact has not been systematically explored. Here, we performed the first comprehensive DNA methylome analysis of C. difficile using 36 human isolates and observed great epigenomic diversity. We discovered an orphan DNA methyltransferase with a well-defined specificity whose corresponding gene is highly conserved across our dataset and in all ~300 global C. difficile genomes examined. Inactivation of the methyltransferase gene negatively impacted sporulation, a key step in C. difficile disease transmission, consistently supported by multi-omics data, genetic experiments, and a mouse colonization model. Further experimental and transcriptomic analysis also suggested that epigenetic regulation is associated with cell length, biofilm formation, and host colonization. These findings open up a new epigenetic dimension to characterize medically relevant biological processes in this critical pathogen. This work also provides a set of methods for comparative epigenomics and integrative analysis, which we expect to be broadly applicable to bacterial epigenomics studies.

genomics↗

bioRxiv2017

Not All Experimental Questions Are Created Equal: Accelerating Biological Data to Knowledge Transformation (BD2K) via Science Informatics, Active Learning and Artificial Intelligence

Pablo Picasso, when first told about computers, famously quipped \"Computers are useless. They can only give you answers.\" Indeed, the majority of effort in the first half-century of computational research has focused on methods for producing answers. Incredible progress has been achieved in computational modeling, simulation and optimization, across domains as diverse as astrophysics, climate studies, biomedicine, architecture, and chess. However, the use of computers to pose new questions, or prioritize existing ones, has thus far been quite limited.\n\nPicassos comment highlights the point that good questions can sometimes be more elusive than good answers. The history of science offers numerous examples of the impact of good questions. Paul Erd[o]s, the wandering monk of mathematical graph theory, offered small prizes for anyone who could prove conjectures he identified as important (1). The prizes varied in cash amounts based on the perceived complexity of the problem posed by Erd[o]s.\n\nPosing technical questions and allocating resources to answer them has taken on a new guise in the Internet age. The X-Prize foundation (http://www.xprize.org/) offers multi-million dollar bounties for grand technological goals, including goals for sequencing genomes or space exploration. Several companies provide portals where customers can place cash bounties on educational, scientific or technological challenges, while potential problem solvers can compete to produce the best solutions for these problems. Amazons Turk site (https://www.mturk.com/mturk/welcome) links people requesting performance of intellectual tasks to people willing to work on them for a fee. Such crowd-sourcing systems create markets of questions and answers, and can help allocate resources and capabilities efficiently.\n\nThis paradigm suggests a number of interesting questions for scientific research. In a resource limited environment, can funds and research capacity be allocated more efficiently? Can knowledge demand provide an alternative or complementary mechanism to traditional investigator-initiated research grants?\n\nThe fathers of Artificial Intelligence (AI) and Herbert Simon in particular envisioned the application of AI to Scientific Discovery in different forms and styles (focusing on physics). We follow on these early dreams and describe a novel approach aimed at remodeling of the biomedical research infrastructure and catalyze gene function determination. We aim to start a bold discussion of new ideas aimed towards increasing the efficiency of the allocation of research capacities, reproducibility, provenance tracking, removing redundancy and catalyzing knowledge gain with each experiment. In particular, we describe a tractable computational framework and infrastructure that can help researchers assess the potential information gain of millions of experiments before conducting them. The utility of experiments in this case is modeled as the predictive knowledge (formalized as information) to be gained as a result of performing the experiment. The experimentalist would then be empowered to select experiments that maximized information gain if they wished, recognizing that there are frequently other considerations, such as a specific technological or medical utility, that might over-ride the priority of maximizing information gain. The conceptual approach we develop is general, and here we apply it to the study of gene function.

bioinformatics↗