Biology subjects

Hunter, I. S.

Publications and source records attributed to Hunter, I. S..

7 recordsLinked to original sources

bioRxiv2026

Genome evolution during the domestication of an antibiotic-producing Streptomyces strain

The domestication of Streptomyces species for antibiotic production involves long-term, iterative mutagenesis and selection, yet the genomic changes driving enhanced production remain unclear. Analysis of five strains from an industrial lineage of Streptomyces clavuligerus using comparative genomics, transcriptomics and phenotypic profiling for dynamic genome architectures with plasmid integration events and chromosomal rearrangements, alongside the accumulation of mutations affecting metabolic pathways and global gene regulation. These changes increased precursor supply and reprogrammed transcription leading to enhanced clavulanic acid production but reduced catabolic flexibility. Complementation experiments confirmed the functional impacts of specific mutations. These findings reveal that artificial selection shapes genome evolution in industrial strains, balancing production gains with metabolic trade-offs. This work will likely inform rational design of Streptomyces strains for improved natural product production in industry while highlighting the constraints imposed by domestication on metabolic versatility. More broadly it shows that many of the evolutionary processes in industrial strain improvement programmes mirror those at play during natural selection.

microbiology↗

bioRxiv2021

Bilateral symmetry of linear streptomycete chromosomes

Here we characterise an uncommon set of telomeres from Streptomyces rimosus ATCC 10970, the parental strain of a lineage of one of the earliest-discovered antibiotic-producers. Following the closure of its genome sequence, we then compared unusual telomeres from this organism with the other five classes of replicon ends found amongst streptomycetes. Closed replicons of streptomycete chromosomes were organised with respect to their phylogeny and physical orientation, which demonstrated that different telomeres were not associated with particular clades and were likely shared amongst different strains by plasmid-driven horizontal gene transfer. Furthermore, we identified a ~50 kb origin island with conserved synteny that is located at the core of all streptomycete chromosomes and forms an axis around which symmetrical chromosome inversions can take place. Despite this chromosomal bilateral symmetry, a bias in parS sites to the right of oriC is maintained across the family Streptomycetaceae and suggests that the formation of ParB/parS nucleoprotein complexes on the right replichore is a conserved feature in streptomycetes. Consequently our studies reveal novel features of linear bacterial replicons that, through their manipulation, may lead to improvements in growth and productivity of this important industrial group of bacteria.

microbiology↗

bioRxiv2021

Novel antibiotic mode of action by repression of promoter isomerisation

Rising levels of antibiotic resistance dictate that new antibiotics with novel modes of action must be found. Here, we investigated the mode of action of a novel antibiotic that is a member of a family of synthetic DNA minor groove binding (MGB) molecules. MGB-BP-3 has successfully completed a Phase II clinical trial in humans as an orally administered drug for the treatment of chronic Clostridioides (Clostridium) difficile infections, where it outperformed the existing benchmark (vancomycin). MGB-BP-3 is active against a variety of Gram-positive pathogens including Staphylococcus aureus, which was used as the model for this study. The transcriptomic response of S. aureus to MGB-BP-3 identified downregulated promoters. DNase I and permanganate footprinting demonstrated binding to essential SigA promoters and the inhibition of promoter isomerisation by RNA polymerase holoenzyme. Promoters controlling DNA replication and peptidoglycan biosynthesis are amongst those affected by MGB-BP-3. Thus, MGB-BP-3 binds to and inhibits multiple essential promoters on the S. aureus chromosome, suggesting that evolution of resistance by drug target mutation should be unlikely. In confirmation, laboratory-directed evolution against sub-inhibitory concentrations of MGB-BP-3 resulted in no resistance whereas resistance to the single target RNA-polymerase inhibitor rifampicin arose rapidly.

molecular biology↗

bioRxiv2020

ActDES- a Curated Actinobacterial Database for Evolutionary Studies

Actinobacteria are a large and diverse phylum of bacteria that contains medically and ecologically relevant organisms. Many members are valuable sources of bioactive natural products and chemical precursors that are exploited in the clinic. These are made using the enzyme pathways encoded in their complex genomes. Whilst the number of sequenced genomes has increased rapidly in the last twenty years, the large size and complexity of many Actinobacterial genomes means that the sequences remain incomplete and consist of large numbers of contigs with poor annotation, which hinders large scale comparative genomics and evolutionary studies. To enable greater understanding and exploitation of Actinobacterial genomes, specialist genomic databases must be linked to high-quality genome sequences. Here we provide a curated database of 612 high-quality actinobacterial genomes from 80 genera, chosen to represent a broad phylogenetic group with equivalent genome reannotation. Utilising this database will provide researchers with a framework for evolutionary and metabolic studies, to enable a foundation for genome and metabolic engineering, to facilitate discovery of novel bioactive therapeutics and studies on gene family evolution. Significance as a bioresource to the communityThe Actinobacteria are a large diverse phylum of bacteria, often with large, complex genomes with a high G+C content. Sequence databases have great variation in the quality of sequences, equivalence of annotation and phylogenetic representation, which makes it challenging to undertake evolutionary and phylogenetic studies. To address this, we have assembled a curated, taxa-specific, non-redundant database to aid detailed comparative analysis of Actinobacteria. ActDES constitutes a novel resource for the community of Actinobacterial researchers that will be useful primarily for two types of analyses: (i) comparative genomic studies - facilitated by reliable identification of orthologs across a set of defined, phylogenetically-representative genomes, and (ii) phylogenomic studies which will be improved by identification of gene subsets at specified taxonomic level. These analyses can then act as a springboard for the studies of the evolution of virulence genes, the evolution of metabolism and identification of targets for metabolic engineering. Data summaryAll genome sequences used in this study can be found in the NCBI taxonomy browser https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/www.tax.cgi and are summarised along with Accession numbers in Table S1 All other data are available on Figshare https://doi.org/10.6084/m9.figshare.12167529 and https://doi.org/10.5281/zenodo.3830391 O_LIPerl script files available on GitHub https://github.com/nselem/ActDES including details of how to batch annotate genomes in RAST from the terminal https://github.com/nselem/myrast C_LIO_LISupp. Table S1 List of genomes from NCBI (Actinobacteria database.xlsx) https://doi.org/10.6084/m9.figshare.12167529 C_LIO_LICVS genome annotation files including the FASTA files of nucleotide and amino acids sequences (individual .cvs files) https://doi.org/10.6084/m9.figshare.12167880 C_LIO_LIBLAST nucleotide database (.fasta file) https://doi.org/10.6084/m9.figshare.12167724 C_LIO_LIBLAST protein database (.fasta file) https://doi.org/10.6084/m9.figshare.12167724 C_LIO_LISupp. Table S2 Expansion table genus level (Expansion table.xlsx Tab Genus level) https://doi.org/10.6084/m9.figshare.12167529 C_LIO_LISupp. Table S2 Expansion table species level (Expansion table.xlsx Tab species level) https://doi.org/10.6084/m9.figshare.12167529 C_LIO_LIAll GlcP and Glk data - blast hits from ActDES database, MUSCLE Alignment files and .nwk tree files can be found at https://doi.org/10.6084/m9.figshare.12167529 C_LIO_LIInteractive trees in Microreact for Glk tree https://microreact.org/project/w_KDfn1xA/90e6759e and associated files can be found at https://doi.org/10.6084/m9.figshare.12326441.v1 C_LIO_LIInteractive trees in Microreact for GlcP tree https://microreact.org/project/VBUdiQ5_k/0fc4622b and associated files can be found at https://doi.org/10.6084/m9.figshare.12326441.v1 C_LI

microbiology↗

bioRxiv2019

Differential transcription of expanded gene families in central carbon metabolism of Streptomyces coelicolor A3(2)

BackgroundStreptomycete bacteria are prolific producers of specialised metabolites, many of which have clinically relevant bioactivity. A striking feature of their genomes is the expansion of gene families that encode the same enzymatic function. Genes that undergo expansion events, either by horizontal gene transfer or duplication, can have a range of fates: genes can be lost, or they can undergo neo-functionalisation or sub-functionalisation. To test whether expanded gene families in Streptomyces exhibit differential expression, an RNA-Seq approach was used to examine cultures of wild-type Streptomyces coelicolor grown with either glucose or tween as the sole carbon source. ResultsRNA-Seq analysis showed that two-thirds of genes within expanded gene families show transcriptional differences when strains were grown on tween compared to glucose. In addition, expression of specialised metabolite gene clusters (actinorhodin, isorenieratane, coelichelin and a cryptic NRPS) was also influenced by carbon source. ConclusionsExpression of genes encoding the same enzymatic function had transcriptional differences when grown on different carbon sources. This transcriptional divergence enables partitioning to function under different physiological conditions. These approaches can inform metabolic engineering of industrial Streptomyces strains and may help develop cultivation conditions to activate the so-called silent biosynthetic gene clusters.

microbiology↗

bioRxiv2017

Missing pstS locus associated with an insertion in tetM in vancomycin resistant Enterococcus faecium

Multi-locus sequencing typing (MLST) is widely used to monitor the phylogeny of microbial outbreaks. However, several strains of vancomycin-resistant Enterococcus faecium (VREfm) with a missing MLST locus (pstS) have recently emerged in Australia, with a few cases also reported in England. Here, we identified similarly distinct strains circulating in two closely located hospitals in Scotland. Whole genome sequencing of five VREfm strains isolated from these hospitals identified four pstS-null strains across both hospitals, while the fifth was of a multi-locus sequence type (ST) 262, which is the first documented in the UK. All five Scottish isolates had an insertion in the tetM gene, which is associated with increased susceptibility to tetracyclines, providing no other tetracycline-resistant gene is present. Such an insertion, which encompasses a dfrG gene and two currently uncharacterised genes, was additionally identified in all tested VanA-type pstS-null VREfm strains (5 English and 18 Australian). Phylogenetic comparison with other VREfm genomes indicates that the four pstS-null Scottish isolates sequenced in this study are more closely related to pstS-null strains from Australia rather than the English pstS-null isolates. Given how rapidly such pstS-null strains have expanded in Australia, the emergence of this clone in Scotland raises concerns for a potential outbreak.

microbiology↗

bioRxiv2017

Expanding Gene Families Helps Generate The Metabolic Robustness Required For Antibiotic Biosynthesis

Introductory paragraphExpanding the genetic repertoire of an organism by gene duplication or horizontal gene transfer (HGT) can aid adaptation. Streptomyces species are prolific producers of bioactive specialised metabolites with adaptive functions in nature and some have found utility in human medicine such as antibiotics. Whilst the biosynthesis of these specialised metabolites is directed by dedicated biosynthetic gene clusters (BGCs), little attention has been focussed on how these organisms have evolved robustness into their genomes to facilitate the metabolic plasticity required to provide chemical precursors for biosynthesis. Here we show that specific expansions of gene families in central carbon metabolism have evolved and become fixed in Streptomyces bacteria to enable plasticity and robustness that maintain cell functionality whilst costly specialised metabolites are produced. These expanded gene families, in addition to being a metabolic adaptation, make excellent targets for metabolic engineering of industrial specialised metabolite producing bacteria.

microbiology↗