Biology subjects

Youngblom, M. A.

Publications and source records attributed to Youngblom, M. A..

5 recordsLinked to original sources

bioRxiv2024

Contingencies in biofilm adaptation of Mycobacterium tuberculosis

Biofilms are structured microbial communities that offer protection from a range of environmental stressors. Studies of experimental evolution within biofilms have yielded important insights into mechanisms of biofilm formation, as well as fundamental principles governing bacterial adaptation within these structured communities. Building on research using tractable species, our lab created a model for studying biofilm adaptation in Mycobacterium tuberculosis (M. tb), a fastidious, slow growing and lethal pathogen of humans. Here, we evolved eighteen M. tb populations arising from six parental genetic backgrounds under biofilm selection to investigate diversity in mechanisms of M. tb biofilm adaptation. We found that fine-scale differences among strains at the initiation of the experiment influenced the degree of replicability in their evolution. Adaptive paths were highly parallel for some strains, whereas others evolved distinct mutations across iterations of the experiment. Our data suggest that differences in replicability arise from mutational biases and variable fitness impacts of mutations across genetic backgrounds. Comparison of our results with genomic data from M. tb populations within hosts with tuberculosis (TB) revealed that several mutations associated with biofilm selection are also among the most common to emerge during natural infection. These biofilm-associated variants are not maintained in natural M. tb populations, suggesting that biofilm selection in our model mimics selection pressures that are transiently encountered by M. tb during specific phases of infection. Overall, these results support development of biofilm directed therapies for TB and demonstrate the importance of subtle genetic variation in shaping M. tb responses to changing selection pressures. SignificanceMycobacterium tuberculosis (M. tb), the causative agent of tuberculosis (TB), a difficult-to-treat, persistent infection with high mortality. One cause of this persistence is the ability of M. tb to form biofilms, aggregated structures capable of resisting antibiotics and host defenses. Here, we used an evolutionary model to investigate mechanisms of M. tb biofilm formation. We found adaptation to biofilm growth to be affected by mutational biases and interactions among mutations. Our simple in vitro model appears to mimic aspects of natural infection, as identical mutations emerge in the laboratory under biofilm selection and within hosts with TB. These results expand our knowledge of M. tb biofilm development and inform our understanding of how this bacterium responds to novel selection pressures.

evolutionary biology↗

bioRxiv2023

Portrait of a generalist bacterium: pathoadaptation, metabolic specialization and extreme environments shape diversity of Staphylococcus saprophyticus

Staphylococcus saprophyticus is a Gram-positive, coagulase-negative staphylococcus found in diverse environments including soil and freshwater, meat, and dairy foods. S. saprophyticus is also an important cause of urinary tract infections (UTIs) in humans, and mastitis in cattle. However, the genetic determinants of virulence have not yet been identified, and it remains unclear whether there are distinct sub-populations adapted to human and animal hosts. Using a diverse sample of S. saprophyticus isolates from food, animals, environmental sources, and human infections, we characterized the population structure and diversity of global populations of S. saprophyticus. We found that divergence of the two major clades of S. saprophyticus is likely facilitated by barriers to horizontal gene transfer (HGT) and differences in metabolism. Using genome-wide association study (GWAS) tools we identified the first Type VII secretion system (T7SS) described in S. saprophyticus and its association with bovine mastitis. Finally, we found that in general, strains of S. saprophyticus from different niches are genetically similar with the exception of built environments, which function as a sink for S. saprophyticus populations. This work increases our understanding of the ecology of S. saprophyticus and of the genomics of bacterial generalists. Data summaryRaw sequencing data for newly sequenced S. saprophyticus isolates have been deposited to the NCBI SRA under the project accession PRJNA928770. A list of all genomes used in this work and their associated metadata are available in the supplementary material. Custom scripts used in the comparative genomics and GWAS analyses are available here: https://github.com/myoungblom/sapro_genomics. Impact statementIt is not known whether human and cattle diseases caused by S. saprophyticus represent spillover events from a generalist adapted to survive in a range of environments, or whether the capacity to cause disease represents a specific adaptation. Seasonal cycles of S. saprophyticus UTIs and molecular epidemiological evidence suggest that these infections may be environmentally-acquired rather than via transmission from person to person. Using comparative genomics and genome wide association study tools, we found that S. saprophyticus appears adapted to inhabit a wide range of environments (generalist), with isolates from animals, food, natural environments and human infections being closely related. Bacteria that routinely switch environments, particularly between humans and animals, are of particular concern when it comes to the spread of antibiotic resistance from farm environments into human populations. This work provides a framework for comparative genomic analyses of bacterial generalists and furthers our understanding of how bacterial populations move between humans, animals, and the environment.

microbiology↗

bioRxiv2023

Adaptation of the Mycobacterium tuberculosis transcriptome to biofilm growth

Mycobacterium tuberculosis (M. tb), the causative agent of tuberculosis (TB), is a leading global cause of death from infectious disease. Biofilms are increasingly recognized as a relevant growth form during M. tb infection and may impede treatment by enabling bacterial drug and immune tolerance. M. tb has a complicated regulatory network that has been well-characterized for many relevant disease states, including dormancy and hypoxia. However, despite its importance, our knowledge of the genes and pathways involved in biofilm formation is limited. Here we characterize the biofilm transcriptomes of fully virulent clinical isolates and find that the regulatory systems underlying biofilm growth vary widely between strains and are also distinct from regulatory programs associated with other environmental cues. We used experimental evolution to investigate changes to the transcriptome during adaptation to biofilm growth and found that the application of a uniform selection pressure resulted in loss of strain-to-strain variation in gene expression, resulting in a more uniform biofilm transcriptome. The adaptive trajectories of transcriptomes were shaped by the genetic background of the M. tb population leading to convergence on a sub-lineage specific transcriptome. We identified widespread upregulation of non-coding RNA (ncRNA) as a common feature of the biofilm transcriptome and hypothesize that ncRNA function in genome-wide modulation of gene expression, thereby facilitating rapid regulatory responses to new environments. These results reveal a new facet of the M. tb regulatory system and provide valuable insight into how M. tb adapts to new environments. ImportanceUnderstanding mechanisms of resistance and tolerance in Mycobacterium tuberculosis (M. tb) can help us develop new treatments that capitalize on M. tbs vulnerabilities. Here we used transcriptomics to study both the regulation of biofilm formation in clinical isolates as well as how those regulatory systems adapt to new environments. We find that closely related clinical populations have diverse strategies for growth under biofilm conditions, and that genetic background plays a large role in determining the trajectory of evolution. These results have implications for future treatment strategies that may be informed by our knowledge of the evolutionary constraints on strain(s) from an individual infection. This work provides new information about the mechanisms of biofilm formation in M. tb and outlines a framework for population level approaches for studying bacterial adaptation.

microbiology↗

bioRxiv2022

Comparative genomics of Streptococcus oralis identifies large scale homologous recombination and a genetic variant associated with infection

The viridans group streptococci (VGS) are a large consortium of commensal streptococci that colonize the human body. Many species within this group are opportunistic pathogens causing bacteremia and infective endocarditis (IE), yet little is known about why some strains cause invasive disease. Identification of virulence determinants is complicated by the difficulty of distinguishing between the closely related species of this group. Here, we analyzed genomic data from VGS isolated from patient blood cultures with invasive infections and from oral swabs of healthy volunteers and determined the best performing methods for species identification. Using whole-genome sequence data, we characterized the population structure of a diverse sample of Streptococcus oralis isolates and found evidence of frequent recombination. We used multiple genome-wide association study tools to identify candidate determinants of invasiveness. These tools gave consistent results, leading to the discovery of a single synonymous single nucleotide polymorphism (SNP) that was significantly associated with invasiveness. This SNP is within a previously undescribed gene that is conserved across the majority of VGS species. Using growth in the presence of human serum and a simulated infective endocarditis vegetation model, we were unable to identify a phenotype for the enriched allele in laboratory assays, suggesting a phenotype may be specific to natural infection. These data highlight the power of analyzing natural populations for gaining insight into pathogenicity, particularly for organisms with complex population structures like the VGS. ImportanceThe viridians group streptococci (VGS) are a large collection of closely related commensal streptococci, with many being opportunistic pathogens causing invasive diseases such as bacteremia and infective endocarditis. Little is known about virulence determinants in these species, and there is a distinct lack of genomic information available for the VGS. In this study, we collected VGS isolates from invasive infections and healthy volunteers and performed whole genome sequencing for a suite of downstream analyses. We focused on a diverse sample of Streptococcus oralis genomes and identified high rates of recombination in the population as well as a single genome variant highly enriched in invasive isolates. The variant lies within a previously uncharacterized gene, nrdM, which shares homology with the anaerobic ribonucleoside triphosphate reductase, nrdD, and is highly conserved among VGS. This work increases our knowledge of VGS genomics and indicates that differences in virulence potential among S. oralis isolates is, at least in part, genetically determined.

microbiology↗

bioRxiv2021

Rapid adaptation of a complex trait during experimental evolution of Mycobacterium tuberculosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis (M. tb), is a leading cause of death due to infectious disease. TB is not traditionally associated with biofilms, but M. tb biofilms are linked with drug and immune tolerance and there is increasing recognition of their contribution to the recalcitrance of TB infections. Here we used M. tb experimental evolution to investigate this complex phenotype and identify candidate loci controlling biofilm formation. We identified novel candidate loci, adding to our understanding of the genetic architecture underlying M. tb biofilm development. Under selective pressure to grow as a biofilm, regulatory mutations rapidly swept to fixation and were associated with changes in multiple traits including extracellular matrix production, cell size, and growth rate. Genetic and phenotypic paths to enhanced biofilm growth varied according to the genetic background of the parent strain, suggesting that epistatic interactions are important in M. tb adaptation to changing environments.

microbiology↗