Gromadka, R. | bioRxiv Science

bioRxiv2025

Genome-Wide Identification of Essential Genes in the Invasive Streptococcus anginosus Strain

BackgroundStreptococcus anginosus, part of the Streptococcus anginosus group (SAG), is a human commensal increasingly recognized as an opportunistic pathogen responsible for abscesses formation and infections, also invasive ones. Despite its growing clinical importance, the genetic determinants of its pathogenicity remain poorly understood. ObjectivesThis study aimed to identify essential genes in S. anginosus 980/01, a bloodstream isolate, under optimal laboratory conditions using a transposon mutagenesis combined with Transposon-Directed Insertion Site Sequencing (TraDIS). MethodsA mutant library was generated using the ISS1 transposon delivered via the thermosensitive plasmid pGh9:ISS1. Following transposition, insertions were mapped using Illumina sequencing and analyzed. Essential genes were identified based on the absence of insertions and statistical filtering. ResultsThe library exhibited 98% genome saturation with over 130,000 unique insertion sites. Among 1,825 genes, 348 (19.1%) were essential, 1,446 non-essential, and 30 non-conclusive. Comparative analyses were performed with S. pyogenes MGAS5005 and S. agalactiae A909. Similarly to the latter, essential genes were enriched in functions related to translation, transcription, and cell wall biosynthesis. However, 40 genes uniquely essential to S. anginosus 980/01 were identified, suggesting unique survival strategies in S. anginosus. ConclusionsThis study presents the first genome-wide identification of essential genes for S. anginosus 980/01, highlighting conserved and unique essential genes. These findings provide a basis for understanding its pathogenic potential and for identifying novel antimicrobial targets.

microbiology↗

bioRxiv2024

Insights from comparative plastid genomics of colorless facultative pathogens Prototheca (Chlorophyta): Unveiling membrane transport and organelle division as key functions

Plastids are usually involved in photosynthesis, but the secondary loss of this function is a widespread phenomenon in various lineages of algae and plants. In addition to the loss of genes associated with photosynthesis, the plastid genomes of colorless algae are frequently reduced further. To understand the pathways of reductive evolution associated with the loss of photosynthesis, it is necessary to study a number of closely related strains. Prototheca, a chlorophytean genus of facultative pathogens, provides an excellent opportunity to study this process with its well-sampled array of diverse colorless strains. We have sequenced the plastid genomes of 13 Prototheca strains and reconstructed a comprehensive phylogeny that reveals evolutionary patterns within the genus and among its closest relatives. Our robust phylogenomic analysis revealed three independent losses of photosynthesis among the Prototheca strains and considerable coding content variability in their ptDNA. Despite this diversity, all Prototheca strains retain the same key plastid functions. These include processes related to gene expression, as well as crucial roles in fatty acid and cysteine biosynthesis, membrane transport, and organelle division. While the retention of vestigial genomes in colorless plastids is typically associated with the biosynthesis of secondary metabolites, the remarkable conservation of plastid membrane transport and organellar division systems in the nonphotosynthetic genera Prototheca and Helicosporidium provides an additional constraint against the loss of ptDNA in this lineage. Furthermore, these genes can potentially serve as targets for therapeutic intervention, indicating their importance beyond the evolutionary context.

evolutionary biology↗