Biology subjects

Semmler, T.

Publications and source records attributed to Semmler, T..

9 recordsLinked to original sources

bioRxiv2025

Phylodynamics and genome-wide association studies reveal the expansion of modern Streptococcus canis in Germany

Streptoccocus canis is a leading canine pathogen causing 22.4% of canine streptococcal infections. However, knowledge of factors contributing to S. canis expansion is limited. This study uses population genetics to structure a S. canis dataset of 585 isolates and identify genetic markers contributing to the success of each dominant lineage. The dataset is composed of canine, feline and bovine isolates primarily from Germany collected between the years 1996 and 2021. We performed Multi-Locus Sequence Typing (MLST) for an initial analysis and clustered the population with fastBAPS based on the whole genome. Dated phylogenies were inferred with BEAST and Genome-Wide Association Studies (GWAS) were conducted with Scoary. MLST showed that in Germany there are two dominant groups of canine S. canis, ST43 (n= 75) and ST9 (n= 51), which were grouped into BAPS-6 and BAPS-5, respectively. The BAPS-6 cluster emerged as early as 1988 with major expansion starting around 2010. We showed via GWAS that this cluster is associated with a putative Streptococcus anginosus derived integrative and conjugative element carrying a putative cysteine protease. Furthermore, the BAPS-5 cluster emerged around 1786 with a bovine/feline subcluster appearing around 1879. This subcluster is associated with a variant of the streptococcal lac operon, which appears to have resulted from an exchange with Streptococcus dysgalactiae. We present the largest population genetics study to date for S. canis where we show that its expansion is associated with genetic exchange with other streptococcal species leading to increased pathogenic potential (BAPS-6) or host adaptation (BAPS-5). ImportanceStreptococcus canis is a bacterium which poses considerable threat to the health of dogs through superficial infections. Current research could benefit from understanding the reasons for its expansion and spread into other hosts. We looked at the genomes of 585 S. canis isolates collected during a 25-year period and identified which parts of the population were the most successful. With powerful statistical methods, we found that two groups of S. canis were the most effective: a canine group which had become more pathogenic by acquiring DNA from Streptococcus anginosus, and another group which spread from dogs into cats and cows by acquiring genetic material for lactose consumption from Streptococcus dysgalactiae. For the first time, we link the expansion of major S. canis groups to genetic exchange events with closely related streptococcal species to understand S. canis evolution and spread.

microbiology↗

bioRxiv2023

Antibiotic prophylaxis and hospitalization of horses subjected to median laparotomy: gut microbiota trajectories and abundance increase of Escherichia

Horse clinics are hotspots for the accumulation and spread of clinically relevant and zoonotic multidrug-resistant bacteria, including extended-spectrum {beta}-lactamase producing (ESBL) Enterobacterales. Although median laparotomy in cases of acute equine colic is a frequently performed surgical intervention, knowledge about the effects of peri-operative antibiotic prophylaxis (PAP) based on a combination of penicillin and gentamicin on the gut microbiota is limited. Therefore, we collected fecal samples of horses from a non-hospitalized control group (CG) and from horses receiving either a pre-surgical single-shot (SSG) or a peri-operative 5-day (5DG) course of PAP. To assess differences between the two PAP regimens and the CG, all samples obtained at hospital admission (t0), on days three (t1) and ten (t2) after surgery, were screened for ESBL-producing Enterobacterales and subjected to 16S rRNA V1- V2 gene sequencing. We included 48 samples in the SSG (n=16 horses), 45 in the 5DG (n=15) and 20 in the CG (n=10). Two samples (6.5%) were positive for ESBL-producing Enterobacterales at t0 while this rate increased to 67% at t1 and decreased only slightly at t2 (61%). Shannon diversity index (SDI) was used to evaluate alpha-diversity changes, revealing that horses suffering from acute colic seemed to have a compromised fecal microbiota composition (5DG, SDImean of 5.90; SSG, SDImean of 6.17) when compared to the CG (SDImean of 6.53) at t0, although the difference lacked significance. Alpha-diversity decreased significantly in both PAP groups at t1, while at t2 the onset of microbiome recovery was noticed. Although we did not identify a significant SDImean difference with respect to PAP duration, the community structure (beta-diversity) was considerably restricted in samples of the 5DG at t1, most likely due to the ongoing administration of antibiotics. An increased abundance of Enterobacteriaceae, especially Escherichia, was noted for both study groups at t1. Further studies are needed to reveal important factors promoting the increase and residency of ESBL-producing Enterobacterales among hospitalized horses.

microbiology↗

bioRxiv2022

In-silico enrichment of bacterial plasmids by chromosomal depletion using nanopore adaptive sampling

Bacterial plasmids play a major role in the spread of antibiotic resistance genes. However, their characterization via DNA sequencing suffers from the low abundance of plasmid DNA in those samples. Although sample preparation methods can enrich the proportion of plasmid DNA before sequencing, these methods are expensive and laborious, and they might introduce a bias by enriching only for specific plasmid DNA sequences. Nanopore adaptive sampling could overcome these issues by rejecting uninteresting DNA molecules during the sequencing process. In this study, we assess the application of adaptive sampling for the enrichment of low-abundant plasmids in known bacterial isolates using two different adaptive sampling tools. We show that a significant enrichment can be achieved even on expired flow cells. By applying adaptive sampling, we also improve the quality of de novo plasmid assemblies and reduce the sequencing time. However, our experiments also highlight issues with adaptive sampling if target and non-target sequences span similar regions.

genomics↗

bioRxiv2022

Gene amplifications cause high-level resistance against albicidin in Gram-negative bacteria

Antibiotic resistance is a continuously increasing concern for public health care. Understanding resistance mechanisms and their emergence is crucial for the development of new antibiotics and their effective use. Here, we report the discovery of a gene amplification-based mechanism that imparts an up to 1000-fold increase in resistance levels against the antibiotic albicidin. We show that this mechanism protects Salmonella Typhimurium and Escherichia coli by increasing the copy number of the GyrI-like transcription regulator STM3175 (YgiV) which binds albicidin. X-ray crystallography and molecular docking studies reveal a conserved binding motif that can interact with aromatic building blocks of albicidin. Phylogenetic studies suggest that this resistance mechanism is ubiquitous in Gram-negative bacteria and our experiments confirm that STM3175 homologs can convey resistance in pathogens such as Vibrio vulnificus and Pseudomonas aeruginosa.

microbiology↗

bioRxiv2022

Genome-wide association reveals host-specific genomic traits in Escherichia coli

Escherichia coli is an opportunistic pathogen that can colonize or infect various host species. There is a significant gap in our understanding to what extent genetic lineages of E. coli are adapted or restricted to specific hosts. In addition, genomic determinants underlying such host specificity are unknown.By analyzing a randomly sampled collection of 1198 whole-genome sequenced E. coli isolates from four countries (Germany, UK, Spain, and Vietnam), obtained from five host species (human, pig, cattle, chicken, and wild boar) over 16 years, from both healthy and diseased hosts, we demonstrate that certain lineages of E. coli are frequently detected in specific hosts. We report a novel nan gene cluster, designated nan-9, putatively encoding acetylesterases and determinants of uptake and metabolism of sialic acid, to be associated with the human host as identified through genome wide association studies. In silico characterization predicts nan-9 to be involved in sialic acid (Sia) metabolism. In vitro growth experiments with a representative {Delta}nan E. coli mutant strain, using sialic acids 5-N-acetyl neuraminic acid (Neu5Ac) and N-glycolyl neuraminic acid (Neu5Gc) as the sole carbon source, indicate an impaired growth behaviour compared to the wild-type. In addition, we identified several additional E. coli genes that are potentially associated with adaptation to human, cattle and chicken hosts, but not for the pig host. Collectively, this study provides an extensive overview of genetic determinants which may mediate host specificity in E. coli. Our findings should inform risk analysis and epidemiological monitoring of (antimicrobial resistant) E. coli.

genomics↗

bioRxiv2021

Evolving a mitigation of the stress response pathway to change the basic chemistry of life

Billions of years of evolution have produced only slight variations in the standard genetic code, and the number and identity of proteinogenic amino acids have remained mostly consistent throughout all three domains of life. These observations suggest a certain rigidity of the genetic code and prompt musings as to the origin and evolution of the code. Here we conducted an adaptive laboratory evolution (ALE) to push the limits of the code restriction, by evolving Escherichia coli to fully replace tryptophan, thought to be the latest addition to the genetic code, with the analog L-{beta}-(thieno[3,2-b]pyrrolyl)alanine ([3,2]Tpa). We identified an overshooting of the stress response system to be the main inhibiting factor for limiting ancestral growth upon exposure to {beta}-(thieno[3,2-b]pyrrole ([3,2]Tp), a metabolic precursor of [3,2]Tpa, and Trp limitation. During the ALE, E. coli was able to "calm down" its stress response machinery, thereby restoring growth. In particular, the inactivation of RpoS itself, the master regulon of the general stress response, was a key event during the adaptation. Knocking out the rpoS gene in the ancestral background independent of other changes conferred growth on [3,2]Tp. Our results add additional evidence that frozen regulatory constraints rather than a rigid protein translation apparatus are Lifes gatekeepers of the canonical amino acid repertoire. This information will not only enable us to design enhanced synthetic amino acid incorporation systems but may also shed light on a general biological mechanism trapping organismal configurations in a status quo. SIGNIFICANCE STATEMENTThe (apparent) rigidity of the genetic code, as well as its universality, have long since ushered explorations into expanding the code with synthetic, new-to-nature building blocks and testing its boundaries. While nowadays even proteome-wide incorporation of synthetic amino acids has been reported on several occasions1-3, little is known about the underlying mechanisms. We here report ALE with auxotrophic E. coli that yielded successful proteome-wide replacement of Trp by its synthetic analog [3,2]Tpa accompanied with the selection for loss of RpoS4 function. Such laboratory domestication of bacteria by the acquisition of rpoS mitigation mutations is beneficial not only to overcome the stress of nutrient (Trp) starvation but also to evolve the paths to use environmental xenobiotics (e.g. [3,2]Tp) as essential nutrients for growth. We pose that regulatory constraints rather than a rigid and conserved protein translation apparatus are Lifes gatekeepers of the canonical amino acid repertoire (at least where close structural analogs are concerned). Our findings contribute a step towards understanding possible environmental causes of genetic changes and their relationship to evolution. Our evolved strain affords a platform for homogenous protein labeling with [3,2]Tpa as well as for the production of biomolecules5, which are challenging to synthesize chemically. Top-down synthetic biology will also benefit greatly from breaking through the boundaries of the frozen bacterial genetic code, as this will enable us to begin creating synthetic cells capable to utilize an expanded range of substrates essential for life.

synthetic biology↗

bioRxiv2021

Genetic diversification of persistent Mycobacterium abscessus within Cystic Fibrosis patients

Mycobacterium (M.) abscessus infections in Cystic Fibrosis (CF) patients cause a deterioration of lung function. Treatment of these multidrug-resistant pathogens is associated with severe side-effects, while frequently unsuccessful. Insight on M. abscessus genomic evolvement during chronic lung infection would be beneficial for improving treatment strategies. A longitudinal study enrolling 42 CF patients was performed at a CF center in Berlin, Germany, to elaborate phylogeny and genomic diversification of in-patient M. abscessus. Eleven of the 42 CF patients were infected with M. abscessus. Global human-transmissible M. abscessus cluster strains were isolated from five of these 11 patients. Phylogenetic analysis of 88 genomes from isolates of the 11 patients excluded occurrence of M. abscessus transmission among members of the study group. Genome sequencing and variant analysis of 30 isolates from 11 serial respiratory samples collected over four years from a chronically infected patient demonstrated accumulation of gene mutations. In total, 53 genes exhibiting non-synonymous variations were identified. Enrichment analysis emphasized genes involved in synthesis of glycopeptidolipids, genes from the embABC (arabinosyltransferase) operon, betA (glucose-methanol-choline oxidoreductase) and choD (cholesterol oxidase). Genetic diversity evolved in a variety of virulence- and resistance-associated genes. The strategy of M. abscessus populations in chronic lung infection is not clonal expansion of dominant variants, but to sustain simultaneously a wide range of genetic variants facilitating adaptation of the population to changing living conditions in the lung. Genomic diversification during chronic infection requires increased attention when new control strategies against M. abscessus infections are explored.

genomics↗

bioRxiv2021

Genome-wide insights into population structure and host specificity of Campylobacter jejuni

The zoonotic pathogen Campylobacter jejuni is among the leading causes of foodborne diseases worldwide. While C. jejuni colonises many wild animals and livestock, persistence mechanisms enabling the bacterium to adapt to host species guts are not fully understood. In order to identify putative determinants influencing host preferences of distinct lineages, bootstrapping based on stratified random sampling combined with a k-mer-based genome-wide association was conducted on 490 genomes from diverse origins in Germany and Canada. We show a strong association of both the core and the accessory genome characteristics with distinct host animal species, indicating multiple adaptive trajectories defining the evolution of C. jejuni lifestyle preferences in different ecosystems. Here, we demonstrate that adaptation towards a specific host niche ecology is most likely a long evolutionary and multifactorial process, expressed by gene absence or presence and allele variations of core genes. Several host-specific allelic variants from different phylogenetic backgrounds, including dnaE, rpoB, ftsX or pycB play important roles for genome maintenance and metabolic pathways. Thus, variants of genes important for C. jejuni to cope with specific ecological niches or hosts may be useful markers for both surveillance and future pathogen intervention strategies.

genomics↗

bioRxiv2017

Whole genome analysis reveals pathogenic potential of multi-drug resistant wastewater Escherichia coli

Wastewater treatment plants play an important role in the release of antibiotic resistance into the environment. It has been shown that wastewater contains multi-drug resistant Escherichia coli, but information on strain diversity is surprisingly scarce. Here we present an exceptionally large dataset on multidrug resistant Escherichia coli, originating from wastewater, over a thousand isolates were phenotypically characterized for twenty antibiotics and for 103 isolates whole genomes were sequenced. To our knowledge this is the first study documenting such a comprehensive diversity of multi-drug resistant Escherichia coli in wastewater. The genomic diversity of the isolates was unexpectedly high and contained a high number of resistance and virulence genes. To illustrate the genomic diversity of the isolates we calculated the pan genome of the wastewater Escherichia coli and found it to contain over sixteen thousand genes. To analyse this diverse dataset, we devised a computational approach correlating genotypic variation and resistance phenotype, this way we were able to identify not only known, but also candidate resistance genes. Finally, we could verify that the effluent of a wastewater treatment plant will contain multi-drug resistant Escherichia coli belonging to clinically important clonal groups.

bioinformatics↗