Biology subjects

Westmann, C. A.

Publications and source records attributed to Westmann, C. A..

6 recordsLinked to original sources

bioRxiv2026

Regulatory scope shapes the adaptive landscapes of bacterial transcription factor binding sites

Transcription factors (TFs) span a regulatory hierarchy from local regulators that control one or few genes to global regulators that regulate hundreds. Local TFs typically operate through few, highly specific binding sites; global TFs through many of varying affinity. Whether this difference in TF biology systematically affects TFBS evolution is unclear. Here, we address this question by studying experimentally mapped adaptive landscapes of transcription factor binding sites (TFBSs) for five bacterial TFs that differ in their regulatory scope -- TetR (local), LasR (semi-global), and CRP, Fis, and IHF (global). All landscapes are rugged and epistatic, but three topographic properties vary systematically with regulatory scope. First, mean mutational robustness increases from local to global TFs. Second, high-regulation-strength peaks are clustered in the local landscape but dispersed in the global ones. Third, adaptive evolution reaches high adaptive peaks more readily in local landscapes. All five landscapes also harbor many evolvability-enhancing (EE) mutations, which increase the likelihood that subsequent mutations are beneficial. The fraction of these mutations is approximately an order of magnitude higher than previously reported for a protein landscape. Populations experiencing EE mutations consistently reach higher regulation strength, an effect that is strongest in the local TetR landscape. Together, these results identify regulatory scope as an organising axis of TFBS adaptive landscapes.

evolutionary biology↗

bioRxiv2024

Entangled adaptive landscapes facilitate the evolution of gene regulation by exaptation

Exaptation, the co-option of existing traits for new functions, is a central process in Darwinian evolution. However, the molecular changes leading to exaptations remain unclear. We investigated the potential of bacterial transcription factor binding sites (TFBSs) to evolve exaptively for the three global E. coli transcription factors (TFs) CRP, Fis, and IHF. Using a massively parallel reporter assay, we mapped three combinatorially complete adaptive landscapes, encompassing all intermediate sequences between three pairs of strong TFBSs for each TF. Our results revealed that these landscapes are smooth and navigable, with a monotonic relationship between mutations and their impact on gene regulation. Starting from a strong TFBS for one of our TFs, Darwinian evolution can create a strong TFBS for another TF through a small number of individually adaptive mutations. Notably, most intermediate genotypes are prone to transcriptional crosstalk - gene regulation mediated by both TFs. Because our landscapes are smooth, Darwinian evolution can also easily create TFBSs that show such crosstalk whenever it is adaptive. We also present evidence of exaptive evolution and crosstalk from an analysis of bacterial genomes. Our study presents the first in vivo evidence that new TFBSs can evolve exaptively through multiple small and adaptive mutational steps. It also highlights the importance of regulatory crosstalk for the diversification of gene regulation.

evolutionary biology↗

bioRxiv2024

Engineering a novel probiotic toolkit in Escherichia coli Nissle1917 for sensing and mitigating gut inflammatory diseases

Inflammatory Bowel Disease (IBD) is characterized by chronic intestinal inflammation with no cure and limited treatment options that often have systemic side effects. In this study, we developed a target-specific system to potentially treat IBD by engineering the probiotic bacterium Escherichia coli Nissle 1917 (EcN). Our modular system comprises three components: a transcription factor-based sensor (NorR) capable of detecting the inflammation biomarker nitric oxide, a type 1 hemolysin secretion system, and a therapeutic cargo consisting of a library of humanized anti-TNF nanobodies. Despite a reduction in sensitivity, our system demonstrated a concentration-dependent response to nitric oxide, successfully secreting functional nanobodies with binding affinities comparable to the commonly used drug Adalimumab, as confirmed by ELISA and in vitro assays. This newly validated nanobody library expands EcN therapeutic capabilities. The adopted secretion system, also characterized for the first time in EcN, can be further adapted as a platform for screening and purifying proteins of interest. Additionally, we provided a mathematical framework to assess critical parameters in engineering probiotic systems, including the production and diffusion of relevant molecules, bacterial colonization rates, and particle interactions. This integrated approach expands the synthetic biology toolbox for EcN-based therapies, providing novel parts, circuits, and a model for tunable responses at inflammatory hotspots. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=166 HEIGHT=200 SRC="FIGDIR/small/599326v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@173d556org.highwire.dtl.DTLVardef@1bb2ae1org.highwire.dtl.DTLVardef@fc1fcborg.highwire.dtl.DTLVardef@8b5f7f_HPS_FORMAT_FIGEXP M_FIG C_FIG Graphical Table of Contents. The engineered probiotic system: Inflamed intestinal cells release the inflammatory regulator TNF (depicted as red squares), which promotes inflammation through a positive feedback loop. Concurrently, these cells produce large amounts of nitric oxide (NO, represented by yellow circles) during inflammation. Our custom-engineered EcN biosensor can detect NO using a NorR-based sensor (in purple) and subsequently trigger the production of nanobodies (in turquoise). These nanobodies are then released into the extracellular environment via a specially engineered secretion system in the bacterial host (shown in dark blue). Once outside the cell, the nanobodies attach to TNF, effectively sequestering them and reducing inflammation. The graph at the bottom of this panel illustrates the general behavior of our system: nanobody production starts upon reaching a certain NO concentration threshold and continues in an NO-dependent fashion. As nanobodies are produced, they capture TNF, leading to a reduction in inflammation and a decrease in NO production. This decrease in NO then halts the nanobody production. SignificanceProbiotics can be engineered to detect and act upon extracellular disease indicators, optimizing therapeutic outcomes. Particularly, self-regulating sense-and-respond genetic circuits have the potential to enhance the accuracy, efficacy, and adaptability of treatment interventions. In this study, we developed and characterized a new integrated and modular toolkit that detects a gut inflammation biomarker, specifically nitric oxide, and responds to it in an inducible manner by secreting humanized nanobodies targeting the pro-inflammatory molecule TNF. We also develop a coarse-grained mathematical framework for modelling engineered probiotic activity in the gut. This novel system contributes to current efforts to develop new engineered probiotic systems and holds promise for inspiring new treatments for gut inflammation associated with various autoimmune diseases.

synthetic biology↗

bioRxiv2023

The highly rugged yet navigable regulatory landscape of the bacterial transcription factor TetR

Transcription factor binding sites (TFBSs) are important sources of evolutionary innovations. Understanding how evolution navigates the sequence space of such sites can be achieved by mapping TFBS adaptive landscapes. In such a landscape, an individual location corresponds to a TFBS bound by a transcription factor. The elevation at that location corresponds to the strength of transcriptional regulation conveyed by the sequence. We developed an in vivo massively parallel reporter assay to map the landscape of bacterial TFBSs. We applied this assay to the TetR repressor, for which few TFBSs are known. We quantify the strength of transcriptional repression for 17,765 TFBSs and show that the resulting landscape is highly rugged, with 2,092 peaks. Only a few peaks convey stronger repression than the wild type. Non-additive (epistatic) interactions between mutations are frequent. Despite these hallmarks of ruggedness, most high peaks are evolutionarily accessible. They have large basins of attraction and are reached by around 20% of populations evolving on the landscape. Which high peak is reached during evolution is unpredictable and contingent on the mutational path taken. This first in-depth analysis of a prokaryotic gene regulator reveals a landscape that is navigable but much more rugged than the landscapes of eukaryotic regulators. SignificanceUnderstanding how evolution explores the vast space of genotypic possibilities is a fundamental question in evolutionary biology. The mapping of genotypes to quantitative traits (such as phenotypes and fitness) allows us to delineate adaptive landscapes and their topological properties, shedding light on how evolution can navigate such vast spaces. In this study, we focused on mapping a transcription factor binding site (TFBS) landscape to gene expression levels, as changes in gene expression patterns play a crucial role in biological innovation. We developed a massively parallel reporter assay and mapped the first comprehensive in vivo gene regulatory landscape for a bacterial transcriptional regulator, TetR. Surprisingly, this landscape is way more rugged than those observed in eukaryotic regulators. Despite its ruggedness, the landscape remains highly navigable through adaptive evolution. Our study presents the first high-resolution landscape for a bacterial TFBS, offering valuable insights into the evolution of TFBS in vivo. Moreover, it holds promise as a framework for discovering new genetic components for synthetic biological systems.

evolutionary biology↗

bioRxiv2017

Assessing and characterising the repertoire of constitutive promoter elements in soil metagenomic libraries in Escherichia coli

Although functional metagenomics has been widely employed for the discovery of genes relevant to biotechnology and biomedicine, its potential for assessing the diversity of transcriptional regulatory elements of microbial communities has remained poorly explored. Here, we have developed a novel framework for prospecting, characterising and estimating the accessibility of promoter sequences in metagenomic libraries by combining a bi-directional reporter vector, high-throughput fluorescence assays and predictive computational methods. Using the expression profiling of fluorescent clones from two independent libraries from soil samples, we directly analysed the regulatory dynamics of novel promoter elements, addressing the relationship between the \"metaconstitutome\" of a bacterial community and its environmental context. Through the construction and screening of plasmid-based metagenomic libraries followed by in silico analyses, we were able to provide both (i) a consensus exogenous promoter elements recognizable by Escherichia coli and (ii) an estimation of the accessible promoter sequences in a metagenomic library, which was close to 1% of the whole set of available promoters. The results presented here should provide new directions for the exploration through functional metagenomics of novel regulatory sequences in bacteria, which could expand the Synthetic Biology toolbox for novel biotechnological and biomedical applications.

microbiology↗

bioRxiv2017

Big trouble with little inserts: boundaries in metagenomic screenings using lacZα based vectors

The vast biochemical repertoire found in microbial communities from a wide-range of environments allows screening and isolation of novel enzymes with improved catalytic features. In this sense, metagenomics approaches have been of high relevance for providing enzymes used in diverse industrial applications. For instance, glycosyl hydrolases, which catalyze the hydrolysis of carbohydrates to sugars, are essential for bioethanol production from renewable resources. In the current study, we have focused on the prospection of protease and glycosyl hydrolase activities from microbial communities inhabiting a soil sample by using the lacZ-based plasmid pSEVA232 in the generation of a screenable metagenomic library. For this, we used a functional screen based on skimmed milk agar and a pH indicator dye as previously reported in literature. Although we effectively identified nine positive clones in the screenings, subsequent experiments revealed that this phenotype was not because of the hydrolytic activity encoded in the metagenomic fragments, but rather due to the insertion of small metagenomic DNA fragments in frame within the coding region of the lacZ alpha gene present in the original vector. We concluded that the current method has a higher tendency for false positive recovery of clones, when used in combination with a lacZ-based vector. Finally, we discuss the molecular explanation for positive phenotype recovering and highlight the importance of reporting boundaries in metagenomic screenings methodologies.

molecular biology↗