Biology subjects

Nyerges, A.

Publications and source records attributed to Nyerges, A..

14 recordsLinked to original sources

bioRxiv2026

Firewalled synthetic commensal blocks horizontal gene transfer in the gut

Synthetic biology enables the rational reprogramming of microorganisms into living therapeutics and agents for bioremediation. However, such genetically modified organisms (GMOs) disseminate their synthetic genetic information into natural microbial communities through horizontal gene transfer (HGT), posing biosafety risks that limit clinical and environmental deployment. Reassigning sense codons to an alternative amino acid identity establishes a genetic firewall that simultaneously prevents incoming and outgoing gene flow, but reported implementations compromise fitness, precluding clinical and industrial use. Here, we overcome this limitation using genome design and laboratory evolution to create a high-fitness genetically firewalled Escherichia coli commensal. By directly altering the amino acid identity of TCA and TCG serine codons in the genetic code without an unassigned intermediate, we establish a robust genetic firewall that remains stable for thousands of generations. This firewalled commensal stably colonizes the mouse gastrointestinal tract for more than 100 days and blocks viral infections and HGT. As the long-term within-gut evolution of this firewalled organism identified adaptive mutations in genes responsible for carbon source utilization, we rationally redesigned the strain's genome to increase fitness. Together, this work establishes a genetically firewalled commensal for safer living therapeutics development and provides a strategy for designing high-fitness, virus- and gene-transfer-resistant organisms for clinical and environmental use.

synthetic biology↗

bioRxiv2024

Synthetic genomes unveil the effects of synonymous recoding

Engineering the genetic code of an organism provides the basis for (i) making any organism safely resistant to natural viruses and (ii) preventing genetic information flow into and out of genetically modified organisms while (iii) allowing the biosynthesis of genetically encoded unnatural polymers1-4. Achieving these three goals requires the reassignment of multiple of the 64 codons nature uses to encode proteins. However, synonymous codon replacement--recoding--is frequently lethal, and how recoding impacts fitness remains poorly explored. Here, we explore these effects using whole-genome synthesis, multiplexed directed evolution, and genome-transcriptome-translatome-proteome co-profiling on multiple recoded genomes. Using this information, we assemble a synthetic Escherichia coli genome in seven sections using only 57 codons to encode proteins. By discovering the rules responsible for the lethality of synonymous recoding and developing a data-driven multi-omics-based genome construction workflow that troubleshoots synthetic genomes, we overcome the lethal effects of 62,007 synonymous codon swaps and 11,108 additional genomic edits. We show that synonymous recoding induces transcriptional noise including new antisense RNAs, leading to drastic transcriptome and proteome perturbation. As the elimination of select codons from an organisms genetic code results in the widespread appearance of cryptic promoters, we show that synonymous codon choice may naturally evolve to minimize transcriptional noise. Our work provides the first genome-scale description of how synonymous codon changes influence organismal fitness and paves the way for the construction of functional genomes that provide genetic firewalls from natural ecosystems and safely produce biopolymers, drugs, and enzymes with an expanded chemistry.

synthetic biology↗

bioRxiv2022

Swapped genetic code blocks viral infections and gene transfer

Removing cellular transfer RNAs (tRNAs), making their cognate codons unreadable, creates a genetic firewall that prevents viral replication and horizontal gene transfer. However, numerous viruses and mobile genetic elements encode parts of the translational apparatus, including tRNAs, potentially rendering a genetic-code-based firewall ineffective. In this paper, we show that such horizontally transferred tRNA genes can enable viral replication in Escherichia coli cells despite the genome-wide lack of three codons and the previously essential cognate tRNAs and release factor 1. By repurposing viral tRNAs, we then develop recoded cells bearing an amino-acid-swapped genetic code that reassigns two of the six serine codons to leucine during translation. This amino-acid-swapped genetic code renders cells completely resistant to viral infections by mistranslating viral proteomes and prevents the escape of synthetic genetic information by engineered reliance on serine codons to produce leucine-requiring proteins. Finally, we also repurpose the third free codon to biocontain this virus-resistant host via dependence on an amino acid not found in nature.

synthetic biology↗

bioRxiv2022

Strategies to Identify and Edit Improvements in Synthetic Genome Segments Episomally.

Genome engineering projects often utilize bacterial artificial chromosomes (BACs) to carry multi-kilobase DNA segments on low copy number vectors. However, DNA synthesis and amplification have the potential to impose mutations on the contained DNA segments that can in turn reduce or prevent viability of the final strain. Here, we describe improvements to a multiplex automated genome engineering (MAGE) protocol to improve recombineering frequency and multiplexability. This protocol was applied to recoding an Escherichia coli strain to swap out seven codons to synonymous alternatives genome-wide. Ten 44,402 to 47,179 bp de novo synthesized BAC-contained DNA segments from the recoded strain were unable to complement deletion of the corresponding 33 to 61 wild type genes using a single antibiotic resistance marker. Next-Generation Sequencing was used to identify 1-7 non-recoding mutations in essential genes per segment, and MAGE in turn proved a useful strategy to repair these mutations on the BAC-contained recoded segment when both the recoded and wild type copies of the mutated genes had to exist by necessity during the repair process. This strategy could be adapted to mutation identification and repair for other large-scale genome engineering projects, or for incorporation of small genetic engineering sites for quick protocol adjustments.

synthetic biology↗

bioRxiv2021

inPOSE: a flexible toolbox for chromosomal cloning and amplification of bacterial transgenes

Cloning genes and operons encoding heterologous functions in bacterial hosts is almost exclusively carried out today using plasmid vectors. This has multiple drawbacks, including the need for constant selection and the variation in copy numbers. Chromosomal integration of transgenes has always offered a viable alternative, however, to date it has been of limited use due to its tedious nature and to being limited often to a single copy. We introduce here a strategy that uses bacterial insertion sequences, the simplest autonomous transposable elements to insert and amplify genetic cargo into a bacterial chromosome. Transgene insertion can take place either as transposition or homologous recombination, and copy-number amplification is achieved using controlled copy-paste transposition. We display successful use of IS1 and IS3 for this purpose in Escherichia coli cells, using various selection markers. We demonstrate the insertion of selectable genes, an unselectable gene, and a five-gene operon in up to two copies in a single step. We continue with the amplification of the inserted cassette to double-digit copy numbers within two rounds of transposase induction and selection. Finally, we analyze the stability of the cloned genetic constructs in the lack of selection and find it to be superior to all investigated plasmid-based systems. Due to the ubiquitous nature of transposable elements, we believe that with proper design, this strategy can be adapted to numerous further bacterial species.

molecular biology↗

bioRxiv2021

ssDNA recombineering boosts in vivo evolution of nanobodies displayed on bacterial surfaces

In vivo evolution of antibodies facilitates emergence of novel target specificities from pre-existing clones. In this work we show how mutagenic ssDNA recombineering of camel-derived nanobodies encoded in a bacterial genome enables clonal hyper-diversification and the rise of new properties. As a proof-of-principle we used a nanobody recognizing the antigen TirM from enterohaemorrhagic E. coli (EHEC) and evolved it towards the otherwise not recognized TirM antigen from enteropathogenic E. coli (EPEC). To this end, E. coli cells displaying on their surface this nanobody fused to the intimin outer membrane anchor domain were subjected to multiple rounds of mutagenic ssDNA recombineering targeted to the CDR1, CDR2 and CDR3 regions of its genomically encoded VHH sequence. Binders to the new antigen (EPEC TirM) were then selected upon immunomagnetic capture of bacteria bearing the corresponding nanobody variants. As a result, several modified nanobodies were identified which maintained recognition of EHEC TirM but acquired the ability to bind the new antigen with high affinity (Kd ~20 nM). The results highlight the power of combining evolutionary properties of bacteria in vivo with oligonucleotide synthesis in vitro for the sake of focusing diversification to specific segments of a gene (or protein thereof) of interest. Our experimental workflow empowers the evolution of nanobodies displayed on the surface of bacterial cells for a large number of potential applications in medical and industrial biotechnology.

synthetic biology↗

bioRxiv2020

Improved bacterial recombineering by parallelized protein discovery

Exploiting bacteriophage-derived homologous recombination processes has enabled precise, multiplex editing of microbial genomes and the construction of billions of customized genetic variants in a single day. The techniques that enable this, Multiplex Automated Genome Engineering (MAGE) and directed evolution with random genomic mutations (DIvERGE), are however currently limited to a handful of microorganisms for which single-stranded DNA-annealing proteins (SSAPs) that promote efficient recombineering have been identified. Thus, to enable genome-scale engineering in new hosts, highly efficient SSAPs must first be found. Here we introduce a high-throughput method for SSAP discovery that we call Serial Enrichment for Efficient Recombineering (SEER). By performing SEER in E. coli to screen hundreds of putative SSAPs, we identify highly active variants PapRecT and CspRecT. CspRecT increases the efficiency of single-locus editing to as high as 50% and improves multiplex editing by 5 to 10-fold in E. coli, while PapRecT enables efficient recombineering in Pseudomonas aeruginosa, a concerning human pathogen. CspRecT and PapRecT are also active in other, clinically and biotechnologically relevant enterobacteria. We envision that the deployment of SEER in new species will pave the way toward pooled interrogation of genotype-to-phenotype relationships in previously intractable bacteria.

microbiology↗

bioRxiv2019

High-efficiency multi-site genomic editing (HEMSE) of Pseudomonas putida through thermoinducible ssDNA recombineering

While single-stranded DNA recombineering is a powerful strategy for higher-scale genome editing, its application to species other than enterobacteria is typically limited by the efficiency of the recombinase and the action of native mismatch repair (MMR) systems. By building on [i] availability of the Erf-like single-stranded DNA-annealing protein Rec2, [ii] adoption of tightly-regulated thermoinducible device and [iii] transient expression of a MMR-supressing mutL allele, we have set up a coherent genetic platform for entering multiple changes in the chromosome of Pseudomononas putida with an unprecedented efficacy and reliability. The key genetic construct to this end is a broad host range plasmid encoding co-transcription of rec2 and P. putidas mutLE36KPP at high levels under the control of the PL/cI857 system. Cycles of short thermal shifts of P. putida cells followed by transformation with a suite of mutagenic oligos delivered different types of high-fidelity genomic changes at frequencies up to 10% per single change--that can be handled without selection. The same approach was instrumental to super-diversify short chromosomal portions for creating libraries of functional genomic segments--as shown in this case with ribosomal binding sites. These results enable the multiplexing of genome engineering of P. putida, as required for metabolic engineering of this important biotechnological chassis.

microbiology↗

bioRxiv2019

Multiple-site diversification of regulatory sequences enables inter-species operability of genetic devices

The features of the light-responsive cyanobacterial CcaSR regulatory node that determine interoperability of this optogenetic device between Escherichia coli and Pseudomonas putida have been examined. For this, all structural parts (i.e. ho1 and pcyA genes for synthesis of phycobilin, the ccaS/ccaR system from Synechocystis and its cognate downstream promoter) were maintained but their expression levels and stoichiometry diversified by [i] reassembling them together in a single broad host range, standardized vector and [ii] subjecting the non-coding regulatory sequences to multiple cycles of directed evolution with random genomic mutations (DIvERGE), a recombineering method that intensifies mutation rates within discrete DNA segments. Once passed to P. putida, various clones displayed a wide dynamic range, insignificant leakiness and excellent capacity in response to green light. Inspection of the evolutionary intermediates pinpointed translational control as the main bottleneck for interoperability and suggested a general approach for easing the exchange of genetic cargoes between different species i.e. optimization of relative expression levels and upturning of subcomplex stoichiometry.

synthetic biology↗

bioRxiv2019

Mismatch repair hierarchy of Pseudomonas putida revealed by mutagenic ssDNA recombineering of the pyrF gene

The mismatch repair (MMR) system is one of the key molecular devices that prokaryotic cells have for ensuring fidelity of DNA replication. While the canonical MMR of E. coli involves 3 proteins (encoded by mutS, mutL and mutH), the soil bacterium Pseudomonads putida has only 2 bona fide homologues (mutS and mutL) and the sensitivity of this abridged system to different types of mismatches is unknown. On this background, sensitivity to MMR of this bacterium was inspected through single stranded (ss) DNA recombineering of the pyrF gene (the prokaryotic equivalent to yeasts URA3) with mutagenic oligos representative of every possible mispairing under either wild-type conditions, permanent deletion of mutS or transient loss of mutL activity (brought about by the thermoinducible dominant negative allele mutLE36K). Analysis of single nucleotide mutations borne by clones resistant to fluoroorotic acid (5FOA, the target of wild type PyrF) pinpointed prohibited and tolerated single-nucleotide replacements and exposed a clear grading of mismatch recognition. The resulting data unequivocally established the hierarchy A:G< C:C< G:A< C:A, A:A, G:G, T:T, T:G, A:C, C:T< G:T, T:C as the one prevalent in Pseudomonas putida. This information was vital for enabling recombineering strategies aimed at single-nucleotide changes in this biotechnologically important species.\n\nOriginality-Significance StatementSingle-stranded DNA (ssDNA) recombineering has emerged in recent years as one of the most powerful technologies of genome editing in E. coli and other Enterobacteria. However, the efforts to expand the concept and the methods towards environmental microorganisms such as Pseudomonas putida have been limited thus far by several gaps in our fundamental knowledge of how nucleotide mismatch repair (MMR) operates in such non-model species. One critical bottleneck is the hierarchy of recognition of different types of base mispairings as well as the need of setting up strategies for counteracting MMR and thus enabling tolerance to all types of changes. The work presented here tackles both issues and makes P. putida amenable to sophisticated genetic manipulations that were impossible before.

microbiology↗

bioRxiv2018

Antibiotic usage promotes the evolution of resistance against gepotidacin, a novel multi-targeting drug

Multi-targeting antibiotics, i.e. single compounds capable to inhibit two or more bacterial targets offer a promising therapeutic strategy, but information on resistance evolution against such drugs is scarce. Gepotidacin is an antibiotic candidate that selectively inhibits both bacterial DNA gyrase and topoisomerase IV. In a susceptible organism, Klebsiella pneumoniae, a combination of two specific mutations in these target proteins provide an over 2000-fold increment in resistance, while individually none of these mutations affect resistance significantly. Alarmingly, gepotidacin-resistant strains are found to be as virulent as the wild-type K. pneumoniae strain in a murine model, and extensive cross-resistance was demonstrated between gepotidacin and ciprofloxacin, a fluoroquinolone antibiotic widely employed in clinical practice. This suggests that numerous fluoroquinolone-resistant pathogenic isolates carry mutations which would promote the evolution of clinically significant resistance against gepotidacin in the future. We conclude that prolonged antibiotic usage could select for mutations that serve as stepping-stones towards resistance against antimicrobial compounds still under development. More generally, our research indicates that even balanced multi-targeting antibiotics are prone to resistance evolution.

microbiology↗

bioRxiv2018

CRISPR-interference based modulation of mobile genetic elements in bacteria

Spontaneous mutagenesis of synthetic genetic constructs by mobile genetic elements frequently results in the rapid loss of advantageous functions. Previous efforts to minimize such mutations required the exceedingly time-consuming manipulation of bacterial chromosomes and the complete removal of insertional sequences (ISes). To this aim, we developed a single plasmid-based system (pCRIS) that applies CRISPR-interference to inhibit the transposition of bacterial ISes. pCRIS expresses multiple guide RNAs to direct inactivated Cas9 (dCas9) to simultaneously silence IS1, IS3, IS5, and IS150 at up to 38 chromosomal loci in Escherichia coli, in vivo. As a result, the transposition rate of all four targeted ISes dropped to negligible levels at both chromosomal and episomal targets, increasing the half-life of exogenous protein expression. Most notably, pCRIS, while requiring only a single plasmid delivery performed within a single day, provided a reduction of IS-mobility comparable to that seen in genome-scale chromosome engineering projects. Global transcriptomics analysis revealed nevertheless only minute alterations in the expression of untargeted genes. Finally, the transposition-silencing effect of pCRIS was easily transferable across multiple E. coli strains. The plasticity and robustness of our IS-silencing system make it a promising tool to stabilize bacterial genomes for synthetic biology and industrial biotechnology applications.

synthetic biology↗

bioRxiv2018

Phylogenetic barriers to horizontal transfer of antimicrobial peptide resistance genes in the human gut microbiota

The human gut microbiota has adapted to the presence of antimicrobial peptides (AMPs) that are ancient components of immune defence. Despite important medical relevance, it has remained unclear whether AMP resistance genes in the gut microbiome are available for genetic exchange between bacterial species. Here we show that AMP- and antibiotic-resistance genes differ in their mobilization patterns and functional compatibilities with new bacterial hosts. First, whereas AMP resistance genes are widespread in the gut microbiome, their rate of horizontal transfer is lower than that of antibiotic resistance genes. Second, gut microbiota culturing and functional metagenomics revealed that AMP resistance genes originating from phylogenetically distant bacteria only have a limited potential to confer resistance in Escherichia coli, an intrinsically susceptible species. Third, the phenotypic impact of acquired AMP resistance genes heavily depends on the genetic background of the recipient bacteria. Taken together, functional compatibility with the new bacterial host emerges as a key factor limiting the genetic exchange of AMP resistance genes. Finally, our results suggest that AMPs induce highly specific changes in the composition of the human microbiota with implications for disease risks.

microbiology↗

bioRxiv2018

Enzyme promiscuity shapes evolutionary innovation and optimization

Evidence suggests that novel enzyme functions evolved from low-level promiscuous activities in ancestral enzymes. Yet, the evolutionary dynamics and physiological mechanisms of how such side activities contribute to systems-level adaptations are poorly understood. Furthermore, it remains untested whether knowledge of an organisms promiscuous reaction set ( underground metabolism) can aid in forecasting the genetic basis of metabolic adaptations. Here, we employ a computational model of underground metabolism and laboratory evolution experiments to examine the role of enzyme promiscuity in the acquisition and optimization of growth on predicted non-native substrates in E. coli K-12 MG1655. After as few as 20 generations, the evolving populations repeatedly acquired the capacity to grow on five predicted novel substrates-D-lyxose, D-2-deoxyribose, D-arabinose, m-tartrate, and monomethyl succinate-none of which could support growth in wild-type cells. Promiscuous enzyme activities played key roles in multiple phases of adaptation. Altered promiscuous activities not only established novel high-efficiency pathways, but also suppressed undesirable metabolic routes. Further, structural mutations shifted enzyme substrate turnover rates towards the new substrate while retaining a preference for the primary substrate. Finally, genes underlying the phenotypic innovations were accurately predicted by genome-scale model simulations of metabolism with enzyme promiscuity. Computational approaches will be essential to synthesize the complex role of promiscuous activities in applied biotechnology and in models of evolutionary adaptation.

systems biology↗