Systematic genome engineering approaches to investigate mutational effects and evolutionary processes

To address the shortcomings of currently available genome editing and in vivo directed evolution techniques, we have developed a plasmid-based method for broad-host-range genome engineering (pORTMAGE), and based on pORTMAGE, a method for in vivo directed evolution. This new method, termed DIvERGE (directed evolution with random genomic mutations) allows the systematic multiplex mutagenesis of long genomic segments. DIvERGE has numerous advantages over the alternative techniques, including (I) the possibility to target multiple, user-defined genomic regions; (II) it has a broad and controllable mutagenesis spectrum for each nucleotide position; (III) it allows of up to a million-fold increase in mutation rate at the target sequence; (IV) it enables multiple rounds of mutagenesis and selection in a fast and continuous manner; (V) it is applicable to a wide range of enterobacterial species without the need for prior genomic modification(s); (VI) it avoids off-target mutagenesis, and (VII) it is also cost-effective as it relies on soft-randomized oligos which can easily be manufactured at a modest cost. In summary, DIvERGE offers a versatile solution for high-precision directed evolution at multiple loci in their native genomic context. Due to these favorable characteristics, DIvERGE is especially well-suited to study bacterial evolution leading to antibiotic resistance

Conditional DNA repair mutants enable highly precise genome engineering

Oligonucleotide-mediated multiplex genome engineering is an important tool for bacterial genome editing. The efficient application of this technique requires the inactivation of the endogenous methyl-directed mismatch repair system that in turn leads to a drastically elevated genomic mutation rate and the consequent accumulation of undesired off-target mutations. Here, we present a novel strategy for mismatch repair evasion using temperature-sensitive DNA repair mutants and temporal inactivation of the mismatch repair protein complex in Escherichia coli. Our method relies on the transient suppression of DNA repair during mismatch carrying oligonucleotide integration. Using temperature-sensitive control of methyl-directed mismatch repair protein activity during multiplex genome engineering, we reduced the number of off-target mutations by 85%, concurrently maintaining highly efficient and unbiased allelic replacement

Perturbation of iron homeostasis promotes the evolution of antibiotic resistance.

Evolution of antibiotic resistance in microbes is frequently achieved by acquisition of spontaneous mutations during antimicrobial therapy. Here, we demonstrate that inactivation of a central transcriptional regulator of iron homeostasis (Fur) facilitates laboratory evolution of ciprofloxacin resistance in Escherichia coli. To decipher the underlying molecular mechanisms, we first performed a global transcriptome analysis and demonstrated that the set of genes regulated by Fur changes substantially in response to antibiotic treatment. We hypothesized that the impact of Fur on evolvability under antibiotic pressure is due to the elevated intracellular concentration of free iron and the consequent enhancement of oxidative damage-induced mutagenesis. In agreement with expectations, overexpression of iron storage proteins, inhibition of iron transport, or anaerobic conditions drastically suppressed the evolution of resistance, whereas inhibition of the SOS response-mediated mutagenesis had only a minor effect. Finally, we provide evidence that a cell permeable iron chelator inhibits the evolution of resistance. In sum, our work revealed the central role of iron metabolism in the de novo evolution of antibiotic resistance, a pattern that could influence the development of novel antimicrobial strategies

High-Efficiency Multi-site Genomic Editing of Pseudomonas putida through Thermoinducible ssDNA Recombineering

Application of single-stranded DNA recombineering for genome editing of species other than enterobacteria is limited by the efficiency of the recombinase and the action of endogenous mismatch repair (MMR) systems. In this work we have set up a genetic system for entering multiple changes in the chromosome of the biotechnologically relevant strain EM42 of Pseudomononas putida. To this end high-level heat-inducible co-transcription of the rec2 recombinase and P. putida's allele mutL(E36K)(PP) was designed under the control of the P-L/cl857 system. Cycles of short thermal shifts followed by transformation with a suite of mutagenic oligos delivered different types of genomic changes at frequencies up to 10% per single modification. The same approach was instrumental to super-diversify short chromosomal portions for creating libraries of functional genomic segments-e.g., ribosomal-binding sites. These results enabled multiplexing of genome engineering of P. putida, as required for metabolic reprogramming of this important synthetic biology chassis

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. In this background, sensitivity to MMR of this bacterium was inspected through single stranded (ss) DNA recombineering of the pyrF gene (the prokaryotic equivalent to yeast's 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 mutL(E36K)). 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 is vital for enabling recombineering strategies aimed at single-nucleotide changes in this biotechnologically important species

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 engineered 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. 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. The fitness cost of multiple IS-knockdown, detectable in flask-and-shaker systems was readily outweighed by the less frequent inactivation of the transgene, as observed in green fluorescent protein (GFP)-overexpression experiments. In addition, global transcriptomics analysis revealed 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

New N-phenylpyrrolamide DNA gyrase B inhibitors: Optimization of efficacy and antibacterial activity

The ATP binding site located on the subunit B of DNA gyrase is an attractive target for the development of new antibacterial agents. In recent decades, several small-molecule inhibitor classes have been discovered but none has so far reached the market. We present here the discovery of a promising new series of N-phenylpyrrolamides with low nanomolar IC50 values against DNA gyrase, and submicromolar IC50 values against topoisomerase IV from Escherichia coil and Staphylococcus aureus. The most potent compound in the series has an IC50 value of 13 nM against E. coil gyrase. Minimum inhibitory concentrations (MICs) against Gram-positive bacteria are in the low micromolar range. The oxadiazolone derivative with an IC50 value of 85 nM against E. coli DNA gyrase displays the most potent antibacterial activity, with MIC values of 1.56 mu M against Enterococcus faecalis, and 3.13 mu M against wild type S. aureus, methicillinresistant S. aureus (MRSA) and vancomycin-resistant Enterococcus (VRE). The activity against wild type E. coli in the presence of efflux pump inhibitor phenylalanine-arginine beta-naphthylamide (PA beta N) is 4.6 mu M. (C) 2018 Elsevier Masson SAS. All rights reserved

New N-phenylpyrrolamide DNA gyrase B inhibitors: Optimization of efficacy and antibacterial activity

The ATP binding site located on the subunit B of DNA gyrase is an attractive target for the development of new antibacterial agents. In recent decades, several small-molecule inhibitor classes have been discovered but none has so far reached the market. We present here the discovery of a promising new series of N-phenylpyrrolamides with low nanomolar IC50 values against DNA gyrase, and submicromolar IC50 values against topoisomerase IV from Escherichia coil and Staphylococcus aureus. The most potent compound in the series has an IC50 value of 13 nM against E. coil gyrase. Minimum inhibitory concentrations (MICs) against Gram-positive bacteria are in the low micromolar range. The oxadiazolone derivative with an IC50 value of 85 nM against E. coli DNA gyrase displays the most potent antibacterial activity, with MIC values of 1.56 mu M against Enterococcus faecalis, and 3.13 mu M against wild type S. aureus, methicillinresistant S. aureus (MRSA) and vancomycin-resistant Enterococcus (VRE). The activity against wild type E. coli in the presence of efflux pump inhibitor phenylalanine-arginine beta-naphthylamide (PA beta N) is 4.6 mu M. (C) 2018 Elsevier Masson SAS. All rights reserved.Peer reviewe