Professional Education

  • Doctor of Philosophy, Universite de Paris V (Rene Descartes) (2016)
  • Doctor of Pharmacy, Universite de Paris V (Rene Descartes), Pharmacy (2015)
  • Master of Science, Universite de Paris V (Rene Descartes) (2012)

Lab Affiliations

All Publications

  • Differences in Integron Cassette Excision Dynamics Shape a Trade-Off between Evolvability and Genetic Capacitance MBIO Loot, C., Nivina, A., Cury, J., Escudero, J. A., Ducos-Galand, M., Bikard, D., Rocha, E. P., Mazel, D. 2017; 8 (2)


    Integrons ensure a rapid and "on demand" response to environmental stresses driving bacterial adaptation. They are able to capture, store, and reorder functional gene cassettes due to site-specific recombination catalyzed by their integrase. Integrons can be either sedentary and chromosomally located or mobile when they are associated with transposons and plasmids. They are respectively called sedentary chromosomal integrons (SCIs) and mobile integrons (MIs). MIs are key players in the dissemination of antibiotic resistance genes. Here, we used in silico and in vivo approaches to study cassette excision dynamics in MIs and SCIs. We show that the orientation of cassette arrays relative to replication influences attC site folding and cassette excision by placing the recombinogenic strands of attC sites on either the leading or lagging strand template. We also demonstrate that stability of attC sites and their propensity to form recombinogenic structures also regulate cassette excision. We observe that cassette excision dynamics driven by these factors differ between MIs and SCIs. Cassettes with high excision rates are more commonly found on MIs, which favors their dissemination relative to SCIs. This is especially true for SCIs carried in the Vibrio genus, where maintenance of large cassette arrays and vertical transmission are crucial to serve as a reservoir of adaptive functions. These results expand the repertoire of known processes regulating integron recombination that were previously established and demonstrate that, in terms of cassette dynamics, a subtle trade-off between evolvability and genetic capacitance has been established in bacteria.IMPORTANCE The integron system confers upon bacteria a rapid adaptation capability in changing environments. Specifically, integrons are involved in the continuous emergence of bacteria resistant to almost all antibiotic treatments. The international situation is critical, and in 2050, the annual number of deaths caused by multiresistant bacteria could reach 10 million, exceeding the incidence of deaths related to cancer. It is crucial to increase our understanding of antibiotic resistance dissemination and therefore integron recombination dynamics to find new approaches to cope with the worldwide problem of multiresistance. Here, we studied the dynamics of recombination and dissemination of gene encoding cassettes carried on integrons. By combining in silico and in vivo analyses, we show that cassette excision is highly regulated by replication and by the intrinsic properties of cassette recombination sites. We also demonstrated differences in the dynamics of cassette recombination between mobile and sedentary chromosomal integrons (MIs and SCIs). For MIs, a high cassette recombination rate is favored and timed to conditions when generating diversity (upon which selection can act) allows for a rapid response to environmental conditions and stresses. In contrast, for SCIs, cassette excisions are less frequent, limiting cassette loss and ensuring a large pool of cassettes. We therefore confirm a role of SCIs as reservoirs of adaptive functions and demonstrate that the remarkable adaptive success of integron recombination system is due to its intricate regulation.

    View details for DOI 10.1128/mBio.02296-16

    View details for Web of Science ID 000400575700039

    View details for PubMedID 28351923

    View details for PubMedCentralID PMC5371416

  • Recoding of synonymous genes to expand evolutionary landscapes requires control of secondary structure affecting translation. Biotechnology and bioengineering Escudero, J. A., Nivina, A., Cambray, G., L√≥pez-Igual, R., Loot, C., Mazel, D. 2017


    Synthetic DNA design needs to harness the many information layers embedded in a DNA string. We previously developed the Evolutionary Landscape Painter (ELP), an algorithm that exploits the degeneracy of the code to increase protein evolvability. Here, we have used ELP to recode the integron integrase gene (intI1) in two alternative alleles. Although synonymous, both alleles yielded less IntI1 protein and were less active in recombination assays than intI1. We spliced the three alleles and mapped the activity decrease to the beginning of alternative sequences. Mfold predicted the presence of more stable secondary structures in the alternative genes. Using synonymous mutations, we decreased their stability and recovered full activity. Following a design-build-test approach, we have now updated ELP to consider such structures and provide streamlined alternative sequences. Our results support the possibility of modulating gene activity through the ad hoc design of 5' secondary structures in synthetic genes. This article is protected by copyright. All rights reserved.

    View details for DOI 10.1002/bit.26450

    View details for PubMedID 28898391

  • Efficiency of integron cassette insertion in correct orientation is ensured by the interplay of the three unpaired features of attC recombination sites NUCLEIC ACIDS RESEARCH Nivina, A., Escudero, J. A., Vit, C., Mazel, D., Loot, C. 2016; 44 (16): 7792-7803


    The integron is a bacterial recombination system that allows acquisition, stockpiling and expression of cassettes carrying protein-coding sequences, and is responsible for the emergence and rise of multiresistance in Gram-negative bacteria. The functionality of this system depends on the insertion of promoterless cassettes in correct orientation, allowing their expression from the promoter located upstream of the cassette array. Correct orientation is ensured by strand selectivity of integron integrases for the bottom strand of cassette recombination sites (attC), recombined in form of folded single-stranded hairpins. Here, we investigated the basis of such strand selectivity by comparing recombination of wild-type and mutated attC sites with different lengths, sequences and structures. We show that all three unpaired structural features that distinguish the bottom and top strands contribute to strand selectivity. The localization of Extra-Helical Bases (EHBs) directly favors integrase binding to the bottom strand. The Unpaired Central Spacer (UCS) and the Variable Terminal Structure (VTS) influence strand selectivity indirectly, probably through the stabilization of the bottom strand and the resulting synapse due to the nucleotide skew between the two strands. These results underscore the importance of the single-stranded nature of the attC site that allows such tight control over integron cassette orientation.

    View details for DOI 10.1093/nar/gkw646

    View details for Web of Science ID 000384687000027

    View details for PubMedID 27496283

    View details for PubMedCentralID PMC5027507

  • Unmasking the ancestral activity of integron integrases reveals a smooth evolutionary transition during functional innovation NATURE COMMUNICATIONS Escudero, J. A., Loot, C., Parissi, V., Nivina, A., Bouchier, C., Mazel, D. 2016; 7


    Tyrosine (Y)-recombinases have evolved to deliver mechanistically different reactions on a variety of substrates, but these evolutionary transitions are poorly understood. Among them, integron integrases are hybrid systems recombining single- and double-stranded DNA partners. These reactions are asymmetric and need a replicative resolution pathway, an exception to the canonical second strand exchange model of Y-recombinases. Integron integrases possess a specific domain for this specialized pathway. Here we show that despite this, integrases are still capable of efficiently operating the ancestral second strand exchange in symmetrical reactions between double-stranded substrates. During these reactions, both strands are reactive and Holliday junction resolution can follow either pathway. A novel deep-sequencing approach allows mapping of the crossover point for the second strand exchange. The persistence of the ancestral activity in integrases illustrates their robustness and shows that innovation towards new recombination substrates and resolution pathways was a smooth evolutionary process.

    View details for DOI 10.1038/ncomms10937

    View details for Web of Science ID 000371737500001

    View details for PubMedID 26961432

    View details for PubMedCentralID PMC4792948

  • The Integron: Adaptation On Demand. Microbiology spectrum Escudero, J. A., Loot, C., Nivina, A., Mazel, D. 2015; 3 (2): MDNA3-0019 2014


    The integron is a powerful system which, by capturing, stockpiling, and rearranging new functions carried by gene encoding cassettes, confers upon bacteria a rapid adaptation capability in changing environments. Chromosomally located integrons (CI) have been identified in a large number of environmental Gram-negative bacteria. Integron evolutionary history suggests that these sedentary CIs acquired mobility among bacterial species through their association with transposable elements and conjugative plasmids. As a result of massive antibiotic use, these so-called mobile integrons are now widespread in clinically relevant bacteria and are considered to be the principal agent in the emergence and rise of antibiotic multiresistance in Gram-negative bacteria. Cassette rearrangements are catalyzed by the integron integrase, a site-specific tyrosine recombinase. Central to these reactions is the single-stranded DNA nature of one of the recombination partners, the attC site. This makes the integron a unique recombination system. This review describes the current knowledge on this atypical recombination mechanism, its implications in the reactions involving the different types of sites, attC and attI, and focuses on the tight regulation exerted by the host on integron activity through the control of attC site folding. Furthermore, cassette and integrase expression are also highly controlled by host regulatory networks and the bacterial stress (SOS) response. These intimate connections to the host make the integron a genetically stable and efficient system, granting the bacteria a low cost, highly adaptive evolution potential "on demand".

    View details for DOI 10.1128/microbiolspec.MDNA3-0019-2014

    View details for PubMedID 26104695