Fitness drift of an atrazine-degrading population under atrazine selection pressure

International audiencePseudomonas sp. ADP harbouring the atrazine catabolic plasmid ADP1 was subcultured in liquid medium containing atrazine as sole source of nitrogen. After approximately 320 generations, a new population evolved which replaced the initial population. This newly evolved population grew faster and degraded atrazine more rapidly than the initial population. Plasmid profiles and Southern blot analyses revealed that the evolved strain, unlike the ancestral strain, presented a tandem duplication of the atzB gene encoding the second enzyme of the atrazine catabolic pathway responsible for the transformation of hydroxyatrazine to N-isopropylammelide. This duplication resulted from a homologous recombination that occurred between two direct repeats of 6.2 kb flanking the atzB gene and constituted by the insertion sequences IS1071, ISPps1 and a pdhL homologous sequence. This study highlights the IS-mediated plasticity of atrazine-degrading potential and demonstrates that insertion sequences not only help to disperse the atrazine-degrading gene but also improve the fitness of the atrazine-degrading population

Verification of Concurrent Systems with VerCors

Abstract. This paper presents the VerCors approach to verification of concurrent software. It first discusses why verification of concurrent software is important, but also challenging. Then it shows how within the VerCors project we use permission-based separation logic to reason about multithreaded Java programs. We discuss in particular how we use the logic to use different implementations of synchronisers in verification, and how we reason about class invariance properties in a concurrent setting. Further, we also show how the approach is suited to reason about programs using a different concurrency paradigm, namely kernel programs using the Single Instruction Multiple Data paradigm. Concretely, we illustrate how permission-based separation logic is suitable to verify functional correctness properties of OpenCL kernels. All verification techniques discussed in this paper are supported by the VerCors tool set.