title: Mechanism behind Resistance against the Organophosphate Azamethiphos in Salmon Lice (Lepeophtheirus salmonis).
abstract: Acetylcholinesterase (AChE) is the primary target for organophosphates (OP). Several mutations have been reported in AChE to be associated with the reduced sensitivity against OP in various arthropods. However, to the best of our knowledge, no such reports are available for Lepeophtheirus salmonis. Hence, in the present study, we aimed to determine the association of AChE(s) gene(s) with resistance against OP. We screened the AChE genes (L. salmonis ace1a and ace1b) in two salmon lice populations: one sensitive (n=5) and the other resistant (n=5) for azamethiphos, a commonly used OP in salmon farming. The screening led to the identification of a missense mutation Phe362Tyr in L. salmonis ace1a, (corresponding to Phe331 in Torpedo californica AChE) in all the samples of the resistant population. We confirmed the potential role of the mutation, with reduced sensitivity against azamethiphos in L. salmonis, by screening for Phe362Tyr in 2 sensitive and 5 resistant strains. The significantly higher frequency of the mutant allele (362Tyr) in the resistant strains clearly indicated the possible association of Phe362Tyr mutation in L. salmonis ace1a with resistance towards azamethiphos. The 3D modelling, short term survival experiments and enzymatic assays further supported the imperative role of Phe362Tyr in reduced sensitivity of L. salmonis for azamethiphos. Based on all these observations, the present study, for the first time, presents the mechanism of resistance in L. salmonis against azamethiphos. In addition, we developed a rapid diagnostic tool for the high throughput screening of Phe362Tyr mutation using High Resolution Melt analysis.
authors.affiliation: NMBU School of Veterinary Science, Sea Lice Research Centre, PO Box 8146 Dep., NO-0033 Oslo, Norway.
authors.forename: Kiranpreet
authors.initials: K
authors.lastname: Kaur
authors.affiliation: NMBU School of Veterinary Science, Sea Lice Research Centre, PO Box 8146 Dep., NO-0033 Oslo, Norway.
authors.forename: Kari Olli
authors.initials: KO
authors.lastname: Helgesen
authors.affiliation: NMBU School of Veterinary Science, Sea Lice Research Centre, PO Box 8146 Dep., NO-0033 Oslo, Norway.
authors.forename: Marit Jørgensen
authors.initials: MJ
authors.lastname: Bakke
authors.affiliation: NMBU School of Veterinary Science, Sea Lice Research Centre, PO Box 8146 Dep., NO-0033 Oslo, Norway.
authors.forename: Tor Einar
authors.initials: TE
authors.lastname: Horsberg
mesh_terms: D000483:Alleles; D000818:Animals; D001483:Base Sequence; D001681:Biological Assay; D003062:Codon; D003445:Crustacea / Q000235:genetics*; D004351:Drug Resistance / Q000235:genetics*; D005260:Female; D005838:Genotype; D006720:Homozygote; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D010755:Organophosphates / Q000737:chemistry*; D063086:Organothiophosphates / Q000737:chemistry; D010641:Phenotype; D011110:Polymorphism, Genetic; D012474:Salmon / Q000469:parasitology; D012689:Sequence Homology, Nucleic Acid
chemical_list: D003062:Codon; D010755:Organophosphates; D063086:Organothiophosphates; C072763:azamethiphos