title: Co-selection and replacement of resistance alleles to Lysinibacillus sphaericus in a Culex quinquefasciatus colony.
abstract: The Cqm1 α-glucosidase, expressed within the midgut of Culex quinquefasciatus mosquito larvae, is the receptor for the Binary toxin (Bin) from the entomopathogen Lysinibacillus sphaericus. Mutations of the Cqm1 α-glucosidase gene cause high resistance levels to this bacterium in both field and laboratory populations, and a previously described allele, cqm1REC, was found to be associated with a laboratory-resistant colony (R2362). This study described the identification of a novel resistance allele, cqm1REC-2, that was co-selected with cqm1REC within the R2362 colony. The two alleles display distinct mutations but both generate premature stop codons that prevent the expression of midgut-bound Cqm1 proteins. Using a PCR-based assay to monitor the frequency of each allele during long-term maintenance of the resistant colony, cqm1REC was found to predominate early on but later was replaced by cqm1REC-2 as the most abundant resistance allele. Homozygous larvae for each allele were then generated that displayed similar high-resistance phenotypes with equivalent low levels of transcript and lack of protein expression for both cqm1REC and cqm1REC-2. In progeny from a cross of homozygous individuals for each allele at a 1 : 1 ratio, analyzed for ten subsequent generations, cqm1REC showed a higher frequency than cqm1REC-2. The replacement of cqm1REC by cqm1REC -2 observed in the R2362 colony, kept for 210 generations, indicates changes in fitness related to traits that are unknown but linked to these two alleles, and constitutes a unique example of evolution of resistance within a controlled laboratory environment.
authors.affiliation: Department of Entomology, Centro de Pesquisas Aggeu Magalhães, FIOCRUZ, Recife, Brazil.
authors.forename: Karlos Diogo de Melo
authors.initials: KD
authors.lastname: Chalegre
authors.affiliation: Department of Entomology, Centro de Pesquisas Aggeu Magalhães, FIOCRUZ, Recife, Brazil.
authors.forename: Daniella A
authors.initials: DA
authors.lastname: Tavares
authors.affiliation: Department of Entomology, Centro de Pesquisas Aggeu Magalhães, FIOCRUZ, Recife, Brazil.
authors.forename: Tatiany P
authors.initials: TP
authors.lastname: Romão
authors.affiliation: Department of Entomology, Centro de Pesquisas Aggeu Magalhães, FIOCRUZ, Recife, Brazil.
authors.forename: Heverly Suzany G
authors.initials: HS
authors.lastname: de Menezes
authors.affiliation: Department of Entomology, Centro de Pesquisas Aggeu Magalhães, FIOCRUZ, Recife, Brazil.
authors.forename: Nathaly A
authors.initials: NA
authors.lastname: Nascimento
authors.affiliation: Department of Entomology, Centro de Pesquisas Aggeu Magalhães, FIOCRUZ, Recife, Brazil.
authors.forename: Cláudia Maria F
authors.initials: CM
authors.lastname: de Oliveira
authors.affiliation: Department of Microbiology, Centro de Pesquisas Aggeu Magalhães, FIOCRUZ, Recife, Brazil.
authors.forename: Osvaldo P
authors.initials: OP
authors.lastname: de-Melo-Neto
authors.affiliation: Department of Entomology, Centro de Pesquisas Aggeu Magalhães, FIOCRUZ, Recife, Brazil.
authors.forename: Maria Helena N L
authors.initials: MH
authors.lastname: Silva-Filha
mesh_terms: D000818:Animals; D001406:Bacillaceae / Q000472:pathogenicity*; D001427:Bacterial Toxins / Q000378:metabolism / Q000633:toxicity; D003433:Crosses, Genetic; D003465:Culex / Q000201:enzymology / Q000235:genetics* / Q000382:microbiology*; D019143:Evolution, Molecular; D005260:Female; D005787:Gene Frequency; D017344:Genes, Insect; D016908:Gram-Positive Bacterial Infections / Q000235:genetics / Q000382:microbiology; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism; D007814:Larva / Q000201:enzymology / Q000235:genetics / Q000382:microbiology; D008297:Male; D009154:Mutation; D012641:Selection, Genetic; D000520:alpha-Glucosidases / Q000235:genetics / Q000378:metabolism
chemical_list: D001427:Bacterial Toxins; D019476:Insect Proteins; C046134:binB protein, Bacillus sphaericus; D000520:alpha-Glucosidases
keywords: Binary toxin; allele replacement; cqm1 alleles; receptors; α-glucosidases