title: Single nucleotide deletion of cqm1 gene results in the development of resistance to Bacillus sphaericus in Culex quinquefasciatus.
abstract: The entomopathogen Bacillus sphaericus is one of the most effective biolarvicides used to control the Culex species of mosquito. The appearance of resistance in mosquitoes to this bacterium, however, remains a threat to its continuous use in integrated mosquito control programs. Previous work showed that the resistance to B. sphaericus in Culex colonies was associated with the absence of the 60-kDa binary toxin receptor (Cpm1/Cqm1), an alpha-glucosidase present in the larval midgut microvilli. In this work, we studied the molecular basis of the resistance developed by Culex quinquefasciatus to B. sphaericus C3-41. The cqm1 genes were cloned from susceptible (CqSL) and resistant (CqRL/C3-41) colonies, respectively. The sequence of the cDNA and genomic DNA derived from CqRL/C3-41 colony differed from that of CqSL one by a one-nucleotide deletion which resulted in a premature stop codon, leading to production of a truncated protein. Recombinant Cqm1S from the CqSL colony expressed in Escherichia coli specifically bound to the Bin toxin and had α-glucosidase activity, whereas the Cqm1R from the CqRL/C3-41 colony, with a deletion of three quarters of the receptor's C-terminal lost its α-glucosidase activity and could not bind to the binary toxin. Immunoblotting experiments showed that Cqm1 was undetectable in CqRL/C3-41 larvae, although the gene was correctly transcribed. Thus, the cqm1R represents a new allele in C. quinquefasciatus that confers resistance to B. sphaericus.
authors.affiliation: Key Laboratory of Agricultural and Environmental Microbiology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan 430071, China.
authors.forename: Qing-yun
authors.initials: QY
authors.lastname: Guo
authors.forename: Quan-xin
authors.initials: QX
authors.lastname: Cai
authors.forename: Jian-ping
authors.initials: JP
authors.lastname: Yan
authors.forename: Xiao-min
authors.initials: XM
authors.lastname: Hu
authors.forename: Da-sheng
authors.initials: DS
authors.lastname: Zheng
authors.forename: Zhi-ming
authors.initials: ZM
authors.lastname: Yuan
mesh_terms: D000818:Animals; D001407:Bacillus / Q000502:physiology; D001427:Bacterial Toxins; D003465:Culex / Q000382:microbiology / Q000502:physiology*; D005260:Female; D017344:Genes, Insect; D054884:Host-Pathogen Interactions; D007305:Insecticide Resistance / Q000235:genetics; D007814:Larva / Q000378:metabolism; D010572:Pest Control, Biological; D017422:Sequence Analysis, DNA; D017384:Sequence Deletion; D000520:alpha-Glucosidases / Q000235:genetics*
chemical_list: D001427:Bacterial Toxins; C046134:binB protein, Bacillus sphaericus; D000520:alpha-Glucosidases
keywords: Bacillus sphaericus; Culex quinquefasciatus; Resistance; Toxin binding; cqm1