Isolation, characterization and evaluation of mosquitocidal activity of <i>Lysinibacillus</i> strains obtained from <i>Culex pipiens</i> larvae

Abstract

Three strains—C107, C207, and C307—of spore-forming Gram-positive motile rod-shaped bacteria were isolated from dead larvae of <i>Culex pipiens</i> in La Plata city, Argentina. The three bacterial strains have different phenotypic and molecular characteristics. A comparative analysis of their 16S rRNA gene sequences and phylogenetic analysis demonstrated that isolates C107 and C207 were related to reference strains of <i>Lysinibacillus sphaericus</i>, while C307 was related to <i>Bacillus licheniformis</i>. The cytomorphology, biochemical characterization, and phylogenetic relatedness corroborated these respective group assignments. The isolated bacterial strain exhibited the same PCR amplified pattern for the <i>binA</i>, <i>binB</i>, and <i>mtx</i> genes as did the reference strains used. These bacterial strains presented different pathogenic actions among the following mosquito species tested: <i>Culex pipiens</i>, <i>Aedes aegypti</i>, <i>Culex dolosus</i>, <i>Culex apicinus</i>, <i>Ochlerotatus albifasciatus</i>, and <i>Anopheles albitarsis</i>. Only isolates C107 and C207 exhibited mosquitocidal activity. <i>Culex pipiens</i> was the species most susceptible to C107 (LC₅₀, 4 × 10⁴ spores/ml), while <i>O. albifasciatus</i> was most susceptible to C207 (LC₅₀, 3.4 × 10⁶ spores/ml).