Molecular analysis of Culex quinquefasciatus larvae responses to Lysinibacillus sphaericus Bin toxin

Abstract

Lysinibacillus sphaericus produces the mosquito larvicidal binary toxin consisting of BinA and BinB, which are both required for toxicity against Culex and Anopheles larvae. The molecular mechanisms behind Bin toxin-induced damage remain unexplored. We used whole-genome microarray-based transcriptome analysis to better understand how Culex larvae respond to Bin toxin treatment at the molecular level. Our analyses of Culex quinquefasciatus larvae transcriptome changes at 6, 12, and 18 h after Bin toxin treatment revealed a wide range of transcript signatures, including genes linked to the cytoskeleton, metabolism, immunity, and cellular stress, with a greater number of down-regulated genes than up-regulated genes. Bin toxin appears to mainly repress the expression of genes involved in metabolism, the mitochondrial electron transport chain, and the protein transporter of the outer/inner mitochondrial membrane. The induced genes encode proteins linked to mitochondrial-mediated apoptosis and cellular detoxification including autophagic processes and lysosomal compartments. This study is, to our knowledge, the first microarray analysis of Bin toxin-induced transcriptional responses in Culex larvae, providing a basis for an in-depth understanding of the molecular nature of Bin toxin-induced damage.

A differential transcriptional profile by Culex quinquefasciatus larvae resistant to Lysinibacillus sphaericus IAB59 highlights genes and pathways associated with the resistance phenotype

“…The intrinsic apoptotic pathway is specifically activated in response to mitochondria damage, resulting in the cytochrome C release from these organelles and caspases activation that leads to other events, including DNA degradation [72]. A higher expression of caspase 3 in susceptible larvae treated with Bin toxin was an effect caused by this toxin to the cells [73]. The action of Bin toxin induces autophagy in the midgut cells and subsequent cytoplasmic vacuolization as it has been well documented in larvae subjected to Bin treatment [16, 17].…”

Bacterial Toxins Active against Mosquitoes: Mode of Action and Resistance

“…A transcriptome analysis comparing untreated and Bin-treated Cx. p. quinquefasciatus larvae revealed differential expression of transcripts involved in mitochondria mediated apoptosis and autophagy responses [ 174 ]. Another study comparing susceptible and Bin-resistant larvae revealed an outstanding differential expression of transcripts involved in apoptosis and DNA metabolism [ 175 ].…”

Culex quinquefasciatus Resistant to the Binary Toxin from Lysinibacillus sphaericus Displays a Consistent Downregulation of Pantetheinase Transcripts

“…An association between toxicity to insects with growth has been reported, for instance, for spinosad, a biological larvicide based on metabolites of the bacterium Saccharopolyspora spinosa that acts as a neurotoxin [44] which has been recently investigated for its potential effects as an insect growth regulator [45,46]. DEGs possibly related to the toxin mode of action could also be those encoding for regulators of DNA damage, as evidence for the involvement of apoptosis in the mode of action of Bin and Cry toxins has been shown [47][48][49]. Indeed, the transcriptome of the RIAB59 resistant larvae also pointed out several DEGs related to apoptosis and DNA maintenance [26].…”