Isolation, identification and evaluation of mosquito entomopathogenic Bacillus species and related genera from randomly selected sites in Kenya

Abstract

This study was carried out to identify specific mosquitocidal Bacillus species and related genera for future development of biopesticides in local mosquito control program in Kenya. Bacterial isolation was conducted from 100 soil samples through pasteurization method and preliminary identification conducted through phenotypical analysis. Toxicity analysis was performed through bioassays and lethal concentrations (LC) were determined using probit analysis. Toxic isolates were further identified through analysis of the 16s rRNA and screening of toxin genes through PCR. Expression of toxin proteins was performed using SDS-PAGE. Out of 453 isolates, 7 of them were found to yield highly potent toxicity (>50% mortality) against Culex quinquefasciatus during the initial toxicity assays. Among them, two isolates KDHa3 and SKDHb5, with LC50 values of 0.007mg/L and 0.008mg/L, respectively, were the most toxic against the target. Phylogenetic analysis based on 16s rRNA showed high homology to Lysinibacillus sphaericus (six isolates) and Bacillus thuringiensis (one isolate). Various toxin genes encoding BinA, BinB, Mtx (1, 2 and 3), Cry48A, Cry49A, Cry4A, Cry11A and Cyt1A were detected among the isolates. The protein profiles using SDS-PAGE were consistent with the standard strains Lysinibacillus sphaericus C3-41 and B. thuringiensis var. israelensis. Native toxic Bacillus species and related genera were identified with this study being the first to report highly toxic strains of L. sphaericus and B. thuringiensis strains from Kenyan soil samples.

Mosquitoes of Etiological Concern in Kenya and Possible Control Strategies

“…Nevertheless, the prices of these imported products have been a limiting factor especially for large-scale applications. In recent work by Karungu et al [142], larvicidal strains of B. thuringiensis and L. sphaericus were successfully isolated from Kenyan soil samples. These local strains can be used to produce a local Kenyan based bio-larvicide using cheap home-based agricultural products as raw materials for solid-state fermentation (SSF) and submerged fermentation (SmF).…”

Endophytic Bacillus Bacteria Living in Sugarcane Plant Tissues and Telchin licus licus Larvae (Drury) (Lepidoptera: Castniidae): The Symbiosis That May Open New Paths in the Biological Control

“…The entomopathogenic potential of these strains was not tested although it is already known that B. thuringiensis have the ability to control larvae of D. saccharalis (Gitahy et al, 2007), S. frugiperda (Monnerat et al, 2003), P. xylostella (Monnerat et al, 2009), A. gossypii (Melatti et al, 2010), and the species Brevibacillus laterosporus have been shown to be toxic to the diamondback moth (Ormskirk et al, 2019). Another species that has been observed with activity against Culex quinquefasciatus is Lysinibacillus sphaericus (Karungu et al, 2018). These studies suggest that different species or bacterial genera have the potential for biological control application.…”