Metal tolerance and larvicidal activity of Lysinibacillus sphaericus

Lysinibacillus sphaericus is a spore-forming bacterium used in the biological control of mosquitoes and in bioremediation. Mosquito larvae exposed to heavy metals are tolerant to concentrations above the permissible limit for industrial residual waters. In this work, we characterize 51 L. sphaericus strains for metal tolerance and larvicidal activity against Culex quinquefasciatus. Lysinibacillus sphaericus OT4b.2, OT4b.20, OT4b.25, OT4b.26 and OT4b.58 were as toxic as the spores of the reference strain 2362 against C. quinquefasciatus larvae. 19 Mosquito-pathogenic L. sphaericus strains and 6 non-pathogenic strains were able to grow in arsenate, hexavalent chromium and/or lead. 16S rRNA gene sequences and phylogenetic analyses clustered 84 % of the metal-tolerant strains in L. sphaericus group 1, which encompasses the mosquitocidal strains. The larvicidal activity of vegetative and sporulated cells and its high tolerance to arsenate, hexavalent chromium and lead indicate that L. sphaericus OT4b.26 is a strong candidate for further studies examining its potential for biological control of mosquitoes in waters contaminated with metals.