Bacillus sphaericus is an aerobic, endospore-forming gram-positive bacterium having toxicity against different mosquito species. The B. sphaericus strain toxic to mosquito larvae was first reported by

Kellen et al. (1965), Pexidartinib manufacturer and thereafter, more than 300 strains have been isolated and identified from all over the world (de Barjac et al., 1988; Sun et al., 1996). Highly toxic strains produce a parasporal crystal, whereas others with less toxicity lack a parasporal crystal. Bacillus sphaericus produces two types of toxins, mosquitocidal toxins (Mtx) and binary toxins (Bin), which are toxic to mosquito larvae (Broadwell & Baumann, 1987; Thanabalu et al., 1991). These toxins differ in composition and time of synthesis. The Mtx toxins appear to be synthesized in low-toxicity strains (Nielsen-LeRoux & Charles, 1992), as well as in some of the highly selleck chemicals llc toxic strains, and are expressed during the vegetative phase of growth. The Bin toxins are the main toxic factors responsible for killing mosquito larvae. They contain two polypeptides, receptor binding BinB (51.4 kDa) and toxic BinA (41.9 kDa), which act as a binary toxin (Charles et al., 1997). After ingestion by susceptible larvae, Bin toxins dissolve in the alkaline midgut and are activated by gut proteases. The 41.9 kDa BinA protein is converted to 39 kDa,

and 51.4 kDa BinB is converted to 43 kDa (Baumann et al., 1991). The activated BinB binds to the receptor present on the larval midgut (Silva-Filha et al., 1999), while activated BinA induces

the toxicity by interacting with BinB (Oei et al., 1992). The exact mechanism of the mode of action of Bin toxins is not clearly understood, partly due to the fact that the three-dimensional structure of the two toxins or the binary toxin has not been revealed. Although both these toxins are required in equimolar concentrations for maximal toxicity (Baumann et al., 1991), BinA alone has also been shown to be mildly toxic to the Culex larvae (Charles et al., 1997; Hire et al., 2009). The mosquitocidal activity of B. sphaericus has mainly been attributed to the presence of Bin and Mtx proteins. Several strains of B. sphaericus PAK6 have been found to exist in nature, which differ in the toxicity profile towards mosquito larvae. It is therefore important to have a systematic approach to isolate potent strains of this bacterium to exploit them as an effective biocontrol agent for mosquito control. In this paper, we report the mosquitocidal activity of three indigenous B. sphaericus strains. Interestingly, the ISPC-8 strain displays superior mosquitocidal properties as compared with the standard strains, 1593 and 2362. The superior toxicity and activity spectrum of ISPC-8 was further characterized by purification and characterization of its binary proteins. Three indigenous strains, ISPC-5, ISPC-6 and ISPC-8, of B. sphaericus were isolated in our laboratory. ISPC-5 (Menon et al.