Identification of mosquito larvicidal bacterial strains isolated from north Sinai in Egypt

Abstract

In the present study, two of the most toxic bacterial strains of Bacillus sphaericus against mosquito were identified with the most recent genetic techniques. The PCR product profiles indicated the presence of genes encoding Bin A, Bin B and Mtx1 in all analyzed strains; they are consistent with protein profiles. The preliminary bioinformatics analysis of the binary toxin genes sequence revealed that the open reading frames had high similarities when matched with nucleotides sequence in the database of other B. sphaericus strains. The biological activity of B. sphaericus strains varied according to growing medium, and cultivation time. The highest yield of viable counts, spores and larvicidal protein were attained after 5 days. Poly (P) medium achieved the highest yield of growth, sporulation, protein and larvicidal activity for all tested strains compared to the other tested media. The larvicidal protein produced by local strains (B. sphaericus EMCC 1931 and EMCC 1932) in P medium was more lethal against the 3rd instar larvae of Culex pipiens than that of reference strains (B. sphaericus 1593 and B. sphaericus 2297). The obtained results revealed that P medium was the most effective medium and will be used in future work in order to optimize large scale production of biocide by the locally isolated Bacillus sphaericus strains.

Optimization of Bio-Mosquitocidal Production using Local Bacterial Strains of Bacillus Sphaericus

“…The variation in the composition of the tested media in their contents of carbon and nitrogen sources as well as minerals found to affect wholly both yield and toxicity of biocide [12]. Although, B. sphaericus is considered an undemanding bacterial species, neither requiring differential or selective culture media, nor it depends on special conditions to develop.…”

“…Two actively marked toxic strains of Bacillus sphaericus EMCC 1931 and B. sphaericus EMCC 1932, previously isolated from the soil of north Sinai in Egypt [12], were used in the present study along with the reference strains of B. sphaericus 1593 and 2297 as highly toxic strains [2]. The reference strains, B. sphaericus1593 and B. sphaericus 2297, were kindly provided by Prof. Dr. Y.…”

“…The ratio of carbon to nitrogen was determined as 3.5:1.0 and calculated to give final concentrations of carbon and nitrogen as 8.43 and 2.40 g/l [12]. In addition, the effect of inorganic mineral salts was also studied.…”

“…Series of experiments were carried out using the poly medium [14] that showed the best productivity [12] to optimize fermentation conditions for maximum growth, sporulation, toxic proteins synthesis and their activity against 3 rd instar Culex pipiens larvae.…”

“…Most of studies cited aimed to obtain microbial growth and toxic protein yield similar to or higher than that attained by reference laboratory medium, in such comparative studies researchers always used one random reference medium [6][7][8][9][10][11]. In our previous study [12], we evaluated five conventional laboratory media named: poly medium, nutrient yeast extract salt, glucose-glutamatesalts-EDTA, Luria Bertani and acetate yeast extract medium, for the growth and biocide production by B. sphaericus strains EMCC1931, EMCC1932 along with the reference strains. The results proved that medium composition has a great effect on the growth, sporulation and biocide production.…”