Environmental Distribution, Frequency and Toxicity of Bacillus thuringiensis in Syria

Abstract

Aims: Bacillus thuringiensis is distinguished by its production of proteinaceous parasporal inclusion bodies during sporulation, which when ingested by susceptible insects, are activated in the midgut into toxins. B. thuringiensis can be isolated from numerous sources; however, there has been no recorded isolation of B. thuringiensis strains from Syria. Therefore, this study aimed at investigating the distribution, frequency and toxicity of B. thuringiensis isolated from different ecosystems in Syria. Study Design: This study describes the first isolation of the entomopathogenic bacterium, Bacillus thuringiensis in Syria. Place and Duration of Study: Scientific Agriculture Research Center in Lattakia, Syria, 2011-2012. Methodology: B. thuringiensis was isolated from soil samples collected from twenty different ecosystem-sites. The characterization of B. thuringiensis isolates was performed using morphological examination of colony morphology and formation of parasporal inclusion bodies. The crystal morphology of B. thuringiensis was observed by scanning electron microscopy. A bioassay was done to test the efficacy of B. thuringiensis against Galleria mellonella. Results: Forest, beach and cultivated soils had more B. thuringiensis strains than uncultivated and interior arid soils. The frequency of B. thuringiensis was partially dependant on organic matter and pH content of the soil. A total of 65% of the isolates was found to be toxic to G. mellonella. The most toxic isolate of B. thuringiensis was obtained from cultivated area and produced bipyramidal, cuboidal and rectangular inclusions. Conclusion: The comparison of the distribution of B. thuringiensis in different ecosystems might lead to a better understanding of the ecology of this organism. It is widespread in diverse environments including beaches and uncultivated soils. The presence of organic matter increases the population of B. thuringiensisin soils, suggesting that the bacteria have parasitic and saprophytic properties that let them to multiply both inside and outside insects' bodies.