Isolation and characterization of native Bacillus thuringiensis strains from Saudi Arabia with enhanced larvicidal toxicity against the mosquito vector Anopheles gambiae (s.l.).

BACKGROUND: Worldwide, mosquito vectors are transmitting several etiological agents of important human diseases, including malaria, causing millions of deaths every year. In Saudi Arabia, as elsewhere, vector-control is based mostly on chemical insecticides which may be toxic and cause environmental deprivation. Here, to support the development of bio-pesticide alternatives, a study was conducted to identify native Bacillus thuringiensis (Bt) isolates with improved toxicity against the malaria vector, Anopheles gambiae (s.l.). METHODS: Sixty-eight Bt isolates were obtained from 300 soil and other samples collected from 16 sites across Saudi Arabia. Bt identification was based on morphological characteristics of colonies, shape of parasporal crystals and biochemical profiles. After characterization of their mosquitocidal activity, larvicidal strains were described through 16S ribosomal DNA gene sequencing, cry, cyt and chi genes PCR-amplification profiles, and SDS-PAGE protein analyses. RESULTS: Spherical Bt crystals were predominant amongst the 68 isolates (34%), while irregular, bi-pyramidal and spore-attached crystals were found in 32, 13 and 21% of strains, respectively. LC50 and LC90 bioassays showed that 23/68 isolates were larvicidal, with distinct biochemical activity profiles compared to non-larvicidal Bt strains. Eight larvicidal strains showed larvicidal activity up to 3.4-fold higher (LC50 range: 3.90-7.40 µg/ml) than the reference Bti-H14 strain (LC50 = 13.33 µg/ml). Of these, 6 strains had cry and cyt gene profiles similar to Bti-H14 (cry4Aa, cry4Ba, cry10, cry11, cyt1Aa, cyt1Ab, cyt2Aa). The seventh strain (Bt63) displaying the highest larvicidal activity (LC50 = 3.90 µg/ml) missed the cry4Aa and cyt1Ab genes and had SDS-PAGE protein profiles and spore/crystal sizes distinct from Bti-H14. The eight strain (Bt55) with LC50 of 4.11µg/ml had cry and cyt gene profiles similar to Bti-H14 but gave a chi gene PCR product size of 2027bp. No strains harbouring cry2, cry17 + 27, cry24 + 40, cry25, cry29, cry30, or cyt2Ba were detected. CONCLUSION: This study represents the first report of several Saudi indigenous Bt strains with significantly higher larvicidal efficacy against An. gambiae than the reference Bti-H14 strain. The very high toxicity of the Bt63 strain, combined with distinct cry and cyt genes and SDS-PAGE-protein profiles makes it a promising candidate for future applications in mosquito bio-control.

Amino acids content and electrophoretic profile of camel milk casein from different camel breeds in Saudi Arabia.

This study aimed to evaluate amino acids content and the electrophoretic profile of camel milk casein from different camel breeds. Milk from three different camel breeds (Majaheim, Wadah and Safrah) as well as cow milk were used in this study. Results showed that ash and moisture contents were significantly higher in camel milk casein of all breeds compared to that of cow milk. On the other hand, casein protein of cow milk was significantly higher compared to that of all camel milk breeds. Molecular weights of casein patterns of camel milk breeds were higher compared to that of cow milk. Essential (Phe, Lys and His) and non-essential amino acids content was significantly higher in cow milk casein compared to the casein of all camel milk breeds. However, there was no significant difference for the other essential amino acids between cow casein and the casein of Safrah breed and their quantities in cow and Safrah casein were significantly higher compared to the other two breeds. Non-essential amino acids except Arg and the essential amino acids (Met, Ile, Lue and Phe) were also significantly higher in cow milk α-casein compared to α-casein from all camel breeds. Moreover, essential amino acids (Val, Phe and His) and the non-essential amino acids (Gly and Ser) content was significantly higher in cow milk ß-casein compared to the ß-casein of all camel milk breeds and the opposite was true for Lys, Thr, Met and Ile. However, Met, Ile, Phe and His were significantly higher for ß-casein of Majaheim compared to the other two milk breeds. The non-essential amino acids (Gly, Tyr, Ala and Asp) and the essential amino acids (Thr, Val and Ile) were significantly higher in cow milk κ-casein compared to that for all camel milk breeds. There was no significant difference among all camel milk breeds in their κ-casein content of most essential amino acids. Relative migration of casein bands of camel milk casein was not identical. The relative migration of αs-, ß- and κ-casein of camel casein was slower than those of cow casein. The molecular weights of αs-, ß- and κ-casein of camel caseins were 27.6, 23.8 and 22.4 KDa, respectively. More studies are needed to elucidate the structure of camel milk.