0973-7510 Journal of Pure and Applied Microbiology 2581-690X DR. M.N. Khan 10.22207/JPAM.17.1.03 Toxicity Evaluation and Genetic Improvement of Bacillus thuringiensis Isolated from Different Regions in Assiut, Egypt against Mosquito Larvae Rafeek Abdallah Hesham Abd El-Latif Abd-Ella Aly A. Mahmoud Ghada Abd-Elmonsef Elfarash A.E. Department of Genetics, Faculty of Agriculture, Assiut University, 71526 Assiut, Egypt. Department of Genetics, Faculty of Agriculture, Beni-Suef University, Beni-Suef 62511, Egypt. Plant Protection Department, Faculty of Agriculture, Assiut University, 71526 Assiut, Egypt. Botany and Microbiology Department, Faculty of Science, Assiut University, P.O. 71516, Assiut, Egypt. 16 01 2023 17 1 143 154 Copyright © 2023 The Author(s) 2023 This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International License which permits unrestricted use, sharing, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.https://creativecommons.org/licenses/by/4.0/

This study aims to evaluate the toxicity and genetic improvement of Bacillus thuringiensis isolates. Isolates were obtained from soil, insect and water samples from different regions of Assiut, Egypt for biological control of mosquito larvae. B. thuringiensis colonies were identified based on morphological and then by PCR which detect the Cry toxic genes in the isolates. Bioassays were performed to evaluate the toxicity of different strains of B. thuringiensis against mosquito larvae such as (Culex spp). In general, 36 B. thuringiensis isolates were obtained (31 from soil, 4 from insects, and 1 from water). And they were all toxic to mosquito larvae with different mortality percentages from 7 to 97% after 48 hours. Isolate Am2 recorded the highest mortality percentage 97% and Mn3 lowest mortality percentage 7%. PCR revealed that Am2 isolate which caused the highest mortality encodes three different types of Cry toxins, Cyt1AA, Cry1Ac and Cry2Aa. This isolate Am2 was examined by scanning electron microscopy to observe the shape of the Cry proteins. The results showed that the Am2 isolate contained of spherical and cuboidal toxic proteins. Then UV-mutagenesis was performed on the Am2 isolate to improve its toxicity. Out of 30 obtained UV-mutants, only one mutant showed improvement in the mortality of mosquito larvae since it caused a mortality rate of 100%. The results of the present study revealed the larvicidal efficacy of B. thuringiensis (Am2) isolate found in the soil of Assiut, could be used in biological control program of mosquito larvae.

 Keywords B. thuringiensis Cry Genes Cyt Genes UV- mutagenesis Scanning Electron Microscope