Authors: REDA GAAFAR, WEDAD KASIM, RANIA ABOU-ALI, MOHAMED OMAR, HEBA HEWAIT
Abstract: Gamma rays are known to induce random mutations, which are used to enhance the production of biofilms in bacteria. Therefore, to improve the activity of biofilm formation in wild Bacillus amyloliquefaciens (HM6), this bacterial strain was mutated using five doses of gamma irradiation. Sixteen mutants and their wild strain B. amyloliquefaciens (HM6) were tested for biofilm formation under two different (250 and 350 mM) NaCl concentrations. Only six mutants exhibited a significant increase in biofilm formation under 350 mM NaCl. Inoculation of salt-stressed Giza123 barley seedlings with the two mutants (M1 and M7), which showed distinguishable rep-PCR patterns, and their wild strain significantly decreased MDA content. In addition, such inoculation inhibited POX and CAT activities, while AsA content was increased. The lowest POX and CAT activities, as well as the highest AsA content, were recorded with mutant M7. The full length cDNA of Giza123 APX1 was cloned, sequenced, and submitted to GenBank under accession number MF804856. In BLASTX analysis, its sequence exhibited 99% homology with the Hordeum vulgare peroxisome type ascorbate peroxidase. RT-PCR revealed variable APX1 expression levels in the stressed and nonstressed Giza123 seedlings. Salt stress upregulated the APX1 expression level in uninoculated?stressed seedlings compared to the uninoculated?unstressed ones. On the other hand, inoculation with M1 and M7 mutants and their wild strain modified the APX1 expression level, where the wild and the M1 mutant downregulated the APX1 expression level, while mutant M7 upregulated its expression level under salt stress.
Keywords: Biofilm, Bacillus amyloliquefaciens , salt stress, APX1 expression, Gamma irradiation
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