Gamma irradiation enhancement of biofilm production in  Bacillus amyloliquifaciens and effect of mutants’ inoculation on  APX1  expression in salt-stressed Egyptian barley

Rania ABOU-ALI,Heba HEWAIT,Mohamed OMAR,Wedad KASIM,Reda GAAFAR

doi:10.3906/bot-1711-29

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.

Highlights

Crop plants frequently undergo different adverse environmental conditions of which soil salinity represents the most serious abiotic stress threatening agriculture worldwide (Witzel et al, 2014)
The results showed that the biofilm formation activity of mutants was significantly increased in sixteen mutants (M1, M2, M6, M7, M15, M16, M20, M25, M28, M34, M36, M37, M40, M41, M42, and M44), while the other mutants did not show any significant change in their activity for biofilm formation when compared to the wild strain (Figure 1A)
The results showed that under salt stress, B. amyloliquefaciens mutants exhibited variable activity for biofilm formation and the most significant increase in the activity of biofilm formation was observed in 6 mutants (M1, M2, M7, M28, M34, and M40), where their absorbance values were 0.275, 0.283, 0.258, 0.238, 0.375, and 0.233, respectively, under 350 mM NaCl compared to the wild strain (0.165) (Figure 1B)

Summary

Introduction

Crop plants frequently undergo different adverse environmental conditions of which soil salinity represents the most serious abiotic stress threatening agriculture worldwide (Witzel et al, 2014). Plant growth promoting rhizobacteria (PGPR) were applied to alleviate salt stress, as well as to maintain a reasonable level of productivity under high salt concentrations (Singh et al, 2011; Nadeem et al, 2012). Barley (Hordeum vulgare L.) is one of the most cultivated crops worldwide Among cereals, it is the most salt-tolerant crop. There are few studies that have investigated the growth promotion of barley using PGPR (Omar et al, 2009; Chang et al, 2014; Nabti et al, 2015). This is probably due to its inherent salt tolerance compared to other crops such as corn, soybean, wheat, tomato, and rice

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Conclusion