Utilization of drought-tolerant bacterial strains isolated from harsh soils as a plant growth-promoting rhizobacteria (PGPR)

Noha M Ashry; Bothaina A Alaidaroos; Shereen A Mohamed; Omnia A M Badr; Mohamed T El-Saadony; Ahmed Esmael

doi:10.1016/j.sjbs.2021.10.054

Utilization of drought-tolerant bacterial strains isolated from harsh soils as a plant growth-promoting rhizobacteria (PGPR)

Saudi J Biol Sci. 2022 Mar;29(3):1760-1769. doi: 10.1016/j.sjbs.2021.10.054. Epub 2021 Oct 25.

Authors

Noha M Ashry¹, Bothaina A Alaidaroos², Shereen A Mohamed³, Omnia A M Badr³, Mohamed T El-Saadony⁴, Ahmed Esmael⁵

Affiliations

¹ Agriculture Microbiology Department, Faculty of Agriculture, Benha University, Qalubia 13736, Egypt.
² Department of Biological Sciences, Faculty of Sciences, King Abdulaziz University, Saudi Arabia.
³ Department of Genetics and Genetic Engineering, Faculty of Agriculture, Benha University, Qalubiya Governorate 13736, Egypt.
⁴ Department of Agricultural Microbiology, Faculty of Agriculture, Zagazig University, 44511 Zagazig, Egypt.
⁵ Botany and Microbiology Department, Faculty of Science, Benha University, Qalubiya Governorate, 13511, Egypt.

Abstract

Drought stress adversely affects plant health and productivity. Recently, drought-resistant bacterial isolates are used to combat drought resistance in crops. In this in vitro study, 20 bacterial isolates were isolated from harsh soil; their drought tolerance was evaluated using four concentrations of polyethylene glycol (PEG) 6000. The two most efficient isolates (DS4 and DS9) were selected and identified using 16S rRNA genetic sequencing. They were registered in the NCBI database and deposited under accession numbers MW916285 and MW916307 for Bacillus cereus (DS4) and Bacillus albus (DS9), respectively. These isolates were screened for plant growth-promoting properties compared to non-stressed conditions. Biochemical parameters; Proline, salicylic acid, gibberellic acid (GA), indole acetic acid (IAA), antioxidant activity, and antioxidant enzymes were measured under the same conditions, and in vitro seed germination was tested under stress conditions and inoculation with selected isolates. The results showed that under the harsh conditions of PEG6000, DS4 produced the highest amount of IAA of 1.61 µg/ml, followed by DS9 with 0.9 µg/ml. The highest amount of GA (49.95 µg/ml) was produced by DS9. On the other hand, the highest amount of siderophore was produced from DS4 isolate followed by DS9. Additionally, DS4 isolate recorded the highest exopolysaccharide (EPS) content of 3.4 mg/ml under PEG (-1.2 MPa) followed by DS9. The antioxidant activity increased in PEG concentrations depending manner, and the activity of the antioxidant enzymes increased, as catalase (CAT) recorded the highest activity in DS4 with an amount of 1.095 mg/ml. additionally, an increase in biofilm formation was observed under drought conditions. The isolated mixture protected the plant from the harmful effects of drought and showed an increase in the measured variables. Under unstressed conditions, the highest rates of emulsification index (EI 24%) were obtained for DS4 and DS9, at 14.92 and 11.54, respectively, and decreased under stress. The highest values of germination, total seedling length, and vigor index were obtained upon inoculation with the combination of two strains, and were 100%, 4.10 cm, and 410, respectively. Therefore, two strains combination is an effective vaccine capable of developing and improving drought tolerance in dryland plants.

Keywords: 16s rRNA; Antioxidant activity; Antioxidant enzymes; Drought tolerance; PGPR.