Silica particles trigger the production of exopolysaccharides in harsh environment plant growth-promoting rhizobacteria and increase their ability to enhance drought tolerance

ABSTRACT In coming decades drought is expected to expand globally owing to increased evaporation and reduced rainfall. In order to reduce the vulnerability of agricultural systems we need to understand the crop plant growth environment. Understanding, predicting and controlling the rhizosphere has potential to harness plant microbe interactions, improve plant responses to environmental stress and mitigate effects of climate change. Our plant growth-promoting rhizobacteria (PGPR) are isolated from the natural laboratory ‘Evolution Canyon’ Israel (EC). The endophytic rhizobacteria from the wild progenitors of cereals have been co-habituated with their hosts for long periods of time. The study revealed that silica particles (SN) triggered the PGPR production of exopolysaccharides (EPS) containing D-glucuronate (D-GA). This leads to increased plant biomass accumulation in drought-stressed growth environments. The PGPR increased EPS content increases the water holding capacity (WHC) and osmotic pressure of the biofilm matrix. Light- and electron-microscopic studies show that in the presence of SN particles, bacterial morphology is changed, indicating that SNs are associated with significant reprogramming in bacteria. The results here show that the production of EPS containing D-GA is induced by SN treatment. The findings encourage formulation of cells considering microencapsulation with materials that ensure higher WHC and hyperosmolarity under field conditions. Our results illustrate the importance of considering natural soil nanoparticles in the application of PGPR. Osmotic pressure involvement of holobiont cohabitation is discussed.