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

Abstract

14In coming decades drought is expected to expand globally owing to increased 15 evaporation and reduced rainfall. In order to reduce the vulnerability of agricultural 16 systems we need to understand the crop plant growth environment. Understanding, 17 predicting and controlling the rhizosphere has potential to harness plant microbe 18 interactions, improve plant responses to environmental stress and mitigate effects of 19 climate change. Our plant growth-promoting rhizobacteria (PGPR) are isolated from 20 the natural laboratory 'Evolution Canyon' Israel (EC). The endophytic rhizobacteria 21 from the wild progenitors of cereals have been co-habituated with their hosts for long 22 periods of time. The study revealed that silica particles (SN) triggered the PGPR 23 production of exopolysaccharides (EPS) containing D-glucuronate (D-GA). This leads 24 to increased plant biomass accumulation in drought-stressed growth environments. 25The PGPR increased EPS content increases the water holding capacity (WHC) and 26 osmotic pressure of the biofilm matrix. Light-and electron-microscopic studies show 27 that in the presence of SN particles, bacterial morphology is changed, indicating that 28 SNs are associated with significant reprogramming in bacteria. 29The results here show that the production of EPS containing D-GA is induced by SN 30 treatment. The findings encourage formulation of cells considering microencapsulation 31 with materials that ensure higher WHC and hyperosmolarity under field conditions. 32Our results illustrate the importance of considering natural soil nanoparticles in the 33 application of PGPR. Osmotic pressure involvement of holobiont cohabitation is 34 discussed. 35 36 65 keeper for the bacterial drought tolerance enhancement (Timmusk, Kim et al. 2015).66 EC is a well described natural laboratory where microbes have co-habituated with 67 the hosts over a long period of time (Nevo 2012). Reciprocity between the organisms 68 is generally accepted (Gilbert, Bosch et al. 2015, Gilbert 2016, Rice, Kallonen et al. 69 2016, Gilbert 2019) and organisms that have co-evolved within the environment are 70 more robust to environmental stress situations (Robinson, Klein et al. 2018, Vega 71 2019). Microbes found in extreme habitats developed a different strategy to adapt to 72 such conditions through evolution. Holobiotic complex relationships in the given 73 framework, not robotic associations of genes, are becoming more and more accepted 74 in developmental and evolutionary biology (Gilbert, Bosch et al. 2015, Gilbert 2016, 75 Rice, Kallonen et al. 2016, Gilbert 2019). Hence, understanding the framework of 76 adaptation to extreme environments is gaining interest in a period of environment 77 change (Robinson, Klein et al. 2018, Vega 2019) . 78 Our recent plant nanointerface interaction research focusing on native soil particles 79 shows that silica nanoparticles (SN) promote PGPR attachment and plant 80 colonization, and this effect is translated into crop yield enhancement under stress 81 condit...

The Effects of Plant-Associated Bacterial Exopolysaccharides on Plant Abiotic Stress Tolerance

“…The polysaccharides secreted by EPS-producing bacteria may be adsorbed on soil particles and cement them due to the formation of cation bridges, hydrogen bonding, van der Waals forces, and anion adsorption mechanisms between soil particles [ 130 , 131 , 132 ]. EPS has a highly cross-linked structure that enables it to shrink and swell yet remain saturated across a wide range of matric potentials [ 133 ].…”

“…For instance, xhantan and alginate polymers from Xhantomonas sp and Azotobacter vinelandii improve soil aggregate formation [ 134 ]. However, the formation of stable aggregates seems to depend on both the nature and the content of organic matter and the type of soil particles [ 131 , 132 , 135 , 136 ], and little is known about the rheological properties and thickening agents responsible for soil aggregates formation. One of the few studies that address this aspect of bacterial EPS suggests that the structure of the thickening agents of EPS produced by Rhizobium sp.…”

“…YAS34 are composed of glucose, galactose and mannuronic, and glucose, galactose, and glucuronic acid, respectively [ 136 ]. Interestingly, Fersiukh et al [ 132 ] have recently demonstrated that silica particles triggered the PGPR production of EPS containing D-glucuronate, which subsequently increases the water holding capacity and osmotic pressure of bacteria biofilm and root colonization, promoting plant growth in drought-stressed environments.…”

Realities and hopes in the application of microbial tools in agriculture

“…Many PGPMs treated with gold-, aluminium-and silver-coated nanoparticles have been reported to significantly increase plant growth and to inhibit pathogen growth (Gouda et al, 2018;Kumari and Singh, 2020). Recent studies have shown that the use of biocompatible titania and silica nanoparticles promoted the attachment and colonization of PGPMs, which resulted in plant biomass accumulation and growth improvements in stressful conditions (Timmusk et al, 2018;Fetsiukh et al, 2020). The development of nanoformulations containing Bt (or Bt-derived compounds) also holds great potential in increasing the shelf-life, efficacy and persistence in the field of these biopesticides (Devi et al, 2019).…”