Structural, compositional characterization of novel exopolysaccharide from halotolerant strain of Pseudomonas entomophila PE3 and their role in growth promotion of sunflower under saline condition

Abstract

Pseudomonas entomophila PE3, a plant growth promoting bacterium, was characterized for exopolysaccharides (EPS) production under different saline conditions. EPS production was optimized using Box-Behnken Design and response surface methodology (RSM). Carbohydrate, protein and phenolic contents of EPS were maximum at 2 % and minimum at 8 % NaCl concentration. Gas chromatography-mass spectrometry (GC-MS) analysis showed that EPS was composed of unusual trisaccharide melezitose and non-carbohydrate moieties included proteins, esters, carboxylic acid and composition changed on exposure to salinity. X-ray diffraction (XRD) analysis showed amorphous nature of EPS interrupted with salt crystals. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were conducted to report changes in morphology and elemental composition of EPS under saline and non-saline conditions. 1H NMR spectroscopy showed peaks of melezitose (α-D glucose and β-D fructose) in EPS at all salt concentrations. Additional sugars (α-D glucose and α-D galactose) were reported in EPS extracted at 2 % NaCl. The exhibition of salt-tolerance traits by EPS further confirmed the polymer as ‘stress molecule’. The study also reported that upon application of EPS and PE3, salt-stressed sunflower plants showed significant improvement in growth and productivity under pot conditions. The novel bioformulation also instigated salt-tolerance traits in treated plants and improved their survival under unhospitable conditions, thereby promoting the concept of sustainable agriculture.