Screening and identification of extracellular polysaccharide-producing strain and the influence on soil quality and crop growth

Abstract:

[Background] Some microorganisms, with high production of extracellular polysaccharide, can help improve saline-alkali soil and promote crop growth. [Objective] To screen saline-alkali-tolerant and extracellular polysaccharide-producing microorganisms for the development of microbial agents which can improve saline-alkali soil. [Methods] We screened strains which reproduce in saline-alkali soil, produce extracellular polysaccharide, and have the ability to solubilize phosphate and release potassium from rhizosphere soil of plants in coastal saline-alkali area. The eligible strain was identified based on morphological observation, physiological and biochemical indexes, 16S rRNA gene and gyrB gene sequencing. Then we analyzed growth of the strain and the production of extracellular polysaccharide under saline-alkali stress. In addition, the influence of the strain on the proportion of aggregates with different particle sizes in saline-alkali soil was investigated, and the effect on growth indexes of tomato in saline-alkali soil and soil indexes was examined. [Results] From 727 strains in coastal saline-alkali soil, strain GBW HF-98 was screened out, which, with strong reproductive ability in saline-alkali soil, produced extracellular polysaccharide and had the ability to solubilize phosphate and release potassium. The strain was identified as Bacillus subtilis subsp. inaquosorum and it can tolerate pH 10.0 stress and NaCl concentration of up to 110 g/L. It significantly improved the proportion of aggregates with different particle sizes in soil with mild and moderate salinity. The high dose of this strain (T2 group) increased the strong seedling index, root dry weight, dry weight of whole plant, stem diameter, and plant height of tomato in soil with moderate salinity by 33.8%, 59.3%, 37.2%, 12.3%, and 15.6%, respectively, as compared with the control (P<0.05). Moreover, it significantly reduced pH, total salt content, and soil bulk density by 8.9%, 27.9%, and 17.9%, respectively, and significantly raised soil available phosphorus content and available potassium content by 36.0% and 17.4%, separately (P<0.05).[Conclusion] GBW HF-98, with high production of extracellular polysaccharide, can remarkably promote the growth of tomato in moderately saline-alkali soil and improve the soil. Thus, it can be used for the development of microbial agents for the improvement of saline-alkali soil.