The Role of Trehalose-producing Bradyrhizobium japonicum and Azotobacter chroococcum in Enhancing Salinity Tolerance of Zea mays Plants

Abstract

Salinity is one of the most potent abiotic elements in nature and is damaging to both plants and microbes. Osmostress response in bacteria involves the accumulation of small organic compounds called compatible solutes as trehalose. In this work the synthesis and accumulation of trehalose by Bradyrhizobium japonicum strain (ARC 517) were investigated. Different sources of carbon, nitrogen, initial pH, and inoculum level were studied in order to increase trehalose productivity. An optimal production medium containing glucose and yeast extract was found suitable for trehalose production. The results showed that keeping the pH of the culture broth at 6.0 is important for trehalose production. Moreover the optimal level of inoculum was 4.0%. The optimized parameters gave a maximum trehalose production of 22.65 mg ml-1. Scanning electron microscope showed that cells of B. japonicum that enhanced for trehalose was aggregated and became the longest with length about 3 times higher than that of control. The results of field experiment revealed that, the Zea mays plants treated with B. japonicum strain (ARC 517) that enhanced for trehalose + Azotobacter chroococcum retained higher relative water content (RWC), chlorophyll content, K+/Na+ ratio as compared to other treatments. Positive correlation between trehalose overproduction and high-yield parameters were observed under saline conditions. These findings suggest that trehalose overproduction could be a beneficial characteristic for biofertilizers.