Ulva prolifera polysaccharide enhances the root colonisation by Bacillus amyloliquefaciens strain Cas02

The application of biocontrol agent is important for the sustainable development of agriculture. Unsuccessful or limited colonisation by plant growth-promoting rhizobacteria (PGPR) has become an important constraint factor for their commercial application. Here, we report that Ulva prolifera polysaccharide (UPP) promotes root colonisation by Bacillus amyloliquefaciens strain Cas02. UPP serves as an environmental signal for bacterial biofilm formation and its glucose residue is used as a carbon source for the synthesis of the exopolysaccharides and poly-gamma-glutamate present in biofilm matrix. Greenhouse experiments demonstrated that UPP could effectively enhance the root colonisation by Cas02 in both the bacterial population and survival time under natural semiarid soil conditions. Furthermore, the microbiome analysis also indicated the promoted colonisation by Cas02, as well as the improved bacterial rhizosphere community structure, after combined treatment of UPP and Cas02. This study provides a practical approach to improve the biocontrol agent with seaweed polysaccharides.