Wall Teichoic Acids Are Required for Biofilm Formation and Root Colonization.

Rhizosphere colonization by plant growth-promoting rhizobacteria (PGPR) along plant roots facilitates the ability of PGPR to promote plant growth and health. Thus, an understanding of the molecular mechanisms of the root colonization process by plant-beneficial strains is essential for the use of these strains in agriculture. Here, we observed that an gene mutant of the plant growth-promoting rhizobacterium SQR9 was unable to form normal biofilm architecture, and differential protein expression was observed by proteomic analysis. A minor wall teichoic acid (WTA) biosynthetic protein, GgaA, was decreased over 4-fold in the Δ mutant, and impairment of the gene postponed biofilm formation and decreased cucumber root colonization capabilities. In addition, we provide evidence that the major WTA biosynthetic enzyme GtaB is involved in both biofilm formation and root colonization. The deficiency in biofilm formation of the Δ mutant may be due to an absence of UDP-glucose, which is necessary for the synthesis of biofilm matrix exopolysaccharides (EPS). These observations provide insights into the root colonization process by a plant-beneficial strain, which will help improve its application as a biofertilizer. is a Gram-positive plant-beneficial bacterium which is widely used in agriculture. Additionally, spp. are some of the model organisms used in the study of biofilms, and as such, the molecular networks and regulation systems of biofilm formation are well characterized. However, the molecular processes involved in root colonization by plant-beneficial strains remain largely unknown. Here, we showed that WTAs play important roles in the plant root colonization process. The loss of the gene affects the ability of SQR9 to sense plant polysaccharides, which are important environmental cues that trigger biofilm formation and colonization in the rhizosphere. This knowledge provides new insights into the root colonization process and can help improve our understanding of plant-rhizobacterium interactions.