Bacillus velezensis Wall Teichoic Acids Are Required for Biofilm Formation and Root Colonization

Abstract

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 Bacillus strains is essential for the use of these strains in agriculture. Here, we observed that an sfp gene mutant of the plant growth-promoting rhizobacterium Bacillus velezensis 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 Δsfp mutant, and impairment of the ggaA 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 ΔgtaB 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 Bacillus strain, which will help improve its application as a biofertilizer. IMPORTANCE Bacillus velezensis is a Gram-positive plant-beneficial bacterium which is widely used in agriculture. Additionally, Bacillus 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 Bacillus strains remain largely unknown. Here, we showed that WTAs play important roles in the plant root colonization process. The loss of the gtaB gene affects the ability of B. velezensis 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 Bacillus root colonization process and can help improve our understanding of plant-rhizobacterium interactions.

Plant growth-promoting activities and genomic analysis of the stress-resistant Bacillus megaterium STB1, a bacterium of agricultural and biotechnological interest

“…In fact, two clusters containing polysaccharide biosynthesis genes were found ( Table S11 ). In addition, several genes involved in the production of teichoic acids, which play a role in biofilm formation and root colonization [59] were also identified ( Table S3 ).…”

Effects of Calcium and Signal Sensing Systems on Azorhizobium caulinodans Biofilm Formation and Host Colonization

“…For many bacteria, such as Bacillus amyloliquefaciens, Enterococcus faecalis, and Vibrio fischeri, the successful colonization of a host is influenced by their ability to attach and form a biofilm (Yaryura et al, 2008;Tischler et al, 2018;Xu et al, 2018;Willett et al, 2019). For P. syringae pv.…”

“…A. caulinodans cannot only fix atmospheric nitrogen with S. rostrata in a symbiotic state ( Dreyfus and Dommergues, 1981 ), but also can fix nitrogen in a free-living state ( Dreyfus et al, 1983 ) or in association with non-legume plants, such as rice and wheat ( Liu et al, 2017a ). During the establishment of rhizobia-plant associations, biofilm formation on plant surfaces plays an important role ( Yaryura et al, 2008 ; Xu et al, 2018 ). However, the process of biofilm formation of A. caulinodans and the role of biofilm formation on its early symbiosis with S. rostrata are less studied.…”

The Interactions of Rhizodeposits with Plant Growth-Promoting Rhizobacteria in the Rhizosphere: A Review

“…to poor colonizer P. fluorescens strain WCS307 increased colonization of root tips [45]. Another study conducted by Xu et al [46] reported that wall teichoic acid (WTA) in B. velezensis SQR9 is crucial for root colonization and biofilm formation.…”