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Bacillus velezensis strain S3-1 has a broad range of hosts and is used as a biocontrol agent and biofertilizer. However, the interaction of maize root exudates and colonization of the strain S3-1 has not yet been investigated. In our study, strain S3-1 effectively colonized both rhizosphere soil and root tissue. Collected maize root exudates significantly induced the chemotaxis, cluster movement, and biofilm formation of strain S3-1, showing increases of 1.43, 1.6, and 2.08 times, respectively, compared with the control. In addition, the components of root exudates (organic acids: citric acid, malic acid, and oxalic acid; amino acids: glycine, proline and phenylalanine; sugars: glucose, fructose, and sucrose) were tested. Each of these compounds could induce chemotactic response, swarming motility, and biofilm formation significantly. The strongest chemotactic response and swarming motility were found when malic acid was applied, but maximal ability of biofilm formation was stimulated by proline. Furthermore, we found that these compounds of root exudates stimulated the population of S3-1 adhering to the maize root surface, especially in the presence of malic acid. These results indicate that maize root exudates play an important role in the colonization of S3-1, and provide a deeper understanding of the interaction between plants and microorganisms. [ABSTRACT FROM AUTHOR]

Plasmid mobilization is important for environments. However, the effects of rhizospheres and root exudates on plasmid mobilization have received little attention. To address this problem, mobilization of the pSUP106 plasmid by a TOL-like plasmid from Pseudomonas fluorescens P13 into rifampicin-resistant P13 cells was investigated by biparental and triparental matings in the rhizosphere soils of maize seedlings and bulk soils. Mobilization frequencies were higher in the rhizosphere than in bulk soils. Plasmid mobilization frequencies decreased with vertical and horizontal distance away from plant roots. Furthermore, plasmid mobilization frequencies increased with growing contents of root exudates and artificial root exudate (ARE) of maize seedlings for 1 or 5 d of incubation time; however, donor and recipient population remained basically stable for all contents. Individual components of the exudates failed to promote mobilization of pSUP106 but a combination of sugars and amino acids of the exudates did. Removal of individual components from the ARE reduced the plasmid mobilization-promoting activity but simultaneous removal of several components destroyed the plasmid mobilization. All the data suggest that the rhizosphere of maize seedlings promoted the mobilization of the pSUP106 plasmid by the TOL-like plasmid and that root exudate of maize seedlings was the important driver of plasmid mobilization. The individual components of root exudates were necessary to increase plasmid mobilization but their combination was important for plasmid mobilization. [ABSTRACT FROM AUTHOR]