Plant-Associated Bacteria and the Rhizosphere

Plants interact with diverse soil microorganisms providing niches for growth, and in particular, plant roots represent hot spots for multitrophic interactions. This chapter presents the obtained knowledge on the belowground microbial compartments of the plant microbiome, elucidating the differences between the rhizosphere, the rhizoplane, and the endosphere. On the basis of plant-driven microbial colonization, plant-associated bacteria can be divided into free-living soil bacteria, rhizosphere colonizers, rhizoplane colonizers, and endophytes. Root colonization by bacteria most likely starts with the adhesion of cells to the root surface, in which process exopolysaccharides synthesized by bacteria play an important role. Roots growing through soil induce physicochemical changes in the surrounding soil, thus providing a different environment as compared to non-vegetated soil. Bacteria that cause plant damage through infection or production of phytotoxic compounds are called pathogenic bacteria. Plant—microbe interactions are complex and the outcome can be positive, negative, or neutral.