Submitted to: Book Chapter
Publication Type: Book / chapter
Publication Acceptance Date: 1/10/2006
Publication Date: 6/1/2006
Citation: Bacon, C.W., Hinton, D.M. 2006. Bacterial endophytes: the endophytic niche, its occupants, and its utility. In: Gnanamanickam, S.S., editor. Plant-Associated Bacteria. Dordrecht, The Netherlands: Springer. p. 155-194. Interpretive Summary: Bacteria that dwell within plants as nonpathogens and contribute to the health and defense of the plant against diseases are considered as beneficial bacteria. These bacteria are being exploited as biological control agents in plants against several major plant diseases. The bacteria are located between plant cells within the plant and are referred to as bacterial endophytes. The specific location of the bacteria is called the apoplasm. In this chapter we review the structure, chemical composition and variations of the apoplasm, and review work to show that contrary to prior opinion, the apoplasm is not nutrient poor but rich in several classes of bacterial nutrients. Also we develop theories on how bacteria that live within this nutrient rich location might be modified to compete with other organisms that also invade the apoplasm. Finally, we present useful strategies on the uses of bacterial endophytes for purposes other than biocontrol, and how plants targeted as hosts for bacteria endophytes should be genetically developed for larger and more consistent apoplasm suitable for increased colonization of bacterial endophytes.
Technical Abstract: The endophytic niche offers a unique habitat for the control of pathogens since the endophyte is contained and is not subject to the direct influence of the environment and will multiply within the intercellular spaces as the plant grows, thereby potentially colonizing the entire plant axis. The bacterium is protected, contained within a relatively stable environment, and in our preliminary trials with one endophytic species, there were no genetic modifications of this strain during and after a season’s growth. However, the use of multiple endophytic strains of the same species, or genus within the same plant might result in altered genetic properties. The association is long-term, as the effects from an endophyte can still be detected after two or more years. The major uses of endophytic bacteria are reviewed and these include: To control plant diseases; to enhance plant growth responses via the production of growth hormones; to serve as transformation agents of plants with useful value added products that can be expressed in planta; to serve as agents of environmental decontaminations in the area of remediating polluted soils.