Rhizobacteria

Cross section though a soybean (Glycine max 'Essex') root nodule: The rhizobacteria, Bradyrhizobium japonicum, colonizes the roots and establishes a nitrogen-fixing symbiosis. This high-magnification image shows part of a cell with single bacteroids within their host plant. In this image, endoplasmic reticulum, dictysome, and cell wall can be seen.

Rhizobacteria are root-associated bacteria that can have a detrimental (parasitic varieties), neutral or beneficial effect on plant growth. The name comes from the Greek rhiza, meaning root. The term usually refers to bacteria that form symbiotic relationships with many plants (mutualism). Rhizobacteria are often referred to as plant growth-promoting rhizobacteria, or PGPRs. The term PGPRs was first used by Joseph W. Kloepper in the late 1970s and has become commonly used in scientific literature.[1]

Generally, about 2–5% of rhizosphere bacteria are PGPR.[2] They are an important group of microorganisms used in biofertilizer. Biofertilization accounts for about 65% of the nitrogen supply to crops worldwide.[citation needed] PGPRs have different relationships with different species of host plants. The two major classes of relationships are rhizospheric and endophytic. Rhizospheric relationships consist of the PGPRs that colonize the surface of the root, or superficial intercellular spaces of the host plant, often forming root nodules. The dominant species found in the rhizosphere is a microbe from the genus Azospirillum.[3][failed verification] Endophytic relationships involve the PGPRs residing and growing within the host plant in the apoplastic space.[1]

  1. ^ a b Vessy, J. Kevin (August 2003). "Plant Growth Promoting Rhizobacteria as Biofertilizers". Plant and Soil. 255 (2): 571–586. doi:10.1023/A:1026037216893. ISSN 0032-079X. S2CID 37031212.
  2. ^ Antoun H, Prevost D (2005). Ecology of plant growth promoting rhizobacteria. In: Siddiqui ZA (Eds.) PGPR: Biocontrol and Biofertilization, Springer, The Netherlands, pp. 2
  3. ^ Bloemberg, Guido V.; Lugtenberg, Ben J. J. (August 2001). "Molecular basis of plant growth promotion and biocontrol by rhizobacteria". Current Opinion in Plant Biology. 4 (4): 343–350. doi:10.1016/S1369-5266(00)0183-7. PMID 11418345.