Rhizosphere Bacterial Signalling: A Love Parade Beneath Our Feet

Abstract

Plant roots support the growth and activities of a wide variety of microorganisms that may have a profound effect on the growth and/or health of plants. Among these microorganisms, a high diversity of bacteria have been identified and categorized as deleterious, beneficial, or neutral with respect to the plant. The beneficial bacteria, termed plant growth-promoting rhizobacteria (PGPR), are widely studied by microbiologists and agronomists because of their potential in plant production. Azospirillum, a genus of versatile PGPR, is able to enhance the plant growth and yield of a wide range of economically important crops in different soils and climatic regions. Plant beneficial effects of Azospirillum have mainly been attributed to the production of phytohormones, nitrate reduction, and nitrogen fixation, which have been subject of extensive research throughout the years. These elaborate studies made Azospirillum one of the best-characterized genera of PGPR. However, the genetic and molecular determinants involved in the initial interaction between Azospirillum and plant roots are not yet fully understood. This review will mainly highlight the current knowledge on Azospirillum plant root interactions, in the context of preceding and ongoing research on the association between plants and plant growth-promoting rhizobacteria.

Keywords :

• Plant Growth-Promoting Bacteria
• Azospirillum
• Colonization

ACKNOWLEDGMENTS

The authors acknowledge financial support from Norsk Hydro and scientific advice from P. Goddard. The authors like to thank R. De Mot, C. Michiels, Y. Okon, and P. Cornelis for their valuable contributions during discussions while writing this review.

In honor of the 100th anniversary of Prof. Lorenz Hiltner's introduction of the Rhizosphere concept in 1904.