Microbial‐iron interactions in the plant rhizosphere. An overview

Abstract

From a microbiologist's viewpoint, iron is an important key regulatory element which can exert a significant influence on microbial‐plant interactions occurring in the rhizosphere. Microorganisms can create substantial changes in the soil solution bathing the roots of plants. Examples of this ability are cited in this brief overview, using data gathered on the production of siderophores, high‐affinity Fe(III) chelating molecules, from bacteria and other microorganisms. The biological diversity of these systems is noted in molecular structure and genetic studies. Similarly, plant stress responses due to iron limitation are known, which include changes in root exudation, a major source of substrates for microbial growth. In vitro, in vivo, and field observations support the critical nature of the iron requirement of both plants and microorganisms. Initial attempts to manipulate or introduce microbial flora for biocontrol purposes have lead to the importance of understanding microbial colonization of this niche. The application of recombinant genetics offers the opportunity to develop and test new means of experimentation and manipulations in the rhizosphere. As an example, the introduction of foreign genes into fluorescent pseudomonads for tracking and monitoring purposes is presented as an aid to colonization studies.

Key words:

• iron
• siderophore
• root colonization
• biocontrol
• gene regulation
• lac genes
• HCN