ABSTRACT

ABSTRACT Siderophore is an iron-healing compound that has an immense role in microbial interaction, especially in the rhizosphere. Siderophore is present in one of the major mechanisms of bacteria that is involved in the biological control of plant diseases. Both plant pathogenic fungi and bacteria are reported to be inhibited by siderophore-producing biocontrol agents. These siderophores are produced in iron-limited conditions to sequester the

8.1 Iron Importance .................................................................................................................... 168 8.2 Siderophore ........................................................................................................................... 168

8.2.1 Siderophores: Structures and Binding Sites ............................................................. 169 8.2.2 Hydroxymate Siderophore ........................................................................................ 169 8.2.3 Catecholate Siderophores ......................................................................................... 170 8.2.4 Carboxylate (Complexion) Siderophore .................................................................... 170 8.2.5 Mixed Siderophores .................................................................................................. 170 8.2.6 Pyoverdin .................................................................................................................. 170 8.2.7 Siderophore Biosynthesis .......................................................................................... 171 8.2.8 Mechanism of Siderophore Export ........................................................................... 171 8.2.9 Transport of Iron-Siderophore Complex .................................................................. 172 8.2.10 Metabolism of Iron ................................................................................................... 173 8.2.11 Iron Regulation in Bacteria ...................................................................................... 173

8.3 Applications of Siderophore ................................................................................................. 174 8.4 Mechanisms of Siderophore in Biocontrol: Overview ......................................................... 175 8.5 Phytopathology ..................................................................................................................... 176 8.6 Bacteria-Pathogen Interactions ............................................................................................ 177

8.6.1 Bacterial Soft Rot of Potato ...................................................................................... 177 8.6.2 Tomato Bacterial Wilt ............................................................................................... 177 8.6.3 Rice Bacterial Blight ................................................................................................ 178 8.6.4 Bacterial Canker of Tomato ...................................................................................... 179 8.6.5 Bacterial Blight of Cotton ......................................................................................... 179 8.6.6 Bacterial Leaf Spot of Mungbean............................................................................. 180 8.6.7 Fire Blight Disease ................................................................................................... 180

8.7 Conclusion ............................................................................................................................ 181 Acknowledgments .......................................................................................................................... 181 References ...................................................................................................................................... 181

less-available iron from the environment and thereby deprive the pathogen of iron, which ultimately leads to inhibition. Three main groups of siderophores have been reported: hydroxymate siderophore, catecholate siderophore, and mixed siderophore. Siderophores are synthesized through two different biosynthetic pathways: NRPSs-dependent and non-NRPSsdependent. The ABC-type transporter proteins are also involved in the delivery of iron-siderophore complex into the cytosol of the producing organism, where it can be utilized. Some pathogenic bacteria capable of producing siderophores are highly virulent. Siderophore interacts with the H2O2 and peroxidases in the affected tissue either to enhance oxidative stress induced by harpin, coded by an hrpN gene, or to protect bacterial cells by inhibiting the generation of  reactive oxygen species. In this chapter we discuss control of bacterial plant pathogens with  the production of siderophore by antagonistic rhizobacterium. Emphasis is given to the most economically important bacterial plant diseases such as bacterial soft rot of potato, tomato bacterial wilt, bacterial canker of tomato, rice bacterial blight, bacterial blight of cotton, bacterial leaf spot of mungbean, and re blight disease in apple. An overview is included of the signicance of siderophores in the context of the inhibition of plant pathogenic bacteria.