Role of Phenazine-1-Carboxamide Produced by Pseudomonas chlororaphis PCL1391 in the Control of Tomato Foot and Root Rot
Tomato foot and root rot (TFRR) is a tomato root disease caused by the fungus Fusarium oxysporum f. sp. radicis-lycopersici (Forl). No chemicals are available which efficiently suppress TFRR. In this chapter we show that the bacterium Pseudomonas chlorora
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Role of Phenazine-1-Carboxamide Produced by Pseudomonas chlororaphis PCL1391 in the Control of Tomato Foot and Root Rot Ben Lugtenberg and Geneviève Girard Abstract Tomato foot and root rot (TFRR) is a tomato root disease caused by the fungus Fusarium oxysporum f. sp. radicis-lycopersici (Forl). No chemicals are available which efficiently suppress TFRR. In this chapter we show that the bacterium Pseudomonas chlororaphis strain PCL1391 is able to suppress the disease. To this end it uses antibiosis as its (major) disease-suppressing mechanism. The produced antibiotic was identified as phenazine-1-carboxamide (PCN). In contrast to the PCN-producing bacterium, pseudomonads which produce the PCN biosynthetic precursor phenazine-1-carboxylic acid (PCA) as their major phenazine were not active in disease suppression. However, when PCA was converted to PCN by complementing these strains with the phzH gene, which encodes an amidotransferase, the complemented strains produced PCN and controled TFRR. In order to be effective in disease control, strain PCL1391 should be able to produce PCN under a variety of environmental conditions. We therefore studied the regulation of PCN production under various environmental factors, by regulatory genes, by the plant, and by the pathogenic fungus. Special attention was paid to the secondary metabolite fusaric acid secreted by the fungus. Fusaric acid is detected by the bacterium as a chemo-attractant to reach the fungus, to colonize its surface and to finally use it as a food source. Conversely, fusaric acid is used by the fungus to inhibit the production of PCN and to reduce the bacterial growth rate. It is clear that during disease control the PCN-producing bacterium wins this battle. The result of the evaluation of the described studies is that we can understand in quite some detail how P. chlororaphis strain PCL1391 acts as a disease control agent and also why it is not active under all environmental conditions.
B. Lugtenberg (&) G. Girard Institute of Biology, Leiden University, Sylvius Laboratory, Sylviusweg 72 2333 BE, Leiden, The Netherlands e-mail: [email protected]
S. Chincholkar and L. Thomashow (eds.), Microbial Phenazines, DOI: 10.1007/978-3-642-40573-0_8, Springer-Verlag Berlin Heidelberg 2013
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Abbreviations CAS CLSM C6-HSL Forl gfp PCA PCN TFRR
Casamino acids Confocal laser scanning microscopy N-hexanoyl-L-homoserine lactone Fusarium oxysporum f. sp. radicis-lycopersici Gene encoding green fluorescent protein Phenazine-1-carboxylic acid Phenazine-1-carboxamide Tomato foot and root rot
8.1 Introduction Tomato foot and root rot (TFRR) is a root disease caused by the fungus Fusarium oxysporum f. sp. radicis-lycopersici (Forl). TFRR is also called crown and root rot of tomato. TFRR is a serious problem for field and greenhouse crops (Jarvis 1988). Chemicals do not efficiently suppress TFRR (Benhamou et al. 1994). In contrast, some bacteria are fortunately able to reduce TFRR (Haas and Défago 2005; Lugtenberg and Kamilova
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