Role of Chemotaxis Toward Fusaric Acid in Colonization of Hyphae of Fusarium oxysporum f. sp. radicis-lycopersici by Pseudomonas fluorescens WCS365

Abstract

Pseudomonas fluorescens WCS365 is an excellent competitive colonizer of tomato root tips after bacterization of seed or seedlings. The strain controls tomato foot and root rot (TFRR) caused by the phytopathogenic fungus Fusarium oxysporum f. sp. radicis-lycopersici. Under biocontrol conditions, fungal hyphae were shown to be colonized by WCS365 bacteria. Because chemotaxis is required for root colonization by WCS365 cells, we studied whether chemotaxis also is required for hyphae colonization. To that end, an in vitro assay was developed to study hyphae colonization by bacteria. The results indicated that cells of the cheA mutant FAJ2060 colonize hyphae less efficiently than cells of wild-type strain WCS365, when single strains were analyzed as well as when both strains were applied together. Cells of WCS365 show a chemotactic response toward the spent growth medium of F. oxysporum f. sp. radicis-lycopersici, but those of its cheA mutant, FAJ2060, did not. Fusaric acid, a secondary metabolite secreted by Fusarium strains, appeared to be an excellent chemo-attractant. Supernatant fluids of a number of Fusarium strains secreting different levels of fusaric acid were tested as chemo-attractants. A positive correlation was found between chemo-attractant activity and fusaric acid level. No chemotactic response was observed toward the low fusaric acid-producer FO242. Nevertheless, the hyphae of FO242 still were colonized by WCS365, suggesting that other metabolites also play a role in this process. The possible function of hyphae colonization for the bacterium is discussed.

Transcriptome profiling of bacterial responses to root exudates identifies genes involved in microbe-plant interactions

“…1). Again, this finding could reflect differences in levels of key attractants in the two exudates that could conceivably play a role in host selection because chemotaxis plays an important role in successful colonization of the rhizosphere (21,(24)(25)(26)(27)(28). Some genes encoding proteins with functions previously implicated in microbial-plant interactions were down-regulated in response to both root exudates (Fig.…”

Bacterial-Fungal Interactions: Hyphens between Agricultural, Clinical, Environmental, and Food Microbiologists

“…Chemotaxis (directed movement) of bacteria toward fungi and fungally derived molecules has been demonstrated in several instances; for example, both detrimental and beneficial Pseudomonas species exhibit taxis toward fungal mycelial exudates (93,139). In the case of the chemotactic response of the biocontrol strain Pseudomonas fluorescens WCS365, Fusarium oxysporum fusaric acid has been identified as an important fungally derived chemotactic signal (95). Cellcell contact between fungi and bacteria can result in important changes to their physiology and interactions.…”

Dual transcriptional profiling of a bacterial/fungal confrontation: Collimonas fungivorans versus Aspergillus niger

“…For example, Pseudomonas fluorescens is chemoattracted to fusaric acid produced by Fusarium oxysporum f. sp. radicis lycopersici (Forl) (de Weert et al, 2004). Of particular interest to us is oxalate, given the upregulation of Collimonas genes involved in the utilization of this compound.…”