Motility and chemotactic response of Pseudomonas fluorescens toward chemoattractants present in the exudate of Macrophomina phaseolina

Pseudomonas fluorescens strains (LAM1-hydrophilic) and (LAM2-hydrophobic) s howed positive chemotaxis towards attractants (su-ars, amino acids, polyols and organic acids) present in the exudate of Macrophomina phaseolina (a so ilborne plant pathogenic fungus). The varied response of motility traits su ch as speed, rate of change in direction (RCDI) and net to gross displaceme nt ratio (NGDR) was observed for different chemoattractants. Swimming speed of the strains was highest in 10-fold diluted exudate or 100-1000 muM stre ngth of different attractants, but further dilutions significantly decrease d the swimming speed (P = 0.05). Chemotactic response of P. fluorescens was positively correlated with swimming speed (P = 0.05; r = 0.76). Relative t o control, the RCDI values decreased 1.5-fold in amino acids or sugars, and 1.2-fold in polyols or organic acids. With increase in swimming speed, the NGDR of both strains also increased, but the RCDI decreased. Both hydrophi lic and hydrophobic strains did not show significant differences in their m otility traits. The results demonstrate that M. phaseolina exudate contains chemical attractants that serve as signal for flagellar motility of P fluo rescens. Motile P. fluorescens strains thus may consume fungal exudate as n utrients, and thus spores could offer a niche for these bacteria in soil.