Motility behavior of Azospirillum species in response to aromatic compounds

The motility of Azospirillum lipoferum Sp59b and Azospirillum brasilense Sp7 in the presence of the aromatic compounds benzoate, protocatechuate, 4-hydroxybenzoic acid, and catechol was studied using computer-assisted video motion analysis. Increases in swimming speed with concomitant decreases in the rate of change in direction and increases in path linearity are indicative of bacterial chemoattraction. With the exception of 4-hydroxybenzoic acid, the aromatic compounds tested altered the motility patterns of both species, consistent with a chemoattraction mechanism. 4-Hydroxybenzoic acid elicited significant behavioral changes only in A. brasilense. The highest speeds were recorded for most compounds at concentrations between 1 and 10 mM for A. lipoferum and at lower concentrations for A. brasilense. Catechol, supplied at a 10 mM concentration, reduced the swimming speed of A. brasilense but not of A. lipoferum. The distinct differences in swimming behavior observed between these two species of Azospirillum in response to aromatic compounds may be of ecological significance in soils.Key words: Azospirillum spp., motility, video motion analysis, aromatic compounds.