Energy taxis is the dominant behavior in Azospirillum brasilense

Energy taxis encompasses aerotaxis, phototaxis, redox taxis, taxis to alter native electron accepters, and chemotaxis to oxidizable substrates. The sig nal for this type of behavior is originated within the electron transport s ystem. Energy taxis was demonstrated, as a part of an overall behavior, in several microbial species, but it did not appear as the dominant determinan t in any of them. In this study, we show that most behavioral responses pro ceed through this mechanism in the alpha-proteobacterium Azospirillum brasi lense. First, chemotaxis to most chemoeffectors typical of the azospirilla habitat was found to be metabolism dependent and required a functional elec tron transport system. Second, other energy-related responses, such as aero taxis, redox taxis, and taxis to alternative electron accepters, were found in A. brasilense. Finally, a mutant lacking a cytochrome c oxidase of the cbb(3) type was affected in chemotaxis, redox taxis, and aerotaxis. Altoget her, the results indicate that behavioral responses to most stimuli in A. b rasilense are triggered by changes in the electron transport system.