Chemotaxis in Azospirillum

Abstract

The ability of Azospirillum to colonize the roots of plants depends on motility and chemotaxis. Azospirillum cells are motile and capable of chemotaxis toward organic acids, sugars, and some aminoacids. Azospirillum is also able to navigate gradients of oxygen, alternative electron acceptors, and redox active compounds. Most attractants and repellents described thus far for this bacterial genus include compounds that affect intracellular metabolism, leading to the suggestion that most taxis responses correspond to energy taxis in Azospirillum spp. Several spatial and temporal gradient assays that can be implemented as quantitative methods are available to characterize taxis responses in Azospirillum species. The analysis of complete sequence genomes of several Azospirillum species reveals that taxis responses are coordinated by multiple chemotaxis pathways. All genomes also possess a chemotaxis pathway that is predicted to regulate alternative cellular functions other than flagellar motility. Genome analyses indicate that all Azospirillum spp. sequenced to date encode for an extremely large repertoire of putative chemotaxis receptors, which is likely contributing to explaining their ubiquitous distribution.