Phylogenetic Characterization of the Energy-taxis Receptor Aer in Pseudomonas and Phenotypic Characterization in P. pseudoalcaligenes KF707

Chemotaxis allows bacteria to sense gradients in their environment and respond by directing their swimming. Aer is a receptor that, instead of responding to a specific chemoattractant, allows bacteria to sense cellular energy levels and move towards favourable environments. In Pseudomonas, the number of apparent Aer homologs differs between the only two species it had been characterized in, P. aeruginosa and P. putida. Here we combined bioinformatic approaches with deletional mutagenesis in P. pseudoalcaligenes KF707 to further characterize Aer. It was determined that the number of Aer homologs varies between 0-4 throughout the Pseudomonas genus, and they were phylogenetically classified into 5 subgroups. We also used sequence analysis to show that these homologous receptors differ in their HAMP signal transduction domains. Genetic analysis also indicated that some Aer homologs have likely been subject to horizontal transfer. P. pseudoalcaligenes KF707 was unique among species for having three Aer homologs as well as the receptors CttP and McpB. Phenotypic characterization in this species showed the most prevalent homolog of Aer was key, but not essential for energy-taxis. This study demonstrates that energy-taxis in Pseudomonas varies between species and provides a new naming convention and associated phylogenetic details for Aer chemoreceptors.