Abstract
Most habitats host diverse bacterial communities, offering opportunities for inter-species interactions. While competition might often dominate such interactions, little is known about whether bacteria can sense competitors and mount adequate responses. The competition sensing hypothesis proposes that bacteria can use cues such as nutrient stress and cell damage to prepare for battle. Here, we tested this hypothesis by measuring transcriptome changes in Pseudomonas aeruginosa exposed to the supernatant of its competitor Burkholderia cenocepacia. We found that P. aeruginosa exhibited significant growth-medium-dependent transcriptome changes in response to competition. In an iron-rich medium, P. aeruginosa upregulated genes encoding the type-VI secretion system and the siderophore pyoverdine, whereas genes encoding phenazine toxins and hydrogen cyanide were upregulated under iron-limited conditions. Moreover, general stress response and quorum sensing regulators were upregulated upon supernatant exposure. Altogether, our results reveal nuanced competitive responses of P. aeruginosa when confronted with B. cenocepacia supernatant, integrating both environmental and social cues.