RNAseq reveals that Pseudomonas aeruginosa mounts medium-dependent competitive responses when sensing diffusible cues from Burkholderia cenocepacia
Most habitats on earth are colonized by diverse bacterial communities, offering ample opportunities for inter-species interactions. While competition for space and nutrients might often dominate such interactions, little is known about whether bacteria can sense competitors and mount specific responses to withstand their attacks. The competition-sensing hypothesis proposes that bacteria can do so through nutrient stress and cell damage cues. Here, we conducted a replicated RNAseq-transcriptomic study to test this hypothesis. We exposed Pseudomonas aeruginosa to either its own spent medium or to the supernatant of its competitor Burkholderia cenocepacia. Compared to controls, we detected significant changes in the transcriptome of P. aeruginosa that entail both general responses to spent medium and specific responses to the competitor. Specifically, genes encoding various competitive traits, including the type-VI secretion system, the siderophore pyoverdine, and the toxins phenazines and hydrogen cyanide, were upregulated when exposed to the competitor supernatant. Similarly, several stress response and quorum-sensing regulators were overexpressed. Moreover, we found transcriptional responses to vary as a function of iron availability, whereby metabolically more costly responses were launched under iron rich conditions. Altogether, our results reveal nuanced competitive responses of P. aeruginosa when exposed to B. cenocepacia supernatant, integrating both environmental and social cues. Overall design: Using Illumina High Seq to analyze P.a. gene expression when grown in supernatant of B.c. under high and low iron availabilty. As comparisons P.a. was grown in its own supernatant and in fresh medium only under the same iron treatments. Experiments were performed in triplicates.