List of primers used in this study.

<div><p><i>Burkholderia pseudomallei</i> is a facultative intracellular bacterial pathogen that causes melioidosis, a severe invasive disease of humans. We previously reported that the stress-related catecholamine hormone epinephrine enhances motility of <i>B</i>. <i>pseudomallei</i>, transcription of flagellar genes and the production of flagellin. It has been reported that the QseBC two-component sensory system regulates motility and virulence-associated genes in other Gram-negative bacteria in response to stress-related catecholamines, albeit disparities between studies exist. We constructed and whole-genome sequenced a mutant of <i>B</i>. <i>pseudomallei</i> with a deletion spanning the predicted <i>qseBC</i> homologues (<i>bpsl0806</i> and <i>bpsl0807</i>). The Δ<i>qseBC</i> mutant exhibited significantly reduced swimming and swarming motility and reduced transcription of <i>fliC</i>. It also exhibited a defect in biofilm formation and net intracellular survival in J774A.1 murine macrophage-like cells. While epinephrine enhanced bacterial motility and <i>fliC</i> transcription, no further reduction in these phenotypes was observed with the Δ<i>qseBC</i> mutant in the presence of epinephrine. Plasmid-mediated expression of <i>qseBC</i> suppressed bacterial growth, complicating attempts to <i>trans</i>-complement mutant phenotypes. Our data support a role for QseBC in motility, biofilm formation and net intracellular survival of <i>B</i>. <i>pseudomallei</i>, but indicate that it is not essential for epinephrine-induced motility <i>per se</i>.</p></div>