Post‐transcriptional regulation of the virulence‐associated enzyme A lg C by the σ 22 ‐dependent small RNA E rs A of P seudomonas aeruginosa

Summary The small RNA E rs A of P seudomonas aeruginosa , transcribed from the same genomic context of the well‐known E scherichia coli   S pot 42, has been characterized. We show that, different from S pot 42, E rs A is under the transcriptional control of the envelope stress response, which is known to impact the pathogenesis of P . aeruginosa through the activity of the alternative sigma factor σ 22 . The transcriptional responsiveness of E rs A RNA also spans infection‐relevant cues that P . aeruginosa can experience in mammalian hosts, such as limited iron availability, temperature shifts from environmental to body temperature and reduced oxygen conditions. Another difference between S pot 42 and E rs A is that E rs A does not seem to be involved in the regulation of carbon source catabolism. Instead, our results suggest that E rs A is linked to anabolic functions for the synthesis of exoproducts from sugar precursors. We show that E rs A directly operates in the negative post‐transcriptional regulation of the alg C gene that encodes the virulence‐associated enzyme A lg C , which provides sugar precursors for the synthesis of several P . aeruginosa polysaccharides. Like E rs A , the activation of alg C expression is also dependent on σ 22 . Altogether, our results suggest that E rs A and σ 22 combine in an incoherent feed‐forward loop to fine‐tune A lg C enzyme expression.