Post-transcriptional regulation of the virulence-associated enzyme AlgC by the σ22 (AlgU/T)-dependent small RNA SPA0122 of Pseudomonas aeruginosa

Pseudomonas aeruginosa is the major cause of chronic and often fatal lung infections in cystic fibrosis individuals and of numerous acute infections in immune-compromised patients. It produces a large assortment of virulence factors and is endowed with an exquisite capability to form biofilm and to develop resistance to multiple classes of antibiotics. Expression of these traits is fine-tuned by a dynamic and intricate regulatory network [1]. In bacterial pathogens, small RNAs (sRNAs) have been recognized as key elements of the regulatory networks for the coordinate expression of the virulence factors underlying the interaction with host [2]. This study focused on the novel P. aeruginosa sRNA SPA0122 [3] expressed from the intergenic region amid the conserved genes polA and engB like the well-characterized Escherichia coli sRNA Spot 42. Our results indicate that the transcription of SPA0122 is strictly dependent on the envelope stress-responsive sigma factor σ22 (AlgT/U), the functional homolog of E. coli σE. Connected to the belonging to σ22 regulon, we show that SPA0122 is responsive to envelope stress, being induced by the cell wall-inhibitory antibiotic D-cycloserine. In addition, its transcriptional responsiveness spans infection-relevant cues that P. aeruginosa can experience in mammalian hosts, like limited iron availability, temperature shifts from environmental to body temperature and reduced oxygen conditions. Finally, we show that SPA0122 directly operates a negative post-transcriptional regulation of the algC gene, encoding the enzyme that provides sugar precursors for the synthesis of P. aeruginosa polysaccharides alginate, Psl and Pel, as well as LPS and rhamnolipids. Like SPA0122, activation of algC expression is also dependent on σ22. Altogether, our results suggest that SPA0122 and σ22 combine to bring about an incoherent feed-forward loop for the fine tuning of AlgC enzyme expression. 1. Balasubramanian et al. (2013) A dynamic and intricate regulatory network determines Pseudomonas aeruginosa virulence. Nucleic Acids Res, 41:1-20. 2. Caldelari et al. (2013) RNA-mediated regulation in pathogenic bacteria. Cold Spring Harb Perspect Med 2013;3:a010298. 3. Ferrara et al. (2012) Comparative profiling of Pseudomonas aeruginosa strains reveals differential expression of novel unique and conserved small RNAs. PLoS One, 7:e36553.