Oxygen‐dependent regulation of c‐di‐GMP synthesis by SadC controls alginate production in Pseudomonas aeruginosa

Abstract

Pseudomonas aeruginosa produces increased levels of alginate in response to oxygen-deprived conditions. The regulatory pathway(s) that links oxygen limitation to increased synthesis of alginate has remained elusive. In the present study, using immunofluorescence microscopy, we show that anaerobiosis-induced alginate production by planktonic PAO1 requires the diguanylate cyclase (DGC) SadC, previously identified as a regulator of surface-associated lifestyles. Furthermore, we found that the gene products of PA4330 and PA4331, located in a predicted operon with sadC, have a major impact on alginate production: deletion of PA4330 (odaA, for oxygen-dependent alginate synthesis activator) caused an alginate production defect under anaerobic conditions, whereas a PA4331 (odaI, for oxygen-dependent alginate synthesis inhibitor) deletion mutant produced alginate also in the presence of oxygen, which would normally inhibit alginate synthesis. Based on their sequence, OdaA and OdaI have predicted hydratase and dioxygenase reductase activities, respectively. Enzymatic assays using purified protein showed that unlike OdaA, which did not significantly affect DGC activity of SadC, OdaI inhibited c-di-GMP production by SadC. Our data indicate that SadC, OdaA and OdaI are components of a novel response pathway of P. aeruginosa that regulates alginate synthesis in an oxygen-dependent manner.

The SiaA/B/C/D signaling network regulates biofilm formation in Pseudomonas aeruginosa

“…Additionally, direct interaction of SiaC with SiaD regulates the DGC activity of the latter, consistent with the observation in vivo that siaC is required for the SiaD‐mediated promotion of biofilm formation (Fig D). In P. aeruginosa , the DGC WspR is activated by phosphorylation and the activity of SadC is controlled by its transmembrane domain and the presence of oxygen (Hickman et al , ; Schmidt et al , ; Zhu et al , 2016a). Post‐translational modulation of the activity of SiaD by its direct interaction with SiaC is in agreement with these reports.…”

Pseudomonas aeruginosa Alginate Overproduction Promotes Coexistence with Staphylococcus aureus in a Model of Cystic Fibrosis Respiratory Infection

“…Indeed, a recent report demonstrated alginate can interfere with PQS signaling—a feature limited to alginate producers; no such inhibition of signaling was observed for the non-alginate-producing neighbors (53). Alginate has also been shown to restrict the diffusion of oxygen (54–56) and aminoglycoside antibiotics (57), and to bind and sequester reactive intermediates and iron (58). These properties may explain how alginate is able to reduce the production of multiple P. aeruginosa virulence factors.…”

Functional Characterization of c-di-GMP Signaling-Related Genes in the Probiotic Lactobacillus acidophilus

“…Many DGCs and PDEs contain responsive regulator (REC) domains that can receive input signals for responding to environmental stimulation. A well-characterized P. aeruginosa strain contains several DGCs and PDEs that regulate cellular c-di-GMP levels and sense input signals, such as chemoattractants (WspR) and oxygen-deprived conditions (SadC), to alter intracellular c-di-GMP levels (O'Connor et al, 2012; Schmidt et al, 2016). For Gram-negative bacteria, the transmembrane GGDEF protein is generally located on the inner membrane and can form components of the response pathway with sensory proteins located in the periplasm or outer membrane (Kim and Harshey, 2016; Schmidt et al, 2016).…”