The anti-sigma factor MucA is required for viability inPseudomonas aeruginosa

Abstract

Pseudomonas aeruginosa causes chronic lung infections in people with cystic fibrosis (CF), and this bacterium undergoes selection in the CF lung environment over the course of these life-long infections. One genetic adaptation frequently observed in CF P. aeruginosa isolates is mutation of mucA. MucA inhibits the sigma factor AlgU. Clinical mucA mutations lead to misregulation of AlgU, resulting in a mucoid bacterial phenotype that is associated with poor CF disease outcomes. Here we show that paradoxically a portion of the mucA gene is essential for P. aeruginosa viability. We demonstrate that mucA is no longer essential in a strain lacking algU, and mucA alleles that encode for proteins that do not bind to AlgU are insufficient for bacterial viability. Furthermore, we found that mucA is no longer essential in mutant strains containing AlgU variants with reduced sigma factor activity, suggesting that reducing AlgU activity can suppress the requirement for mucA. Finally, we found that overexpression of algU from an inducible promoter prevents cell growth in the absence of MucA, and that this phenotype can be rescued by overproduction of RpoD, the housekeeping sigma factor. Together, these results suggest that in the absence of MucA, the inability to regulate AlgU activity leads to sigma factor competition, preventing the expression of essential housekeeping genes and resulting in the loss of bacterial viability.

The Pseudomonas aeruginosa homeostasis enzyme AlgL clears the periplasmic space of accumulated alginate during polymer biosynthesis

“…Considering the potential significance of a constitutively active AlgU/T in P. aeruginosa (75), we might speculate that studies investigating algL in the mucA22 strain FRD1 may demonstrate similar phenotypes as were reported in our mucA22 ∆algL ∆algD::algD strain and in PDO300 (76). However, in FRD1 with the alginate operon isolated and under the control of an isopropyl β-D-1-thiogalactopyranoside (IPTG)-inducible promoter, a different phenotype was observed (47).…”

Bacterial Alginate Biosynthesis and Metabolism

“…The regulatory proteins encoded by the mucABCD operon are found either embedded in the inner cell membrane or soluble in the periplasmic space. MucA is a transmembrane protein that has anti-δ E activity and acts as a negative regulator of AlgU and is required for maintaining cell viability in P. aeruginosa [94]. MucB has a hydrophobic cavity that interacts with MucA forming a stable complex (MucA-MucB) and serving as a fine-tune controlling mechanism that protects MucA from cleavage of its periplasmic domains by proteases [95,96].…”