Functional equivalence of Escherichia coli sigma E and Pseudomonas aeruginosa AlgU: E. coli rpoE restores mucoidy and reduces sensitivity to reactive oxygen intermediates in algU mutants of P. aeruginosa

Abstract

Mucoid colony morphology is the result of the overproduction of the exopolysaccharide alginate and is considered to be a major pathogenic determinant expressed by Pseudomonas aeruginosa during chronic respiratory infections in cystic fibrosis. Conversion to mucoidy can be caused by mutations in the second or third gene of the stress-responsive system algU mucA mucB. AlgU is 66% identical to the alternative sigma factor RpoE ( E ) from Escherichia coli and Salmonella typhimurium and directs transcription of several critical alginate biosynthetic and regulatory genes. AlgU is also required for the full resistance of P. aeruginosa to reactive oxygen intermediates and heat killing. In this work, we report that E. coli E can complement phenotypic defects of algU inactivation in P. aeruginosa: (i) the rpoE gene from E. coli complemented an algU null mutant of P. aeruginosa to mucoidy; (ii) the presence of the E. coli rpoE gene in P. aeruginosa induced alginate production in the standard genetic nonmucoid strain PAO1; (iii) the plasmid-borne E. coli rpoE gene induced transcription of algD, a critical algU-dependent alginate biosynthetic gene; and (iv) when present in algU::Tc r mutants, E. coli rpoE partially restored resistance to paraquat, a redox cycling compound that increases intracellular levels of superoxide radicals. A new gene, mclA, encoding a polypeptide with an apparent molecular mass of 27.7 kDa was identified immediately downstream of rpoE in E. coli. The predicted product of this gene is 28% identical (72% similar) to MucA, a negative regulator of AlgU activity in P. aeruginosa. The results reported in this study demonstrate that RpoE and AlgU are functionally interchangeable in P. aeruginosa and suggest that elements showing sequence similarity to those known to regulate AlgU activity in P. aeruginosa are also present in other bacteria.

Truncated type IV pilin PilA108 activates the intramembrane protease AlgW to cleave MucA and PilA108 itself in vitro

“…AlgU is 66 % identical to the ECF σ factor RpoE (Yu et al 1995) which is regulated via the regulated intramembrane proteolysis of the cognate anti-σ factor RseA in response to envelope stress signals in E. coli (Alba et al 2001(Alba et al , 2002Helmann 2002;Kanehara et al 2003;Walsh et al 2003). This mechanism of regulation is consistent in P. aeruginosa (Qiu et al 2007(Qiu et al , 2008Cezairliyan and Sauer 2009;Wood and Ohman 2009).…”

Microbial pathogenesis in cystic fibrosis: co‐ordinate regulation of heat‐shock response and conversion to mucoidy in Pseudomonas aeruginosa

“…The initial experimental evidence supporting the hypothesis that algU encodes the P. aeruginosa equivalent of E was presented when E. coli rpoE was shown to complement an algU mutation and to induce mucoidy in P. aeruginosa (Yu et al, 1995). Biochemical evidence that algU encodes a sigma factor has been reported recently (Hershberger et al, 1995;Schurr et al, 1995b).…”

“…Because of this cascade of regulatory interactions, the net result of a loss of mucA is alginate overproduction and mucoid colony phenotype. The equivalence of E. coli E and P. aeruginosa AlgU suggests that there may be broader physiological overlaps in the function of these sigma factors (Yu et al, 1995). The sigma factor 32 that controls the heat-shock response in E. coli is encoded by the rpoH gene (Grossman et al, 1984).…”

Investigation of the algT operon sequence in mucoid and non-mucoid Pseudomonas aeruginosa isolates from 115 Scandinavian patients with cystic fibrosis and in 88 in vitro non-mucoid revertants

“…Congruent with the functions played by the s E in E. coli, AlgT is involved in the regulation of a number of other systems in P. aeruginosa, such as heat shock, osmotic protection and protection against reactive oxygen species Yu et al, 1995;Firoved et al, 2002). It has also been shown that AlgT represses flagellum biosynthesis in P. aeruginosa (Tart et al, 2006).…”

“…Besides controlling alginate production, AlgT is the P. aeruginosa equivalent of the extreme heat-shock sigma factor s E of E. coli (Yu et al, 1995). Congruent with the functions played by the s E in E. coli, AlgT is involved in the regulation of a number of other systems in P. aeruginosa, such as heat shock, osmotic protection and protection against reactive oxygen species Yu et al, 1995;Firoved et al, 2002).…”