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.
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 (sigma 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 sigma 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::Tcr 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.
Yu
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Department of Microbiology, University of Texas Health Science Center at San Antonio 78284-7758, USA.
Schurr
M J
MJ
Deretic
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V
D000464:Alginates / Q000378:metabolism*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D020723:Glucuronic Acid; D006603:Hexuronic Acids; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D011550:Pseudomonas aeruginosa / Q000235:genetics* / Q000472:pathogenicity; D017382:Reactive Oxygen Species / Q000494:pharmacology; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012808:Sigma Factor / Q000235:genetics*; D014157:Transcription Factors
C079619:AlgU protein, Pseudomonas aeruginosa; D000464:Alginates; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D006603:Hexuronic Acids; D008565:Membrane Proteins; C063757:MucA protein, Bacteria; D017382:Reactive Oxygen Species; C433802:RseA protein, E coli; D012808:Sigma Factor; D014157:Transcription Factors; C063202:sporulation-specific sigma factors; D020723:Glucuronic Acid