A complex multilevel attack on Pseudomonas aeruginosa algT/U expression and algT/U activity results in the loss of alginate production |
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Authors: | Sautter Robert Ramos Damaris Schneper Lisa Ciofu Oana Wassermann Tina Koh Chong-Lek Heydorn Arne Hentzer Morton Høiby Niels Kharazmi Arsalan Molin Søren Devries Caroline A Ohman Dennis E Mathee Kalai |
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Affiliation: | Department of Biological Sciences, College of Arts and Sciences, Florida International University, Miami, FL 33199, USA. |
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Abstract: | Infection by the opportunistic pathogen Pseudomonas aeruginosa is a leading cause of morbidity and mortality seen in cystic fibrosis (CF) patients. This is mainly due to the genotypic and phenotypic changes of the bacteria that cause conversion from a typical nonmucoid to a mucoid form in the CF lung. Mucoid conversion is indicative of overproduction of a capsule-like polysaccharide called alginate. The alginate-overproducing (Alg(+)) mucoid phenotype seen in the CF isolates is extremely unstable. Low oxygen tension growth of mucoid variants readily selects for nonmucoid variants. The switching off mechanism has been mapped to the algT/U locus, and the molecular basis for this conversion was partially attributed to mutations in the algT/U gene itself. To further characterize molecular changes resulting in the unstable phenotype, an isogenic PAO1 derivative that is constitutively Alg(+) due to the replacement of the mucA with mucA22 (PDO300) was used. The mucA22 allele is common in mucoid CF isolates. Thirty-four spontaneous nonmucoid variants, or sap (suppressor of alginate production) mutants, of PDO300 were isolated under low oxygen tension. About 40% of the sap mutants were rescued by a plasmid carrying algT/U (Group A). The remaining sap mutants were not (Group B). The members of Group B fall into two subsets: one similar to PAO1, and another comparable to PDO300. Sequence analysis of the algT/U and mucA genes in Group A shows that mucA22 is intact, whereas algT/U contains mutations. Genetic complementation and sequencing of one Group B sap mutant, sap22, revealed that the nonmucoid phenotype was due to the presence of a mutation in PA3257. PA3257 encodes a putative periplasmic protease. Mutation of PA3257 resulted in decreased algT/U expression. Thus, inhibition of algT/U is a primary mechanism for alginate synthesis suppression. |
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Keywords: | A, adenosine Ala, alanine Alg−, nonmucoid Alg+, alginate overproducing, mucoid ANOLEA, atomic non-local environment assessment Ap, ampicillin Asp, aspartic acid bp, base pair C, cytidine Cb, carbenicillin CF, cystic fibrosis DNA, deoxyribonucleic acid F, phenylalanine G, guanosine Gln, glutamine Gly, glycine Kb, kilobase(s) KDa, kilodalton(s) Km, kanamycin LB, Luria–Bertani broth Leu, leucine Mb, megabase O/N, overnight PAGE, polyacrylamide gel electrophoresis PCR, polymerase chain reaction PIA, Pseudomonas isolation agar Pro, proline Ser, serine SDS, sodium dodecyl sulfate T, thymidine Tc, tetracycline Tn, transposon Trp or W, tryptophan Tyr, tyrosine V, valine |
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