Sequence diversity of the mucABD locus in Pseudomonas aeruginosa isolates from patients with cystic fibrosis

Abstract

The mucA gene of the muc operon, which is instrumental in the control of the biosynthesis of the exopolysaccharide alginate, is a hotspot of mutation in Pseudomonas aeruginosa, a micro-organism that chronically colonizes the airways of individuals with cystic fibrosis (CF). The mucA, mucB and mucD genes were sequenced in nine environmental isolates from aquatic habitats, and in 37 P. aeruginosa strains isolated from 10 patients with CF, at onset or at a late stage of chronic airway colonization, in order to elucidate whether there was any association between mutation and background genotype. The 61 identified single nucleotide polymorphisms (SNPs) segregated into 18 mucABD genotypes. Acquired and de novo stop mucA mutations were present in 14 isolates (38 %) of five mucABD genotypes. ΔG430 was the most frequent and recurrent mucA mutation detected in four genotypes. The classification of strains by mucABD genotype was generally concordant with that by genome-wide SpeI fragment pattern or multilocus SNP genotypes. The exceptions point to intragenic mosaicism and interclonal recombination as major forces for intraclonal evolution at the mucABD locus.

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

“…In agreement with previous studies (Boucher et al, 1997b;Yoon et al, 2006;Bragonzi et al, 2006), mutations in mucA were found to be the main mechanism of conversion to mucoidy. However, we were also able to identify loss-offunction mutations in mucB or mucD in some non-mucoid isolates with increased alginate production on PIA plates (type II) or after prolonged incubation (type IV).…”

“…However, the same types of mutations were also found in unrelated clones from different geographical locations in Scandinavia, suggesting that these loci represent hot-spot regions for mutation in mucA. In addition, the mucA22 mutation was reported previously in several mucoid isolates from the USA, Europe and Australia (Boucher et al, 1997b;Bragonzi et al, 2006;Anthony et al, 2002). Isolates belonging to the Dk1, Dk2 and N clones showed several other types of mutations.…”

“…Interestingly, the more common single-point mutations C338T and A631G found in mucB or A409G, C673G and G1321A in mucD that led to amino acid changes in the respective encoded proteins were reported previously in German isolates (Bragonzi et al, 2006) and might suggest that these are hot-spot regions for mutations in mucB and mucD.…”

“…In a recent study of 37 sequential isolates from 10 CF patients attending the Hannover CF Clinic, Germany, mucA mutations were found in both mucoid and nonmucoid isolates but the occurrence of secondary-site mutations responsible for the reversion to the non-mucoid phenotype was not investigated (Bragonzi et al, 2006).…”

The effect of mucA allele on biofilm architecture and the biofilm-related proteomes

“…More than 80% of the frameshift or nonsense mutations that give rise to a premature stop signal are clustered within the 100 bp stretch from nt 340-439 of the 585 bp of the mucA gene. The most common mucA22 allele is characterized by a single base pair deletion at position 430, and it accounts for 40% of all stop mutations (Bragonzi et al, 2006). We isolated a mucoid strain from a patient who suffered from repeated pulmonary infection, which contained a previously unreported mucA allele (designated mucA56) characterized by a deletion of bases 166 to 333, and its sequence in Genebank is AY608668.…”