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Rapid diversification of Pseudomonas aeruginosa in cystic fibrosis lung-like conditions.

ABSTRACT: Chronic infection of the cystic fibrosis (CF) airway by the opportunistic pathogen Pseudomonas aeruginosa is the leading cause of morbidity and mortality for adult CF patients. Prolonged infections are accompanied by adaptation of P. aeruginosa to the unique conditions of the CF lung environment, as well as marked diversification of the pathogen into phenotypically and genetically distinct strains that can coexist for years within a patient. Little is known, however, about the causes of this diversification and its impact on patient health. Here, we show experimentally that, consistent with ecological theory of diversification, the nutritional conditions of the CF airway can cause rapid and extensive diversification of P. aeruginosa Mucin, the substance responsible for the increased viscosity associated with the thick mucus layer in the CF airway, had little impact on within-population diversification but did promote divergence among populations. Furthermore, in vitro evolution recapitulated traits thought to be hallmarks of chronic infection, including reduced motility and increased biofilm formation, and the range of phenotypes observed in a collection of clinical isolates. Our results suggest that nutritional complexity and reduced dispersal can drive evolutionary diversification of P. aeruginosa independent of other features of the CF lung such as an active immune system or the presence of competing microbial species. We suggest that diversification, by generating extensive phenotypic and genetic variation on which selection can act, may be a key first step in the development of chronic infections.

SUBMITTER: Schick A

PROVIDER: S-EPMC6196507 | biostudies-literature | 2018 Oct

REPOSITORIES: biostudies-literature

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Rapid diversification of Pseudomonas aeruginosa in cystic fibrosis lung-like conditions.

Schick Alana A Kassen Rees R

Proceedings of the National Academy of Sciences of the United States of America 20181001 42

Chronic infection of the cystic fibrosis (CF) airway by the opportunistic pathogen Pseudomonas aeruginosa is the leading cause of morbidity and mortality for adult CF patients. Prolonged infections are accompanied by adaptation of P. aeruginosa to the unique conditions of the CF lung environment, as well as marked diversification of the pathogen into phenotypically and genetically distinct strains that can coexist for years within a patient. Little is known, however, about the caus ...[more]

PMID: 30275334

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Project description:Epidemic strains of Pseudomonas aeruginosa are highly virulent opportunistic pathogens with increased transmissibility and enhanced antimicrobial resistance. Understanding the cellular mechanisms behind this heightened virulence and resistance is critical. Peptidoglycan (PG) is an integral component of P. aeruginosa cells that is essential to its survival and a target for antimicrobials. Here, we examined the global PG composition of two P. aeruginosa epidemic strains, LESB58 and LESlike1, and compared them to the common laboratory strains PAO1 and PA14. We also examined changes in PG composition when the strains were cultured under nutrient conditions that resembled cystic fibrosis lung infections. We identified 448 unique muropeptides and provide the first evidence for stem peptides modified with O-methylation, meso-diaminopimelic acid (mDAP) deamination, and novel substitutions of mDAP residues within P. aeruginosa PG. Our results also present the first evidence for both d,l- and l,d-endopeptidase activity on the PG sacculus of a Gram-negative organism. The PG composition of the epidemic strains varied significantly when grown under conditions resembling cystic fibrosis (CF) lung infections, showing increases in O-methylated stem peptides and decreases in l,d-endopeptidase activity as well as an increased abundance of de-N-acetylated sugars and l,d-transpeptidase activity, which are related to bacterial virulence and antibiotic resistance, respectively. We also identified strain-specific changes where LESlike1 increased the addition of unique amino acids to the terminus of the stem peptide and LESB58 increased amidase activity. Overall, this study demonstrates that P. aeruginosa PG composition is primarily influenced by nutrient conditions that mimic the CF lung; however, inherent strain-to-strain differences also exist. IMPORTANCE Using peptidoglycomics to examine the global composition of the peptidoglycan (PG) allows insights into the enzymatic activity that functions on this important biopolymer. Changes within the PG structure have implications for numerous physiological processes, including virulence and antimicrobial resistance. The identification of highly unique PG modifications illustrates the complexity of this biopolymer in Pseudomonas aeruginosa. Analyzing the PG composition of clinical P. aeruginosa epidemic strains provides insights into the increased virulence and antimicrobial resistance of these difficult-to-eradicate infections.

Project description:Pseudomonas aeruginosa is a Gram-negative, opportunistic bacterium and a major etiological agent in monogenic disease cystic fibrosis (CF). High density colonies of P. aeruginosa are often isolated from hypoxic mucus plugs in respiratory tract of CF patients, indicating high adaptive capacities of the bacterium. Despite the high prevalence and related patient mortality, the protein machinery enabling the bacterium to adapt to this hypoxic environment remains to be fully elucidated. We investigated this by performing both SWATH mass spectrometry and data-dependent SPS-MS3 of TMT labelled peptides to profile the proteomes of two P. aeruginosa CF isolates, PASS2 and PASS3, and a laboratory reference strain, PAO1, grown under hypoxic stress (O2<1%) and aerobic conditions in media that mimics the nutrient components of the CF lung. 3,967 P. aeruginosa proteins were quantitated (FDR <1%) across all three strains, reflecting approximately 71% of predicted ORFs in PAO1 and representing the most comprehensive proteome of clinically relevant P. aeruginosa to date. Comparative analysis revealed 735, 640 and 364 proteins were altered by two-fold or more when comparing low oxygen to aerobic growth in PAO1, PASS2 and PASS3 respectively. Strikingly, under hypoxic stress, all strains showed concurrent increased abundance of proteins required for both aerobic (cbb3-1 and cbb3-2 terminal oxidases) and anaerobic denitrification and arginine fermentation, with the two clinical isolates showing higher relative expression of proteins in these pathways. Additionally, functional annotation revealed that clinical strains portray a unique expression profile of replication, membrane biogenesis and virulence proteins during hypoxia which may endow these bacteria with a survival advantage. These protein profiles illuminate the diversity of P. aeruginosa mechanisms to adapt to low oxygen and shows that CF isolates initiate a robust molecular response to persist under these conditions.

Project description:RationalePseudomonas aeruginosa, the predominant cause of chronic airway infections of patients with cystic fibrosis, exhibits extensive phenotypic diversity among isolates within and between sputum samples, but little is known about the underlying genetic diversity.ObjectivesTo characterize the population genetic structure of transmissible P. aeruginosa Liverpool Epidemic Strain in chronic infections of nine patients with cystic fibrosis, and infer evolutionary processes associated with adaptation to the cystic fibrosis lung.MethodsWe performed whole-genome sequencing of P. aeruginosa isolates and pooled populations and used comparative analyses of genome sequences including phylogenetic reconstructions and resolution of population structure from genome-wide allele frequencies.Measurements and main resultsGenome sequences were obtained for 360 isolates from nine patients. Phylogenetic reconstruction of the ancestry of 40 individually sequenced isolates from one patient sputum sample revealed the coexistence of two genetically diverged, recombining lineages exchanging potentially adaptive mutations. Analysis of population samples for eight additional patients indicated coexisting lineages in six cases. Reconstruction of the ancestry of individually sequenced isolates from all patients indicated smaller genetic distances between than within patients in most cases.ConclusionsOur population-level analysis demonstrates that coexistence of distinct lineages of P. aeruginosa Liverpool Epidemic Strain within individuals is common. In several cases, coexisting lineages may have been present in the infecting inoculum or assembled through multiple transmissions. Divergent lineages can share mutations via homologous recombination, potentially aiding adaptation to the airway during chronic infection. The genetic diversity of this transmissible strain within infections, revealed by high-resolution genomics, has implications for patient segregation and therapeutic strategies.

Dataset Information

Rapid diversification of Pseudomonas aeruginosa in cystic fibrosis lung-like conditions.

Publications

Rapid diversification of <i>Pseudomonas aeruginosa</i> in cystic fibrosis lung-like conditions.

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