SummaryIn addition to transcriptome and proteome studies, metabolome analysis represents a third complementary approach to identify metabolic pathways and adaptation processes. In order to elucidate basic principles of metabolic versatility of Pseudomonas aeruginosa, we investigated the metabolome profiles of two genetically and morphologically divergent strains, the reference strain PAO1 and the mucoid clinical isolate TBCF10839 in exponential growth and stationary phase in six different carbon sources (cadaverine, casamino acids, citrate, glucose, succinate and tryptone). Both strains exhibited strong similarities in mode of growth; the metabolite patterns were mainly defined by the growth condition. Besides this adaptive response, a basic core metabolism shapes the P. aeruginosa metabolome, independent of growth phase, carbon source and genetic background. This core metabolism includes pathways related to the central energy and amino acid metabolism. These consistently utilized metabolic pathways are closely related to glutamate which represents a dominant metabolite in all conditions analysed. In nutrient-depleted media of stationary phase cultures, P. aeruginosa maintains a specific repertoire of metabolic pathways that are related to the carbon source formerly available. This specified adaptation strategy combined with the invariant basic core metabolism may represent a fundamental requirement for the metabolic versatility of this organism.

SummaryPolymorphonuclear neutrophils are the most important mammalian host defence cells against infections with Pseudomonas aeruginosa. Screening of a signature tagged mutagenesis library of the non-piliated P. aeruginosa strain TBCF10839 uncovered that transposon inactivation of its pilY1 gene rendered the bacterium more resistant against killing by neutrophils than the wild type and any other of the more than 3000 tested mutants. Inactivation of pilY1 led to the loss of twitching motility in twitching-proficient wild-type PA14 and PAO1 strains, predisposed to autolysis and impaired the secretion of quinolones and pyocyanin, but on the other hand promoted growth in stationary phase and bacterial survival in murine airway infection models. The PilY1 population consisted of a major full-length and a minor shorter PilY1* isoform. PilY1* was detectable in small extracellular quinolone-positive aggregates, but not in the pilus. P. aeruginosa PilY1 is not an adhesin on the pilus tip, but assists in pilus biogenesis, twitching motility, secretion of secondary metabolites and in the control of cell density in the bacterial population.

Summary Microevolution of closely related Pseudomonas aeruginosa was compared in the clone TB strains TBCF10839 and TBCF121838 which had been isolated from two unrelated individuals with cystic fibrosis who had acquired clone TB during a local outbreak. Compared with the strain PAO1 reference sequence the two clone TB genomes shared 23 155 nucleotide exchanges, 32 out‐of‐frame indels in the coding region and another repertoire of replacement and genomic islands such as PAGI‐1, PAGI‐2, PAGI‐5, LESGI‐1 and LES‐prophage 4. Only TBCF121838 carried a genomic island known from Ralstonia pickettii. Six of the seven strain‐specific sequence variations in the core genome were detected in genes affecting motility, biofilm formation or virulence, i.e. non‐synonymous nucleotide substitutions in mexS, PA3729, PA5017, mifR, a frameshift mutation in pilF (TBCF121838) and an intragenic deletion in pilQ (TBCF10839). Despite their almost identical genome sequence the two strains differed strongly from each other in transcriptome and metabolome profiles, mucin adherence and phagocytosis assays. TBCF121838 was susceptible to killing by neutrophils, but TBCF10839 could grow in leucocytes. Microevolution in P. aeruginosa apparently can generate novel complex traits by few or even single mutations provided that predisposing mutational events had occurred before in the clonal lineage.