Pseudomonas aeruginosa Population Structure Revisited

At present there are strong indications that Pseudomonas aeruginosa exhibits an epidemic population structure; clinical isolates are indistinguishable from environmental isolates, and they do not exhibit a specific (disease) habitat selection. However, some important issues, such as the worldwide emergence of highly transmissible P. aeruginosa clones among cystic fibrosis (CF) patients and the spread and persistence of multidrug resistant (MDR) strains in hospital wards with high antibiotic pressure, remain contentious. To further investigate the population structure of P. aeruginosa, eight parameters were analyzed and combined for 328 unrelated isolates, collected over the last 125 years from 69 localities in 30 countries on five continents, from diverse clinical (human and animal) and environmental habitats. The analysed parameters were: i) O serotype, ii) Fluorescent Amplified-Fragment Length Polymorphism (FALFP) pattern, nucleotide sequences of outer membrane protein genes, iii) oprI, iv) oprL, v) oprD, vi) pyoverdine receptor gene profile (fpvA type and fpvB prevalence), and prevalence of vii) exoenzyme genes exoS and exoU and viii) group I pilin glycosyltransferase gene tfpO. These traits were combined and analysed using biological data analysis software and visualized in the form of a minimum spanning tree (MST). We revealed a network of relationships between all analyzed parameters and non-congruence between experiments. At the same time we observed several conserved clones, characterized by an almost identical data set. These observations confirm the nonclonal epidemic population structure of P. aeruginosa, a superficially clonal structure with frequent recombinations, in which occasionally highly successful epidemic clones arise. One of these clones is the renown and widespread MDR serotype O12 clone. On the other hand, we found no evidence for a widespread CF transmissible clone. All but one of the 43 analysed CF strains belonged to a ubiquitous P. aeruginosa “core lineage” and typically exhibited the exoS+/exoU− genotype and group B oprL and oprD alleles. This is to our knowledge the first report of an MST analysis conducted on a polyphasic data set

Fitness of Isogenic Colony Morphology Variants of Pseudomonas aeruginosa in Murine Airway Infection

Chronic lung infections with Pseudomonas aeruginosa are associated with the diversification of the persisting clone into niche specialists and morphotypes, a phenomenon called ‘dissociative behaviour’. To explore the potential of P. aeruginosa to change its morphotype by single step loss-of–function mutagenesis, a signature-tagged mini-Tn5 plasposon library of the cystic fibrosis airway isolate TBCF10839 was screened for colony morphology variants under nine different conditions in vitro. Transposon insertion into 1% of the genome changed colony morphology into eight discernable morphotypes. Half of the 55 targets encode features of primary or secondary metabolism whereby quinolone production was frequently affected. In the other half the transposon had inserted into genes of the functional categories transport, regulation or motility/chemotaxis. To mimic dissociative behaviour of isogenic strains in lungs, pools of 25 colony morphology variants were tested for competitive fitness in an acute murine airway infection model. Six of the 55 mutants either grew better or worse in vivo than in vitro, respectively. Metabolic proficiency of the colony morphology variant was a key determinant for survival in murine airways. The most common morphotype of self-destructive autolysis did unexpectedly not impair fitness. Transposon insertions into homologous genes of strain PAO1 did not reproduce the TBCF10839 mutant morphotypes for 16 of 19 examined loci pointing to an important role of the genetic background on colony morphology. Depending on the chosen P. aeruginosa strain, functional genome scans will explore other areas of the evolutionary landscape. Based on our discordant findings of mutant phenotypes in P. aeruginosa strains PAO1, PA14 and TBCF10839, we conclude that the current focus on few reference strains may miss modes of niche adaptation and dissociative behaviour that are relevant for the microevolution of complex traits in the wild

Extreme genome diversity in the hyper-prevalent parasitic eukaryote Blastocystis

Blastocystis is the most prevalent eukaryotic microbe colonizing the human gut, infecting approximately 1 billion individuals worldwide. Although Blastocystis has been linked to intestinal disorders, its pathogenicity remains controversial because most carriers are asymptomatic. Here, the genome sequence of Blastocystis subtype (ST) 1 is presented and compared to previously published sequences for ST4 and ST7. Despite a conserved core of genes, there is unexpected diversity between these STs in terms of their genome sizes, guanine-cytosine (GC) content, intron numbers, and gene content. ST1 has 6,544 protein-coding genes, which is several hundred more than reported for ST4 and ST7. The percentage of proteins unique to each ST ranges from 6.2% to 20.5%, greatly exceeding the differences observed within parasite genera. Orthologous proteins also display extreme divergence in amino acid sequence identity between STs (i.e., 59%–61%median identity), on par with observations of the most distantly related species pairs of parasite genera. The STs also display substantial variation in gene family distributions and sizes, especially for protein kinase and protease gene families, which could reflect differences in virulence. It remains to be seen to what extent these inter-ST differences persist at the intra-ST level. A full 26% of genes in ST1 have stop codons that are created on the mRNA level by a novel polyadenylation mechanism found only in Blastocystis. Reconstructions of pathways and organellar systems revealed that ST1 has a relatively complete membrane-trafficking system and a near-complete meiotic toolkit, possibly indicating a sexual cycle. Unlike some intestinal protistan parasites, Blastocystis ST1 has near-complete de novo pyrimidine, purine, and thiamine biosynthesis pathways and is unique amongst studied stramenopiles in being able to metabolize ?-glucans rather than ?-glucans. It lacks all genes encoding heme-containing cytochrome P450 proteins. Predictions of the mitochondrion-related organelle (MRO) proteome reveal an expanded repertoire of functions, including lipid, cofactor, and vitamin biosynthesis, as well as proteins that may be involved in regulating mitochondrial morphology and MRO/endoplasmic reticulum (ER) interactions. In sharp contrast, genes for peroxisome-associated functions are absent, suggesting Blastocystis STs lack this organelle. Overall, this study provides an important window into the biology of Blastocystis, showcasing significant differences between STs that can guide future experimental investigations into differences in their virulence and clarifying the roles of these organisms in gut health and disease

Processing and characterization of wood plastic composites from bio-based polyamide 11 and chemically modified beech fibers

In this study, the reinforcement of bio-based Polyamide 11 (PA 11) with physico-chemically modified Beech Fibers was investigated. In a first step, an improvement of the thermal stability of the fibers was achieved by a two-step alkaline treatment with sodium hydroxide and hydrogen peroxide. This effect was attributed to the removal of the hemicellulose from the fiber surface, as verified by Attenuated Total Reflection Infrared Spectroscopy (ATR-FTIR). Consequently, the onset-temperature of thermal degradation as measured by Thermo-Gravimetric Analysis (TGA) increased from 285 °C to 337 °C. Given this, the compounding of the modified fibers with the low melting bio-based Polyamide 11 was done in a lab-scale co-kneader and followed by subsequent injection molding of test specimens. Analysis of the mechanical and thermo-mechanical properties of the processed Wood Plastic Composites showed a beneficial effect of the chemical fiber treatment on composite stiffness, and allowed for suggestions to improve the up scaling of the processing

Polymerverbund für die Photovoltaik: Ermittlung von Haftfestigkeiten innerhalb eines Polymerverbundes

Erneuerbare Energien gewinnen zunehmend an Bedeutung und werden mit unterschiedlichen Maßnahmen gefördert. Die Nutzung der Solarstrahlung in Photovoltaikanlagen stellt dabei einen Schwerpunkt vieler Forschungs- und Entwicklungsvorhaben dar. Im Bereich der Photovoltaik existieren verschiedene Solarmodulkonzepte. Die gebräuchlichsten Varianten sind gerahmte Module sowie Doppelglasmodule. Als Rahmenwerkstoff werden überwiegend Aluminiumlegierungen verwendet. Der zur Verkapselung der Solarzellen notwendige und energieintensive Laminierprozess sowie die kostenintensive Herstellung der Gläser und Aluminiumrahmen geben Anlass, die Entwicklung alternativer Modulkonzepte voranzutreiben

Mechanical and thermo-mechanical properties of discontinuously and continuously processed biogenic wood-plastic composites from polyamide 11 and chemically modified beech particles

The resulting mechanical and thermo-mechanical properties of discontinuously and continuously processed biogenic wood-plastic composites (bio-WPC) from polyamide 11 and chemically modified beech particles are investigated. It is found that continuous processing with a twin-screw extruder (TSE) and subsequent industrial scale injection molding leads to a lower elastic modulus, an equal tensile strength, a higher strain at break and a lower glass transition temperature as compared to discontinuous processing with an internal mixer (IM) and subsequent laboratory scale injection molding. This is attributed to a more distinctive beech particle size reduction and shear stress induced chain scission during TSE processing and subsequent injection molding