The Susceptibility of Pseudomonas aeruginosa Strains from Cystic Fibrosis Patients to Bacteriophages

Phage therapy may become a complement to antibiotics in the treatment of chronic Pseudomonas aeruginosa infection. To design efficient therapeutic cocktails, the genetic diversity of the species and the spectrum of susceptibility to bacteriophages must be investigated. Bacterial strains showing high levels of phage resistance need to be identified in order to decipher the underlying mechanisms. Here we have selected genetically diverse P. aeruginosa strains from cystic fibrosis patients and tested their susceptibility to a large collection of phages. Based on plaque morphology and restriction profiles, six different phages were purified from “pyophage”, a commercial cocktail directed against five different bacterial species, including P. aeruginosa. Characterization of these phages by electron microscopy and sequencing of genome fragments showed that they belong to 4 different genera. Among 47 P. aeruginosa strains, 13 were not lysed by any of the isolated phages individually or by pyophage. We isolated two new phages that could lyse some of these strains, and their genomes were sequenced. The presence/absence of a CRISPR-Cas system (Clustered Regularly Interspaced Short Palindromic Repeats and Crisper associated genes) was investigated to evaluate the role of the system in phage resistance. Altogether, the results show that some P. aeruginosa strains cannot support the growth of any of the tested phages belonging to 5 different genera, and suggest that the CRISPR-Cas system is not a major defence mechanism against these lytic phages.     

Ring-based versus disc-based separation of spatial scales: a case study on the impact of arable land proportions on invertebrates in freshwater streams

The impact of different land-use types on species is traditionally estimated by correlating landscape proportions recorded in buffer areas around focal points with species data observed at these sites. If a high proportion of a specific land-use type exists within a small radius, it will be accumulated in larger buffers and may confound the interpretation at larger scales. We sampled freshwater invertebrates in ten streams using cages with artificial substrate and compared the effects of arable land proportions calculated in disc-shaped buffers of increasing radius versus areas calculated from non-overlapping rings of increasing radius. We hypothesize that (1) the accumulative disc-based approach leads to confounding effects across increasing buffer size and that (2) the use of ring-based methods facilitates the identification of relevant scales for conservation measures. The abundance of crustaceans showed a positive relationship with arable land proportions, but Plecoptera abundance and the taxonomic richness of Ephemeroptera and Plecoptera decreased with increasing arable land proportions in the surrounding landscape. Our results further support the presence of confounding effects in disc-based analyses, as correlations between arable land proportions and Crustacea, or Plecoptera, respectively, were affected by the accumulation of small-scale area proportions. The distance at which arable land proportions significantly affected benthic fauna in freshwater streams was consistently shorter if calculated from rings rather than from discs. Although an a priori definition of ring width introduces new challenges, a combined use of disc- and ring-based techniques for the estimation of land-use effects may substantially improve the realization of conservation and protection measures in terrestrial and aquatic systems.     

PKD controls mitotic Golgi complex fragmentation through a Raf–MEK1 pathway

Before entering mitosis, the stacks of the Golgi cisternae are separated from each other, and inhibiting this process delays entry of mammalian cells into mitosis. Protein kinase D (PKD) is known to be involved in Golgi-to–cell surface transport by controlling the biogenesis of specific transport carriers. Here we show that depletion of PKD1 and PKD2 proteins from HeLa cells by small interfering RNA leads to the accumulation of cells in the G2 phase of the cell cycle and prevents cells from entering mitosis. We further provide evidence that inhibition of PKD blocks mitotic Raf-1 and mitogen-activated protein kinase kinase (MEK) activation, and, as a consequence, mitotic Golgi fragmentation, which could be rescued by expression of active MEK1. Finally, Golgi fluorescence recovery after photobleaching analyses demonstrate that PKD is crucial for the cleavage of the noncompact zones of Golgi membranes in G2 phase. Our findings suggest that PKD controls interstack Golgi connections in a Raf-1/MEK1–dependent manner, a process required for entry of the cells into mitosis.     

Increased heart rate variability in mice overexpressing the Cu/Zn superoxide dismutase

Cu/Zn superoxide dismutase (SOD1) is implicated in various pathological conditions including Down's syndrome, neurodegenerative diseases, and afflictions of the autonomic nervous system (ANS). To assess the SOD1 contribution to ANS dysfunction, especially its influence on cardiac regulation, we studied the heart rate variability (HRV) and cardiac arrhythmias in conscious 12-month-old male and female transgenic mice for the human SOD1 gene (TghSOD1). TghSOD1 mice presented heart rate reduction as compared with control FVB/N individuals. All HRV parameters reflecting parasympathetic activity were increased in TghSOD1. Pharmacological studies confirmed that the parasympathetic tone was exacerbated and the sympathetic pathway was functional in TghSOD1 mice. A high frequency of atrioventricular block and premature ventricular contractions was observed in TghSOD1. By biochemical assays we found that SOD1 activities were multiplied by 9 and 4 respectively in the heart and brainstem of transgenic mice. A twofold decrease in cholinesterase activity was observed in the heart but not in the brainstem. We demonstrate that SOD1 overexpression induces an ANS dysfunction by an exacerbated vagal tone that may be related to impaired cardiac activity of the cholinesterases and may explain the high occurrence of arrhythmias.     

Plant-insect communities and predator-prey ratios in field margin strips,adjacent crop fields,and fallows

The management of field margin strips for the enhancement of biodiversity of plant-insect communities and natural-enemy populations was studied on experimental farms near Göttingen (Germany). Young and old, sown and naturally developed field margin strips were compared and differences to large fallows established. The five types of field margin strips (around cereal fields) were: (1, 2) 1- or 6-year-old naturally developed strips, (3) strips sown with a Phacelia mixture, (4) strips sown with a mixture of 19 wild flower species, and (5) strips sown with winter wheat or oat as a control. The naturally developed vegetation of the field margin strips was dominated by aggressive weeds, presumably due to the intensive farming practices and the fertile soils. Cirsium arvense populations decreased, while Elymus repens populations increased with age of habitat. Sowings were suitable to suppress these aggressive weeds. Potted plants of mugwort (Artemisia vulgaris) and red clover (Trifolium pratense) were exposed in the field margin strips to study arthropod colonization of these experimentally standardized plant patches. Arthropod species richness did not differ between field margin types, reflecting the overall similarity in floristic diversity, but sprayed and strip-free edges of cereal fields had a reduced diversity. Dispersal of insect populations of red clover into the cereal fields decreased with increasing distance, but benefited from adjacent field margin strips. Populations of predators (mainly spiders) as well as predator-prey ratios were significantly larger in 6-year-old than in 1-year-old strips emphasizing the importance of habitat age for natural enemies and possible biological control. Predator-prey ratios were also higher on old than young fallows. Large fallows had greater predator-prey ratios than small field margin strips emphasizing the trophic-level hypothesis of island biogeography in that the relative importance of natural enemies increased with habitat area. Insect species richness was only marginally influenced by area and not by age. As species richness of predators did not increase with area and age, species diversity and the possible biological-control function did not covary.     

Vertical migration patterns in phytoplankton of mixed species composition

The vertical distribution and migration of phytoplankton composed of seven organisms in a small eutrophic pool is described. Vertical migration during a 24 h period is shown to be exhibited by Pandorina morum, Mallomonas tonsurata, Chroomonas pusilla (Rhodomonas) and Ochromonas sp. in the epilimnion and Cryptomonas rufescens in the surface of the hypolimnion. The degree of horizontal variation in distribution of the organisms is discussed and found to be greatest for the microflagellates. Changes in vertical distribution are shown to be significant and result from active movement of the cells rather than from either water movement or the combined variation associated with patchiness in distribution and counting errors.

Differences between the behaviour patterns of the different algae are evident and may be used to explain Hutchinson's “paradox of the plankton”.